Special thanks to Dr. Benedikt Steuten for critical reading of the manuscript. The original work on the chitinases was carried out by Dr. Thorsten Langner. The laboratory of VG is supported by the Cluster of Excellence in Plant Sciences (CEPLAS, DFG EXC 1028) and BioSC, the laboratory of KS is supported by BioSC. KB is supported by BioSC. The scientific activities of the Bioeconomy Science Center (BioSC) were financially supported by the Ministry of Innovation, Science and Research within the framework of the NRW Strategieprojekt BioSC (No. 313/323-400-00213). LF is supported by a doctoral fellowship of the DFG International Research Training Group 1525 iGRADplant.

1. Generation of Deletion Constructs
<ol>
	<li>Generate a plasmid containing the deletion construct (Figure 1) comprising a respective 1 kb upstream flank (UF) and downstream flank (DF) each and the appropriate resistance cassette flanked by blunt cutting restriction sites. 
	NOTE: Any cloning strategy can be used (for cloning see reference 22) we recommend Golden Gate cloning for such plasmids 9.</li>
	<li>Excise the deletion construct from the plasmid using a blunt cutter t...

<ol>
	<li>Dean, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Top+10+fungal+pathogens+in+molecular+plant+pathology.">The Top 10 fungal pathogens in molecular plant pathology.</a> Molecular Plant Pathology. 13, 414-430 (2012).</li><li>Vollmeister, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fungal+development+of+the+plant+pathogen+Ustilago+maydis.">Fungal development of the plant pathogen Ustilago maydis.</a> Fems Microbiol Rev. 36, 59-77 (2012).</li><li>Banuett, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ustilago+maydis,+the+delightful+blight.">Ustilago maydis, the delightful blight.</a> Trends in Genetics. 8, 174-180 (1992).</li><li>Holloman, W. K., Schirawski, J., Holliday, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+homologous+recombination+system+of+Ustilago+maydis.">The homologous recombination system of Ustilago maydis.</a> Fungal Genetics and Biology. 45, S31-S39 (2008).</li><li>Feldbr&#252;gge, M., K&#228;mper, J., Steinberg, G., Kahmann, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+mating+and+pathogenic+development+in+Ustilago+maydis.">Regulation of mating and pathogenic development in Ustilago maydis.</a> Current Opinion in Microbiology. 7, 666-672 (2004).</li><li>&#214;kmen, B., Doehlemann, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inside+plant:+Biotrophic+strategies+to+modulate+host+immunity+and+metabolism.">Inside plant: Biotrophic strategies to modulate host immunity and metabolism.</a> Current Opinion in Plant Biology. 20, 19-25 (2014).</li><li>Brachmann, A., K&#246;nig, J., Julius, C., Feldbr&#252;gge, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+reverse+genetic+approach+for+generating+gene+replacement+mutants+in+Ustilago+maydis.">A reverse genetic approach for generating gene replacement mutants in Ustilago maydis.</a> Molecular Genetics and Genomics. 272, 216-226 (2004).</li><li>K&#228;mper, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+PCR-based+system+for+highly+efficient+generation+of+gene+replacement+mutants+in+Ustilago+maydis.">A PCR-based system for highly efficient generation of gene replacement mutants in Ustilago maydis.</a> Molecular Genetics and Genomics. 271, 103-110 (2004).</li><li>Terfr&#252;chte, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Establishing+a+versatile+Golden+Gate+cloning+system+for+genetic+engineering+in+fungi.">Establishing a versatile Golden Gate cloning system for genetic engineering in fungi.</a> Fungal Genetics and Biology. 62, 1-10 (2014).</li><li>K&#228;mper, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insights+from+the+genome+of+the+biotrophic+fungal+plant+pathogen+Ustilago+maydis.">Insights from the genome of the biotrophic fungal plant pathogen Ustilago maydis.</a> Nature. 444, 97-101 (2006).</li><li>Chavan, S., Smith, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Rapid+and+Efficient+Method+for+Assessing+Pathogenicity+of+Ustilago+maydis+on+Maize+and+Teosinte+Lines.">A Rapid and Efficient Method for Assessing Pathogenicity of Ustilago maydis on Maize and Teosinte Lines.</a> Journal of Visualized Experiments. (83), e50712 (2014).</li><li>Khrunyk, Y., M&#252;nch, K., Schipper, K., Lupas, A. N., Kahmann, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+FLP-mediated+recombination+for+the+functional+analysis+of+an+effector+gene+family+in+the+biotrophic+smut+fungus+Ustilago+maydis.">The use of FLP-mediated recombination for the functional analysis of an effector gene family in the biotrophic smut fungus Ustilago maydis.</a> New Phytologist. 187, 957-968 (2010).</li><li>van Peer, A. F., de Bekker, C., Vinck, A., W&#246;sten, H. A. B., Lugones, L. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phleomycin+Increases+Transformation+Efficiency+and+Promotes+Single+Integrations+in+Schizophyllum+commune.">Phleomycin Increases Transformation Efficiency and Promotes Single Integrations in Schizophyllum commune.</a> Appl Environ Microb. 75, 1243-1247 (2009).</li><li>Sarkari, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+expression+of+single-chain+antibodies+in+Ustilago+maydis.">Improved expression of single-chain antibodies in Ustilago maydis.</a> Journal of Biotechnology. 191, 165-175 (2014).