This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and future Planning (NRF-2018R1A2A1A05019892) to DC and by a grant from Plant Molecular Breeding Center (PMBC) of the Next Generation Biogreen 21 program of the Rural Development Administration (PJ013201) to EP.&#160;We thank the imaging center of the National Instrumentation Center for Environmental Management to provide a confocal microscope for filming.

Note: All steps are performed at room temperature, unless stated otherwise.
1. Preparation of Plant Materials (4 Weeks)
<ol>
	<li>Preparation for the N. benthamiana plants
	<ol>
		<li>Sow 2 seeds of N. benthamiana on the soil surface of each pot, cover the tray with a plastic dome, and allow seeds to germinate in a 25 &#176;C, 60% humidity growth chamber with a 16/8-h light/dark photoperiod cycle.</li>
		<li>After two weeks, pick out and discard the smallest seedling in eac...

<ol>
	<li>Melotto, M., Underwood, W., He, S. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+stomata+in+plant+innate+immunity+and+foliar+bacterial+diseases.">Role of stomata in plant innate immunity and foliar bacterial diseases.</a> Annu Rev Phytopathol. 46, 101-122 (2008).</li><li>Melotto, M., Underwood, W., Koczan, J., Nomura, K., He, S. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant+stomata+function+in+innate+immunity+against+bacterial+invasion.">Plant stomata function in innate immunity against bacterial invasion.</a> Cell. 126 (5), 969-980 (2006).</li><li>Toruno, T. Y., Stergiopoulos, I., Coaker, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant-Pathogen+Effectors:+Cellular+Probes+Interfering+with+Plant+Defenses+in+Spatial+and+Temporal+Manners.">Plant-Pathogen Effectors: Cellular Probes Interfering with Plant Defenses in Spatial and Temporal Manners.</a> Annu Rev Phytopathol. 54, 419-441 (2016).</li><li>Buttner, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Behind+the+lines-actions+of+bacterial+type+III+effector+proteins+in+plant+cells.">Behind the lines-actions of bacterial type III effector proteins in plant cells.</a> FEMS Microbiol Rev. 40 (6), 894-937 (2016).</li><li>Dewoody, R. S., Merritt, P. M., Marketon, M. M. <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+the+Yersinia+type+III+secretion+system:+traffic+control.">Regulation of the Yersinia type III secretion system: traffic control.</a> Front Cell Infect Microbiol. 3, 4 (2013).</li><li>Deng, W. L., Preston, G., Collmer, A., Chang, C. J., Huang, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+the+hrpC+and+hrpRS+operons+of+Pseudomonas+syringae+pathovars+syringae,+tomato,+and+glycinea+and+analysis+of+the+ability+of+hrpF,+hrpG,+hrcC,+hrpT,+and+hrpV+mutants+to+elicit+the+hypersensitive+response+and+disease+in+plants.">Characterization of the hrpC and hrpRS operons of Pseudomonas syringae pathovars syringae, tomato, and glycinea and analysis of the ability of hrpF, hrpG, hrcC, hrpT, and hrpV mutants to elicit the hypersensitive response and disease in plants.</a> J Bacteriol. 180 (17), 4523-4531 (1998).</li><li>Lewis, J. D., Guttman, D. S., Desveaux, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+targeting+of+plant+cellular+systems+by+injected+type+III+effector+proteins.">The targeting of plant cellular systems by injected type III effector proteins.</a> Semin Cell Dev Biol. 20 (9), 1055-1063 (2009).</li><li>Alfano, J. R., Collmer, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Type+III+secretion+system+effector+proteins:+double+agents+in+bacterial+disease+and+plant+defense.">Type III secretion system effector proteins: double agents in bacterial disease and plant defense.</a> Annu Rev Phytopathol. 42, 385-414 (2004).</li><li>Aung, K., Xin, X., Mecey, C., He, S. 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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+and+characterization+of+a+superfolder+green+fluorescent+protein.">Engineering and characterization of a superfolder green fluorescent protein.</a> Nat Biotechnol. 24 (1), 79-88 (2006).</li><li>Cabantous, S., Terwilliger, T. C., Waldo, G. 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The protocol described here is used for monitoring the accurate localization of the effector proteins injected by the bacterial T3SS into the host plant cell upon infection. Previously, the split GFP system was used as a tool to study the subcellular localization of mammalian proteins23,36, Salmonella T3E localization, and Agrobacterium VirE2 delivery through the T4SS into the plant cells37. To apply this system in the pl...