</li><li>Schirawski, J., Heinze, B., Wagenknecht, M., Kahmann, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mating+type+loci+of+Sporisorium+reilianum:+Novel+pattern+with+three+a+and+multiple+b+specificities.">Mating type loci of Sporisorium reilianum: Novel pattern with three a and multiple b specificities.</a> Eukaryotic Cell. 4, 1317-1327 (2005).</li><li>Cervantes-Chavez, J. A., Ali, S., Bakkeren, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Response+to+Environmental+Stresses,+Cell-wall+Integrity,+and+Virulence+Are+Orchestrated+Through+the+Calcineurin+Pathway+in+Ustilago+hordei.">Response to Environmental Stresses, Cell-wall Integrity, and Virulence Are Orchestrated Through the Calcineurin Pathway in Ustilago hordei.</a> Mol Plant Microbe In. 24, 219-232 (2011).</li><li>Yu, J. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+efficient+genetic+manipulation+protocol+for+Ustilago+esculenta.">An efficient genetic manipulation protocol for Ustilago esculenta.</a> FEMS Microbiology Letters. 362, (2015).</li><li>Ninomiya, Y., Suzuki, K., Ishii, C., Inoue, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+efficient+gene+replacements+in+Neurospora+strains+deficient+for+nonhomologous+end-joining.">Highly efficient gene replacements in Neurospora strains deficient for nonhomologous end-joining.</a> P Natl Acad Sci USA. 101, 12248-12253 (2004).</li><li>Colot, H. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+high-throughput+gene+knockout+procedure+for+Neurospora+reveals+functions+for+multiple+transcription+factors.">A high-throughput gene knockout procedure for Neurospora reveals functions for multiple transcription factors.</a> P Natl Acad Sci USA. 103, 10352-10357 (2006).</li><li>Langner, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chitinases+Are+Essential+for+Cell+Separation+in+Ustilago+maydis.">Chitinases Are Essential for Cell Separation in Ustilago maydis.</a> Eukaryot Cell. 14, 846-857 (2015).</li><li>Langner, T., G&#246;hre, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fungal+chitinases:+function,+regulation,+and+potential+roles+in+plant/pathogen+interactions.">Fungal chitinases: function, regulation, and potential roles in plant/pathogen interactions.</a> Current Genetics. , (2015).</li><li>Sambrook, J., Fritsch, E. F., Maniatis, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Molecular Cloining: a laboratry manual. , (1989).</li><li>Brachmann, A., Weinzierl, G., K&#228;mper, J., Kahmann, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+genes+in+the+bW/bE+regulatory+cascade+in+Ustilago+maydis.">Identification of genes in the bW/bE regulatory cascade in Ustilago maydis.</a> Molecular Microbiology. 42, 1047-1063 (2001).</li><li>Becht, P., Vollmeister, E., Feldbr&#252;gge, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+for+RNA-binding+proteins+implicated+in+pathogenic+development+of+Ustilago+maydis.">Role for RNA-binding proteins implicated in pathogenic development of Ustilago maydis.</a> Eukaryotic Cell. 4, 121-133 (2005).</li><li>Vollmeister, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tandem+KH+domains+of+Khd4+recognize+AUACCC+and+are+essential+for+regulation+of+morphology+as+well+as+pathogenicity+in+Ustilago+maydis.">Tandem KH domains of Khd4 recognize AUACCC and are essential for regulation of morphology as well as pathogenicity in Ustilago maydis.</a> RNA. 15, 2206-2218 (2009).</li><li>Stock, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Applying+unconventional+secretion+of+the+endochitinase+Cts1+to+export+heterologous+proteins+in+Ustilago+maydis.">Applying unconventional secretion of the endochitinase Cts1 to export heterologous proteins in Ustilago maydis.</a> Journal of Biotechnology. 161, 80-91 (2012).</li><li>Baumann, S., Pohlmann, T., Jungbluth, M., Brachmann, A., Feldbr&#252;gge, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinesin-3+and+dynein+mediate+microtubule-dependent+co-transport+of+mRNPs+and+endosomes.">Kinesin-3 and dynein mediate microtubule-dependent co-transport of mRNPs and endosomes.</a> Journal of Cell Science. 125, 2740-2752 (2012).</li><li>Pohlmann, T., Baumann, S., Haag, C., Albrecht, M., Feldbr&#252;gge, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+FYVE+zinc+finger+domain+protein+specifically+links+mRNA+transport+to+endosome+trafficking.">A FYVE zinc finger domain protein specifically links mRNA transport to endosome trafficking.</a> eLife. 4, (2015).</li><li>Kronstad, J. 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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+two+Alleles+of+the+b-Locus+of+Ustilago.">Isolation of two Alleles of the b-Locus of Ustilago.</a> P Natl Acad Sci USA. 86, 978-982 (1989).</li><li>Koepke, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+RNA-binding+protein+Rrm4+is+essential+for+efficient+secretion+of+endochitinase+Cts1.">The RNA-binding protein Rrm4 is essential for efficient secretion of endochitinase Cts1.</a> Molecular &amp; cellular proteomics. 10, (2011).</li><li>Schuler, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hxt1,+a+monosaccharide+transporter+and+sensor+required+for+virulence+of+the+maize+pathogen+Ustilago+maydis.">Hxt1, a monosaccharide transporter and sensor required for virulence of the maize pathogen Ustilago maydis.</a> New Phytologist 206. , 1086-1100 (2015).</li><li>Schuster, M., Schweizer, G., Reissmann, S., Kahmann, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genome+editing+in+Ustilago+maydis+using+the+CRISPR-Cas+system.">Genome editing in Ustilago maydis using the CRISPR-Cas system.</a> Fungal Genetics and Biology. , (2015).</li></ol>

This protocol describes how to generate deletion mutants for reverse genetic studies in U. maydis. The starting point is a deletion construct that contains flanking sequences of the gene-of-interest containing sequences of about 1 kb upstream of the start and downstream of the stop-codon as well as an appropriate resistance cassette as it was previously optimized 7,9. The constructs have to be individually generated for each gene and carefully verified for sequence errors prior to deleting the gene. P...

Ustilago maydis is a phytopathogenic model fungus that has been studied extensively for decades 1,2. It exists in two morphologies, a yeast-like, non-pathogenic stage and a filamentous, infectious form 3. Universal breakthrough discoveries such as homologous recombination and DNA repair mechanisms were made in the yeast-like growth stage of this fungus 4. Furthermore, the morphological switch to the infectious filament and virulence factors important for infection are well-characterized 5,6. The increasing molecular knowledge about biology and virulence of this smut fungus relies on a straightforward gene replacement strategy 7-9 supported by an excellent genome annotation 10 and the ease of reverse genetics using, e.g., the well-organized plasmid collection at our institute (http://www.mikrobiologie.hhu.de/ustilago-community.html). Standardized, rapid infection assays in maize seedlings allow detailed studies of pathogenicity factors 11.
The genome of U. maydis contains about 6,900 genes 10. To study their function, they can be deleted individually or in combination due to an efficient homologous recombination system. Flanking regions of about 1 kb containing perfectly homologous ends are ideal for rates of homologous recombination greater than 50%, but already 250 bp with non-homologous ends allow some degree of correct integration of the construct 9. Currently, five different resistance cassettes, hygR, cbxR, natR, G418R, and phleoR mediating resistance against hygromycin, carboxin, nourseothricin, G418 and phleomycin, are employed to select for transformants 7,9. In addition, the hygromycin resistance has been developed into a recyclable cassette (FRT-hygR) that can be removed by the transient expression of a heterologous&#160;FLP recombinase 12. This allows removal of the resistance cassette and thereby in theory unlimited genetic modifications. Phleomycin is mutagenic 13, so that with the new cassettes, in particular the recyclable hygR cassette, the use of phleoR is decreasing. Quadruple mutants can thus be generated using the other four cassettes, but for quintuple mutants, the FRT-hygR system is recommended 14.
This general gene deletion strategy has been successfully transferred to other smut fungi such as Sporisorium reilianum 15, U. hordei 16, or U. esculenta 17 and therefore offers the potential for further applications in yet genetically intractable organisms with an efficient homologous recombination system. Moreover, organisms lacking homologous recombination can be modified to improve genetic engineering as exemplified by the deletion of genes involved in non-homologous-end-joining in Neurospora crassa 18,19.
Here we describe the published gene deletion strategy for U. maydis 7,9 in experimental detail with a focus on the rapid and accurate verification of the candidates. As an example, we use the fungal chitinases and depict the generation of single mutants as well as multiple deletion strains 20,21. Chitinases are interesting examples, because they act on chitin in the rigid cell wall. Cell wall remodeling is required for morphological changes during cell division, switch to filamentous growth, and spore formation. Hence, in deletion mutants phenotypes throughout the lifecycle can be expected.