Plants are sessile organisms that encounter numerous invading pathogens including bacteria, fungi, viruses, insects, and nematodes throughout their life cycle. Among the phytopathogens, the gram-negative bacterial pathogens such as Pseudomonas spp. and Ralstonia spp., infect their host plants by entering through wounds or natural openings, such as the stomata and hydathode1. To successfully colonize host plants, bacterial pathogens have evolved to develop a variety of virulence factors2. When bacteria invade a host plant, they inject a series of virulence proteins &#8212; known as effectors &#8212; directly into the plant cells to promote their pathogenicity. These effectors suppress or modulate the plant innate immunity, and manipulate the host cellular processes to result in bacterial survival3.
Pathogenic bacteria mainly use a T3SS to deliver effector proteins directly into host cells4. The T3SS resembles a molecular syringe with a needle-like channel connecting from a scaffold protein structure across the inner and the outer bacterial membranes to the injection site of the host cell5. This T3SS-mediated effector (T3E) secretion mechanism is well-conserved in various gram-negative bacterial pathogens of the plant as well as human. One of the representative plant pathogens, the P. syringae pv. Tomato DC3000 hrcC mutant which typically has a defective T3SS, has restricted growth in plants likely due to the inability of this mutant to fully suppress the plant immunity (by injecting effector proteins)6. Upon translocation into the host cells, effectors target various host proteins that are important for the host cell system, including plant defense responses, gene transcription, cell death, proteasome, vesicle trafficking, and hormone pathways7,8,9,10. Therefore, tracking of the cellular localization of the effector proteins in the host cells is an attractive target to understand their functions with respect to modulation of the plant immunity.
Most of the localization studies of the T3Es have employed Agrobacterium-mediated overexpression with a large fluorescence protein in the host plant9. However, the heterologous expression method for genes that are introduced in other species has been shown to be mis-localized or occasionally non-functional11,12,13. In addition, several studies revealed that bacterial effectors undergo modification for proper targeting in the host cells14,15,16,17. Therefore, transiently expressed effectors in the cytosol of the plant cells may not be functionally or quantitatively identical to the effectors which are delivered by the T3SS upon pathogen infection18. Moreover, the fusion of large fluorescent tags to effector proteins may disrupt the proper effector delivery and visualization18,19. Therefore, these approaches to assay the T3E function may not fully reflect the native localization of the T3SS-secreted effectors.
A green fluorescent protein (GFP) is composed of an 11-stranded &#946;-barrel enclosing a central strand that includes a chromophore20. Waldo et al. reported a novel split-GFP system that consists of a small component (GFP &#946; strand 11; GFP11) and a large complementary fragment (GFP &#946; strand 1-10; GFP1-10)21. The fragments do not fluoresce by themselves but fluoresce upon their self-association when both fragments are in close proximity with each other. For the optimization of the protein folding efficiency, robust folding variants of the GFP, i.e., sfGFP and sfGFPOPT, were subsequently developed for the split GFP system20,21,22. Recently, single amino acid mutated variants of sfGFP1-10OPT- sfYFP1-10OPT and sfCFP1-10OPT- that can reconstitute with a sfGFP11 fragment, and show yellow and cyan fluorescence respectively, were generated23. Moreover, sfCherry, a derivative of mCherry, can be split into sfCherry1-10 and sfCherry11 fragments in the same manner as sfGFP23.