<table border="0" cellpadding="0" cellspacing="0" width="1138">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Aminobenzoeic acid (Free Acid)</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">A-9878</td>
			<td style="width:485px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bacto Agar&#160;</td>
			<td style="width:183px;">BD</td>
			<td style="width:124px;">214010</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bacto Peptone</td>
			<td style="width:183px;">BD</td>
			<td style="width:124px;">211677</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bacto Yeast Extract&#160;</td>
			<td style="width:183px;">BD</td>
			<td style="width:124px;">212750</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">CaCl2*2H2O</td>
			<td style="width:183px;">Gr&#252;ssing GmbH</td>
			<td style="width:124px;">10234</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Ca-pantothenat (Hemi-Ca. salt)</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">P-2250</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Carboxin&#160;</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">45371</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Casamino acids&#160;</td>
			<td style="width:183px;">BD</td>
			<td style="width:124px;">223050</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Cholinchlorid</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td>C-1879</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Citric acid</td>
			<td style="width:183px;">ChemSolute</td>
			<td style="width:124px;">24,321,000</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">CuSO4*5H2O</td>
			<td style="width:183px;">Fluka</td>
			<td style="width:124px;">61240</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">D(+)Sucrose&#160;</td>
			<td style="width:183px;">Roth</td>
			<td style="width:124px;">4621.1</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">DNA degr. free acid&#160;</td>
			<td style="width:183px;">Sigma-Aldrich</td>
			<td style="width:124px;">D-3159</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">EDTA</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">E4378</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">FeCl3*6H2O</td>
			<td style="width:183px;">Gr&#252;ssing GmbH</td>
			<td style="width:124px;">10288</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Geneticin (G418) disulfate salt</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">A1720</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Trichoderma lysing enzymes</td>
			<td>Sigma Aldrich</td>
			<td>L1412</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Glucose</td>
			<td style="width:183px;">Caelo</td>
			<td style="width:124px;">2580</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Glycerin&#160;</td>
			<td style="width:183px;">Fisher Chemical</td>
			<td style="width:124px;">G065015</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">H3BO3</td>
			<td style="width:183px;">AppliChem</td>
			<td style="width:124px;">A2940</td>
			<td>Dangerous substance. Please check manufacturer&#39;s safety instructions.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Heparin sodium salt</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">H3393-50KU</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hygromycin B-solution</td>
			<td style="width:183px;">Roth</td>
			<td style="width:124px;">1287.2</td>
			<td>Dangerous substance.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">KCl</td>
			<td style="width:183px;">VWR</td>
			<td style="width:124px;">26764298</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">KH2PO4</td>
			<td style="width:183px;">AppliChem</td>
			<td style="width:124px;">A3620</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">MgSO4 waterfree</td>
			<td style="width:183px;">Merck</td>
			<td style="width:124px;">7487-88-9</td>
			<td>Water free is critical. Alternatively use local supplier</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">MnCl2*4H2O</td>
			<td style="width:183px;">AppliChem</td>
			<td style="width:124px;">A2087</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">myo-Inositol</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td>I-5125</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">Na2-EDTA*2H2O</td>
			<td style="width:183px;">AppliChem</td>
			<td style="width:124px;">A2937</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">Na2MoO4*2H2O</td>
			<td style="width:183px;">Roth</td>
			<td style="width:124px;">0274.2</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">Na2SO4</td>
			<td style="width:183px;">Gr&#252;ssing GmbH</td>
			<td style="width:124px;">12174</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">NaCl</td>
			<td style="width:183px;">Fisher Chemical</td>
			<td style="width:124px;">S316060</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">NaOH</td>
			<td style="width:183px;">ChemSolute</td>
			<td style="width:124px;">13,751,000</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">NH4NO3</td>
			<td style="width:183px;">Roth</td>
			<td style="width:124px;">K299.1</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Nicotinic acid (Free Acid)</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">N-4126</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Nourseothricin dihydrogen sulfate&#160;&#160;</td>
			<td style="width:183px;">Werner BioAgents</td>
			<td style="width:124px;">5,001,000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Nutrient broth&#160;</td>
			<td style="width:183px;">Difco</td>
			<td style="width:124px;"></td>
			<td>local suppliers</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">Phenol:Chloroform:Isoamyl Alcohol (25:24:1) pH 6.7</td>
			<td>Sigma Aldrich</td>
			<td>P3803</td>
			<td>Dangerous substance. Please check manufacturer&#39;s safety instructions.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">polyethylene glycol (PEG)</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">P-3640</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Potassium acetate</td>
			<td style="width:183px;">AppliChem</td>
			<td>121479</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Pyridoxin (Monohydrochlorid)</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">P-9755</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Riboflavin&#160;</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">R4500</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">RNaseA</td>
			<td style="width:183px;">Sigma Aldrich</td>
			<td style="width:124px;">R5503</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">SDS</td>
			<td style="width:183px;">Roth</td>
			<td style="width:124px;">Cn30.3</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">small syringe</td>
			<td>BD</td>
			<td>300300</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">sterile filter, 22 &#181;m</td>
			<td>VWR</td>
			<td>28145-477</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Sorbitol</td>
			<td style="width:183px;">Roth</td>
			<td style="width:124px;">6213.1</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Thiamin-Hydrochloride</td>
			<td style="width:183px;">Serva</td>
			<td style="width:124px;">36020.02</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">tri-Na-Citrate</td>
			<td style="width:183px;">Fisher Chemical</td>
			<td style="width:124px;">S332060</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Tris- (hydroxymethyl) aminomethane</td>
			<td>VWR</td>
			<td style="width:124px;">103156X</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Tris hydrochloride</td>
			<td>Roth</td>
			<td style="width:124px;">9090.4</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Triton X-100&#160;</td>
			<td style="width:183px;">Serva&#160;</td>
			<td style="width:124px;">37240</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:347px;">ZnCl2</td>
			<td style="width:183px;">Fluka</td>
			<td style="width:124px;">96470</td>
			<td>alternatively use local supplier</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:347px;">Name</td>
			<td style="width:183px;">Company</td>
			<td style="width:124px;">Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Composition of solutions/preparation of material</td>
			<td></td>
			<td></td>
			<td>Composition of solutions</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Carboxin</td>
			<td></td>
			<td></td>
			<td>Stock: 5 mg/ml in methanol, final concentration: 2 &#181;g/ml</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">CM plates</td>
			<td></td>
			<td></td>
			<td>0.25 % (w/v) Casamino acids, 0.1 % (w/v) Yeast Extract, 1.0 % (v/v) Holliday vitamin solution, 6.25 % (v/v); Holliday salt solution, 0.05 % (w/v) DNA degr. free acid, 0.15 % (w/v) NH4NO3, 2.0 % (w/v) Bacto Agar; adjust to pH 7.0 using 5 M NaOH; after autoclaving add 1 % glucose&#160;</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Geneticin (G418)</td>