This system has been adapted to label and track the T3SS effectors in HeLa cells during infection using the effectors from Salmonella24. However, it was previously not optimized for the host plant-bacterial pathogen system. Recently, we optimized the split GFP system based on the improved sfGFP1-10OPT to monitor the subcellular localization of the T3Es delivered from P. syringae into plant cells25. To facilitate the localization studies of the T3Es to different subcellular compartments in the plant cells, a set of transgenic Arabidopsis thaliana plants were generated to express sfGFP1-10OPT in the various subcellular compartments25. Moreover, the plasmids carrying a variety of organelle-targeted sfGFP1-10OPT for the Agrobacterium-mediated transient overexpression and the sfGFP11-tagged vectors for the T3SS-based effector delivery were also generated. The seeds of various transgenic Arabidopsis lines and the plasmids to express the T3Es of interest can be obtained from sources mentioned in the Table of Materials26,27.
In the following protocol, we describe an optimized system to monitor the dynamics of effectors delivered by bacteria in the host cells using the split sfGFP system. Infection of plants expressing sfGFP1-10OPT with transgenic Pseudomonas carrying recombinant sfGFP11 plasmid results in a delivery of the sfGFP11-tagged effector from Pseudomonas into the host cell. Consequently, these proteins are reconstituted and translocate to the specific effector target compartment(s). The Pseudomonas syringae pv. tomato CUCPB5500 strain in which 18 effectors are deleted, was used because this strain showed low or no cell death in both A. thaliana and N. benthamianas28. However, all of the materials and steps described here can be replaced or modified to adapt the split sfGFP system for investigation of other biological questions or optimization in the given laboratory conditions.

<table>
	<tbody>
		<tr>
			<td>Arabidopsis transgenic lines</td>
			<td></td>
			<td></td>
			<td>Park, E., Lee, H. Y., Woo, J., Choi, D. &#38; Dinesh-Kumar, S. P. Spatiotemporal Monitoring of Pseudomonas syringae Effectors via Type III Secretion Using Split Fluorescent Protein Fragments. Plant Cell. 29 (7), 1571-1584 (2017)</td>
		</tr>
		<tr>
			<td>CYTO-sfGFP1-10</td>
			<td>ABRC</td>
			<td>CS69831</td>
			<td></td>
		</tr>
		<tr>
			<td>NU-sfGFP1-10</td>
			<td>ABRC</td>
			<td>CS69832</td>
			<td></td>
		</tr>
		<tr>
			<td>PT-sfGFP1-10</td>
			<td>ABRC</td>
			<td>CS69833</td>
			<td></td>
		</tr>
		<tr>
			<td>MT-sfGFP1-10</td>
			<td>ABRC</td>
			<td>CS69834</td>
			<td></td>
		</tr>
		<tr>
			<td>PX-sfGFP1-10</td>
			<td>ABRC</td>
			<td>CS69835</td>
			<td></td>
		</tr>
		<tr>
			<td>ER-sfGFP1-10</td>
			<td>ABRC</td>
			<td>CS69836</td>
			<td></td>
		</tr>
		<tr>
			<td>GO-sfGFP1-10</td>
			<td>ABRC</td>
			<td>CS69837</td>
			<td></td>
		</tr>
		<tr>
			<td>PM-sfGFP1-10</td>
			<td>ABRC</td>
			<td>CS69838</td>
			<td></td>
		</tr>
		<tr>
			<td>Organelle-targeted sfGFP1-10OPT plasmid</td>
			<td></td>
			<td></td>
			<td>Park, E., Lee, H. Y., Woo, J., Choi, D. &#38; Dinesh-Kumar, S. P. Spatiotemporal Monitoring of Pseudomonas syringae Effectors via Type III Secretion Using Split Fluorescent Protein Fragments. Plant Cell. 29 (7), 1571-1584 (2017)</td>