			<td></td>
			<td></td>
			<td>Stock: 50 mg/ml in H2O, final concentration: 500 &#181;g/ml</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">HCl-washed glass beads (0,35-0,45 mm)</td>
			<td></td>
			<td></td>
			<td>Cover glass beads with concentrated HCl (25 %, 7.8 M) and incubate for 60 min. Sway several times. Decant HCl (keep decanted liquid) and wash glass beads with 3 M HCl (keep decanted liquid). Wash glass beads several times with double distilled H2O until the pH is 7 (the liquid should not be yellow-green anymore). Aliquot the glass beads and dry them at 180 &#176;C. The decanted HCl has to be neutralized before disposal.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Heparin</td>
			<td></td>
			<td></td>
			<td>Stock: 15 mg/ml</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Holliday salt solution</td>
			<td></td>
			<td></td>
			<td>16.0 &#8240; (w/v) KH2PO4, 4.0 &#8240; (w/v) Na2SO4, 8.0 &#8240; (w/v) KCl, 1.32 &#8240; (w/v) CaCl2*2H2O, 8.0 &#8240; (v/v) trace elements, 2.0 &#8240; (w/v) MgSO4; sterile filtrate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Holliday vitamin solution&#160;</td>
			<td></td>
			<td></td>
			<td>0.1&#8240; (w/v) Thiamin, 0.05&#8240; (w/v) Riboflavin, 0.05&#8240; (w/v) Pyridoxin, 0.2&#8240; (w/v) Ca-Pantothenat, (0.05&#8240; (w/v) Aminobenzoeic acid, 0.2&#8240; (w/v) Nicotinic acid, 0.2&#8240; (w/v) Cholinchlorid, 1.0&#8240; (w/v) myo-Inositol; may be stored at -20 &#176;C</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hygromycin</td>
			<td></td>
			<td></td>
			<td>Stock: 50 mg/ml in PBS, final concentration: 200 &#181;g/ml</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Nourseothricin</td>
			<td></td>
			<td></td>
			<td>Stock: 200 mg/ml in H2O, final concentration: 150 &#181;g/ml</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NSY-glycerol-medium</td>
			<td></td>
			<td></td>
			<td>0.8 % (w/v) Nutrient Broth, 0.1 % (w/v) Yeast Extract, 0.5 % (w/v) Sucrose,&#160; 80.0 % (v/v) 87% Glycerin (f.c. 69.6%)&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">RegLight</td>
			<td></td>
			<td></td>
			<td>1.0% (w/v) Yeast Extract&#160; 0.4 % (w/v) Bacto Peptone, 0.4 % (w/v) Sucrose, 18.22 % (w/v) Sorbitol, 1.5 % (w/v) Agar</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">SCS, pH 5.8</td>
			<td></td>
			<td></td>
			<td>Solution 1: 20 mM tri-Na-citrate, 1 M Sorbitol; colution 2: 20 mM Citric acid, 1 M Sorbitol, add solution 2 into solution 1 until pH 5.8 is reached; autoclave</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">STC, pH 8</td>
			<td></td>
			<td></td>
			<td>1 M Sorbitol, 10 mM Tris-HCl pH 7.5, 100 mM CaCl2; filter sterile</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">STC/PEG</td>
			<td></td>
			<td></td>
			<td>40 % (v/v) PEG in STC-buffer&#160;</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">TE buffer, pH 8</td>
			<td></td>
			<td></td>
			<td>1.31 mM Tris-Base, 8.69 mM Tris-HCl, 10 mM Na2-EDTA*2H2O</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">TE/RNase</td>
			<td></td>
			<td></td>
			<td>10 &#181;g/ml RNaseA in TE buffer</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Trace elements</td>
			<td></td>
			<td></td>
			<td>0.06&#8240; (w/v) H3BO3, 0.14&#8240; (w/v) MnCl*4H2O, 0.4 &#8240; (w/v) ZnCl2, 0.4 &#8240; (w/v) Na2MoO4*2H2O, 0.1 &#8240; (w/v) FeCl3*6H2O, 0.04&#8240; (w/v) CuSO4*5H2O</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Trichoderma lysing enzymes solution</td>
			<td></td>
			<td></td>
			<td>12.5 mg/ml SCS; filter sterile; prepare shortly before use</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tris-HCl pH 7.5</td>
			<td></td>
			<td></td>
			<td>806 mM Tris-HCl, 194 mM Tris-Base; check the pH and if necessary adjust with HCl; autoclave</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Usti-lysis buffer 1, pH 8</td>
			<td></td>
			<td></td>
			<td>10 mM Tris-HCl (pH 8.0), 10 mM NaCl, 1 % (w/v) SDS, 2 % (v/v) TritonX-100, 1 mM EDTA. Do not measure pH using pH meter.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Usti-lysis buffer 2</td>
			<td></td>
			<td></td>
			<td>mix Usti lysis buffer 1 with 1 x TE in a 1:1 ratio</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">YEPS-Light medium</td>
			<td></td>
			<td></td>
			<td>1.0% (w/v) Yeast Extract, 0.4% (w/v) Bacto Peptone, 0.4% (w/v) Sucrose, for plates: 1.5% (w/v) Bacto Agar</td>
		</tr>
	</tbody>
</table>