		</tr>
		<tr>
			<td>CYTO-sfGFP1-10</td>
			<td>Addgene</td>
			<td>97387</td>
			<td></td>
		</tr>
		<tr>
			<td>NU-sfGFP1-10</td>
			<td>Addgene</td>
			<td>97388</td>
			<td></td>
		</tr>
		<tr>
			<td>PT-sfGFP1-10</td>
			<td>Addgene</td>
			<td>97389</td>
			<td></td>
		</tr>
		<tr>
			<td>MT-sfGFP1-10</td>
			<td>Addgene</td>
			<td>97390</td>
			<td></td>
		</tr>
		<tr>
			<td>PX-sfGFP1-10</td>
			<td>Addgene</td>
			<td>97391</td>
			<td></td>
		</tr>
		<tr>
			<td>ER-sfGFP1-10</td>
			<td>Addgene</td>
			<td>97392</td>
			<td></td>
		</tr>
		<tr>
			<td>GO-sfGFP1-10</td>
			<td>Addgene</td>
			<td>97393</td>
			<td></td>
		</tr>
		<tr>
			<td>PM-sfGFP1-10</td>
			<td>Addgene</td>
			<td>97394</td>
			<td></td>
		</tr>
		<tr>
			<td>ER-sfCherry1-10</td>
			<td>Addgene</td>
			<td>97403</td>
			<td></td>
		</tr>
		<tr>
			<td>ER-sfYFP1-10</td>
			<td>Addgene</td>
			<td>97404</td>
			<td></td>
		</tr>
		<tr>
			<td>CYTO-sfCFP1-10</td>
			<td>Addgene</td>
			<td>97405</td>
			<td></td>
		</tr>
		<tr>
			<td colspan="3">sfGFP11-tagged Gateway compatible vector for T3SS-based effector delivery system</td>
			<td>Park, E., Lee, H. Y., Woo, J., Choi, D. &#38; Dinesh-Kumar, S. P. Spatiotemporal Monitoring of Pseudomonas syringae Effectors via Type III Secretion Using Split Fluorescent Protein Fragments. Plant Cell. 29 (7), 1571-1584 (2017)</td>
		</tr>
		<tr>
			<td>pBK-GW-1-2</td>
			<td>Addgene</td>
			<td>98250</td>
			<td>pAvrRpm1:GW:HA-sfGFP11:AvrRpm1t; Resistant to Kanamycin (25 ug/ml)</td>
		</tr>
		<tr>
			<td>pBK-GW-1-4</td>
			<td>Addgene</td>
			<td>98251</td>
			<td>pAvrRpm1:GW:HA-2xsfGFP11:AvrRpm1t; Resistant to Kanamycin (25 ug/ml)</td>
		</tr>
		<tr>
			<td>pBK-GW-2-2</td>
			<td>Addgene</td>
			<td>98252</td>
			<td>pAvrRpm1:AvrRPM1sp:GW:HA-sfGFP11:AvrRpm1t; Resistant to Kanamycin (25 ug/ml)</td>
		</tr>
		<tr>
			<td>pBK-GW-2-4</td>
			<td>Addgene</td>
			<td>98253</td>
			<td>pAvrRpm1:AvrRPM1sp:GW:HA-2xsfGFP11:AvrRpm1t; Resistant to Kanamycin (25 ug/ml)</td>
		</tr>
		<tr>
			<td>pBG-GW-1-2</td>
			<td>Addgene</td>
			<td>98254</td>
			<td>pAvrRpm1:GW:HA-sfGFP11:AvrRpm1t; Resistant to Gentamycin (25 ug/ml)</td>
		</tr>
		<tr>
			<td>pBG-GW-1-4</td>
			<td>Addgene</td>
			<td>98255</td>
			<td>pAvrRpm1:GW:HA-2xsfGFP11:AvrRpm1t; Resistant to Gentamycin (25 ug/ml)</td>
		</tr>
		<tr>
			<td>pBG-GW-2-2</td>
			<td>Addgene</td>
			<td>98256</td>
			<td>pAvrRpm1:AvrRPM1sp:GW:HA-sfGFP11:AvrRpm1t; Resistant to Gentamycin (25 ug/ml)</td>
		</tr>
		<tr>
			<td>pBG-GW-2-4</td>
			<td>Addgene</td>
			<td>98257</td>
			<td>pAvrRpm1:AvrRPM1sp:GW:HA-2xsfGFP11:AvrRpm1t; Resistant to Gentamycin (25 ug/ml)</td>
		</tr>
		<tr>
			<td>Bacterial strains</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Agrobacterium tumefaciens GV3101</td>
			<td></td>
			<td></td>
			<td>Csaba Koncz and Jeff Schell, The promoter of TL-DNA gene 5 controls the tissue-specific expression of chimaeric genes carried by a novel type of Agrobacterium binary vector. Mol Gen Genet. 204,383-396 (1986); Resistant to gentamycin (50 ug/ml) and rifampicin (50 ug/ml)</td>