genetic manipulation of the plant pathogen ustilago maydis to study fungal biology and plant microbe interactions

Gene deletion plays an important role in the analysis of gene function. One of the most efficient methods to disrupt genes in a targeted manner is the replacement of the entire gene with a selectable marker via homologous recombination. During homologous recombination, exchange of DNA takes place between sequences with high similarity. Therefore, linear genomic sequences flanking a target gene can be used to specifically direct a selectable marker to the desired integration site. Blunt ends of the deletion construct activate the cell&#39;s DNA repair systems and thereby promote integration of the construct either via homologous recombination or by non-homologous-end-joining. In organisms with efficient homologous recombination, the rate of successful gene deletion can reach more than 50% making this strategy a valuable gene disruption system. The smut fungus Ustilago maydis is a eukaryotic model microorganism showing such efficient homologous recombination. Out of its about 6,900 genes, many have been functionally characterized with the help of deletion mutants, and repeated failure of gene replacement attempts points at essential function of the gene. Subsequent characterization of the gene function by tagging with fluorescent markers or mutations of predicted domains also relies on DNA exchange via homologous recombination. Here, we present the U. maydis strain generation strategy in detail using the simplest example, the gene deletion.

The deletion constructs for all four chitinolytic genes encoded in the U. maydis genome were generated by Golden Gate cloning using the hygR cassette for deletion of cts1, the natR for deletion of cts2, the G418R cassette for deletion of cts3 and the cbxR for deletion of cts4 20. A general overview of the gene replacement strategy is exemplified by the deletion of cts3 (Figure 1</s...

Watch this Scientific Journal Video about Genetic Manipulation of the Plant Pathogen Ustilago maydis to Study Fungal Biology and Plant Microbe Interactions at JoVE.com

Genetic Manipulation of the Plant Pathogen Ustilago maydis to Study Fungal Biology and Plant Microbe Interactions

We describe a robust gene replacement strategy to genetically manipulate the smut fungus Ustilago maydis. This protocol explains how to generate deletion mutants to investigate infection phenotypes. It can be extended to modify genes in any desired way, e.g., by adding a sequence encoding a fluorescent protein tag.

Genetic Manipulation of the Plant Pathogen Ustilago maydis to Study Fungal Biology and Plant Microbe Interactions

Gene deletion plays an important role in the analysis of gene function. One of the most efficient methods to disrupt genes in a targeted manner is the ...