		</tr>
		<tr>
			<td>Pseudomonas syringae pv. Tomato CUCPB5500</td>
			<td></td>
			<td></td>
			<td>Kvitko, B. H. et al. Deletions in the repertoire of Pseudomonas syringae pv. tomato DC3000 type III secretion effector genes reveal functional overlap among effectors. PLoS Pathog. 5 (4) (2009).; Resistant to rifampicin (100 ug/ml)</td>
		</tr>
		<tr>
			<td>Media components</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Plant germination media</td>
			<td></td>
			<td></td>
			<td>Add 2.165g/L Murashige &#38; Skoog powder, 10 g/L sucrose to water. Adjust to pH 5.8 and add 2.2 g/L phytagel. Autocalve.</td>
		</tr>
		<tr>
			<td>Murashige &#38; Skoog medium including vitamins</td>
			<td>Duchefa Biochemie</td>
			<td>M0222</td>
			<td>Store at 4 &#176;C.</td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Duchefa Biochemie</td>
			<td>S0809</td>
			<td></td>
		</tr>
		<tr>
			<td>Phytagel</td>
			<td>Sigma-Aldrich</td>
			<td>P8169</td>
			<td></td>
		</tr>
		<tr>
			<td>LB media</td>
			<td></td>
			<td></td>
			<td>Add 10 g/L tryptone, 5 g/L yeast extract, 10 g/L NaCl to water. For solid media, add 15 g/L micro agar. Autoclave.&#160; Allow solution to cool to 55 &#176;C, and add antibiotic if needed.</td>
		</tr>
		<tr>
			<td>Tryptone</td>
			<td>BD Bioscience</td>
			<td>211705</td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast extract</td>
			<td>BD Bioscience</td>
			<td>212750</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Duchefa Biochemie</td>
			<td>S0520</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro agar</td>
			<td>Duchefa Biochemie</td>
			<td>M1002</td>
			<td></td>
		</tr>
		<tr>
			<td>King&#39;s B media</td>
			<td></td>
			<td></td>
			<td>10 g/L protease peptone #2, 1.5 g/L anhydrous K2HPO4, 15 g/L of agar to water. Autoclave. Cool down to 55 &#176;C and add sterile 15 ml/L glycerol, 5 ml/L MgSO4 to the medium. Add antibiotics if needed.</td>
		</tr>
		<tr>
			<td>Proteose peptone</td>
			<td>BD Bioscience</td>
			<td>212120</td>
			<td></td>
		</tr>
		<tr>
			<td>Anhydrous K2HPO4</td>
			<td>Sigma-Aldrich</td>
			<td>1551128 USP</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Duchefa Biochemie</td>
			<td>G1345</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4</td>
			<td>Sigma-Aldrich</td>
			<td>M7506</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto Agar</td>
			<td>BD Bioscience</td>
			<td>214010</td>
			<td></td>
		</tr>
		<tr>
			<td>Mannitol-Glutamate (MG) liquid media </td>
			<td></td>
			<td></td>
			<td>Add 10 g/L of mannitol, 2 g/L of L-glutamic acid, 0.5 g/L of KH2PO4, 0.2 g/L of NaCl, and 0.2 g/L of MgSO4 to water. Adjust to pH 7</td>
		</tr>
		<tr>
			<td>Mannitol</td>
			<td>Duchefa Biochemie</td>
			<td>M0803</td>
			<td></td>
		</tr>
		<tr>
			<td>L-glutamic acid</td>
			<td>Duchefa Biochemie</td>
			<td>G0707</td>
			<td></td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Sigma-Aldrich</td>
			<td>NIST200B</td>
			<td></td>
		</tr>
		<tr>
			<td>Infiltration buffer</td>
			<td></td>
			<td></td>
			<td>10 mM MES (2-(N-morpholino)-ethane sulfonic acid), 10 mM MgCl2, 150 &#181;M acetosyringone. pH 5.6; Prepare a fresh buffer before use.</td>