The overall goal of this protocol is to genetically modify the smut fungus, ustilago maydis. This strain generation method allows functional characterization of genes in a variety of ways. For example, we can delete the genes, we can exchange the promotus, or we can generate fusion constructs.The main advantage of this method is that we can precisely verify the modification, so that any phenotype can be directly linked to the change in the gene of interest. Visual demonstration of this method is essential, because knowing when to stop the protoplasting reaction is critical for successful transformation. In preparation, cool down two milliliter round bottom tubes at minus 20 degrees Celsius.Next, inoculate a three milliliter preculture in YEPS-Light using a fresh plate. Incubate it for 24 hours on a rotating wheel at 28 degrees Celsius. The next day, add 25 microliters of the preculture to 50 milliliters of YEPS-Light in a baffled flask.Then, grow up the culture on an orbital shaker until it reaches the exponential phase. An optical density of 1.0 corresponds to one to two times 10 to the seventh cells in ustilago maydis. Check the optical density at 600 nanometers.A value of 0.6 to 1.0 is acceptable. Next, check the cells for contamination under 40x magnification. Bacterial contaminations can be identified as small and often moving cells.Fungal contaminations can be identified based on their shape or size. Always discard contaminated cultures and only work from clean ones. After pelleting the cells for five minutes at 1, 500 G, discard the supernantant.Then, re-suspend the pellet in 25 milliliters of SCS. Repeat the centrifugation. And meanwhile, prepare three milliliters of protoplasting solution per cell pellet.Pass this solution through a 22-micron filter. Now discard the supernatant and re-suspend the pellet in two milliliters of protoplasting solution. Then let the cells rest at room temperature until 30 to 40%of them are round or pinhead shaped.The reaction can take five to 20 minutes. Start observing it under the microscope after five minutes. To obtain the maximum transformation efficiency, the protoplastic reaction has to be stopped at the right moment.And then, the protoplasts have to be handled very carefully as if they were soap bubbles. Proceed with the protocol, always keeping the protoplasts on ice. The next step is to wash them with 10 milliliters of cold SCS, and then collect them with a five minute spin at 1, 000 G.Repeat this wash step a total of three times.After the washes, re-suspend the pellet in 10 milliliters of cold STC. Then collect the cells again with another five minute spin at 1, 000 G, followed by re-suspending them in 1 milliliter of cold STC. Now make 100 microliter aliquots in the cold tubes and store these aliquots at minus 80 degrees Celsius.To transform ustilago maydis protoplasts, prepare two selections per transformation. First, melt RegLight agar and cool it to 60 degrees Celsius. Then, to some of the melted agar, add the selective antibiotic at double the working concentration, and add 12 milliliters to each plate to form the bottom layer.The sample should be mixed carefully. Avoid making bubbles. Keep the remaining RegLight without antibiotics at 60 degrees Celsius.Next, thaw one tube of protoplasts on ice for each transformation. Once thawed, add one microliter of heparin solution and one microgram of linearized construct DNA. Then keep them on ice for 10 minutes.While waiting, spread 12 milliliters of RegLight without antibiotics over the RegLight with antibiotics. Next, add 500 microliters of STC/PEG to each transformation tube and carefully mix them with inversions. Then continue the incubation on ice for 15 more minutes.Now distribute each transformation reaction onto two separate selective RegLight plates. Make sure all the liquid has soaked into the plates before proceeding. Then, incubate the plates upright at 28 degrees Celsius for five to seven days to get 100 to 200 colonies.If only a few colonies grow, the protoplasts might contain too much cell wall, and this can be tested by transforming them with a cell-fabricating plasma or they might not be able to regenerate and this can be tested by planting them on plates without antibiotics. Later, select 24 transformants for testing. Re-purify them on selective YEPS-Light to obtain single colonies.On each plate, also streak out some of the original strain to make sure the antibiotics are selecting against non-transformants. It is critical to verify the mutations using a three step process that involves two PCRs and a Southern Blot analysis. These are detailed in the text protocol.This section explains how to prepare the genomic DNA needed for these analyses. First, inoculate five milliliters of YEPS-Light with the candidate transformant, and incubate it on a rotating wheel for 24 hours at 28 degrees Celsius. The next day, drop two microliters of the culture on a CM plate.Keep the culture sterile. Then prepare a two milliliter tube with about 200 microliters of hydrochloric acid-washed glass beads and two milliliters of the 24-hour culture. After spinning the tube at 12, 000 G for five minutes, aspirate and discard the supernatant.To the pellet, which may be frozen for storage, add 500 microliters of usti-lysis buffer two. Then shake the tube at 1, 000 RPM on a Vibrax for five to 15 minutes. Make sure that the cells are completely re-suspended, then incubate the tube at 65 degrees Celsius for 15 to 20 minutes.Next, place the tube on ice for five minutes. Once cooled down, add 100 microliters of 8 molar potassium acetate, and apply a brief vortex, or ten inversions. Next, spin the tube at 12, 000 G for 15 minutes at room temperature.Then, aliquot 500 microliters of the supernatant to a 1.5 milliliter tube, and add 400 microliters of isopropanol to the aliquot. After mixing, spin down the tube for five minutes at 12, 000 G.Discard the supernatant and wash the pelleted DNA with 500 microliters of 70%ethanol. Now apply a five minute spin and completely remove the supernatant.After another brief spin, let the DNA pellet air dry for a few minutes, and then add 50 microliters of RNase NTE. After adding the RNase, incubate with shaking, and then proceed to use the DNA for the analyses. Single and double mutants of the chintinases cts3 delta and multiple mutants with up to the three other chitinase genes were generated sequentially with the same constructs in two different genetic backgrounds.Transformants were confirmed by PCR and then by Southern Blot analysis. For the cts3 gene, the homologous recombination rate was 70%in the SG200 strain, suggesting cts3 has a non-essential function. Some of the mutations lead to obvious growth defects.For instance, the cts1/2 double mutant had a pronounced cell separation defect. Staining the septa showed that cytokinesis would complete, but the cells would remain connected. To test the contribution of chitinases to virulence, seedling infection assays were carried out using the SG200 strain mutants.While mutation of a controlled gene, khd4, reduced virulence, deletion of all the chitinases did not affect the infection of maize seedlings. After watching this video, you should have a good understanding of how to genetically modify smut fungi like ustilago maydis. Once mastered, strains can easily be generated in about four weeks.When using this procedure, it is really important to plan the strain verification detail by using future cloning programs. Do this before you start to work with fungal cultures. With slight modifications to this procedure, other smut fungi like sporsorium reilianum or ustilago esculenta or even filamentous fungi, like piriformospora indica, can be genetically modified.Don't forget that working with genetically modified organisms need to be carried out according to regulations in your country.

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JoVE Journal

Genetics

14.2K vistas.  Heinrich-Heine University Düsseldorf. The overall goal of this protocol is to genetically modify the smut fungus, ustilago maydis. This strain generation method allows functional characterization of genes in a variety of ways. For example, we can delete the genes, we can exchange the promotus, or we can generate fusion constructs.The main advantage of this method is that we can precisely verify the modification, so that any phenotype can be directly linked to the change in the gene of interest. Visual demonstration of this...