		</tr>
		<tr>
			<td>MES</td>
			<td>Duchefa Biochemie</td>
			<td>M1503</td>
			<td>Prepare 100 mM (pH 5.6) stock in water. Filter sterilize.</td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Sigma-Aldrich</td>
			<td>M8266</td>
			<td>Prepare 100 mM stock in water. Autoclave.</td>
		</tr>
		<tr>
			<td>Acetosyringone</td>
			<td>Sigma-Aldrich</td>
			<td>D134406</td>
			<td>Prepare 150 mM stock in DMSO.</td>
		</tr>
		<tr>
			<td>Confocal microscope equipments/materials</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>710 laser scanning confocal system</td>
			<td>Carl Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Axio observer Z1 inverted microscope</td>
			<td>Carl Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Propidium iodide</td>
			<td>ThermoFisher</td>
			<td>P1304MP</td>
			<td></td>
		</tr>
	</tbody>
</table>

split green fluorescent protein system to visualize effectors delivered from bacteria during infection

Bacteria, one of the most important causative agents of various plant diseases, secrete a set of effector proteins into the host plant cell to subvert the plant immune system. During infection cytoplasmic effectors are delivered to the host cytosol via a type III secretion system (T3SS). After delivery into the plant cell, the effector(s) targets the specific compartment(s) to modulate host cell processes for survival and replication of the pathogen. Although there has been some research on the subcellular localization of effector proteins in the host cells to understand their function in pathogenicity by using fluorescent proteins, investigation of the dynamics of effectors directly injected from bacteria has been challenging due to the incompatibility between the T3SS and fluorescent proteins.
Here, we describe our recent method of an optimized split superfolder green fluorescent protein system (sfGFPOPT) to visualize the localization of effectors delivered via the bacterial T3SS in the host cell. The sfGFP11 (11th &#946;-strand of sfGFP)-tagged effector secreted through the T3SS can be assembled with a specific organelle targeted sfGFP1-10OPT (1-10th &#946;-strand of sfGFP) leading to fluorescence emission at the site. This protocol provides a procedure to visualize the reconstituted sfGFP fluorescence signal with an effector protein from Pseudomonas syringae in a particular organelle in the Arabidopsis and Nicotiana benthamiana plants.

The &#946;-barrel structure of GFP is composed of eleven &#946; strands and can be divided into two fragments, the 1 - 10th strand (GFP1-10OPT) and the 11th (GFP11) strand. Although neither of two fragments fluorescent by themselves, self-assembled sfGFP can emit the fluorescence when the two fragments exist in close proximity (Figure 1A). In this system, sfGFP1-10OPT-expressing Arabidopsis or N. bentha...

Watch this Scientific Journal Video about Split Green Fluorescent Protein System to Visualize Effectors Delivered from Bacteria During Infection at JoVE.com

Split Green Fluorescent Protein System to Visualize Effectors Delivered from Bacteria During Infection

Fluorescent protein-based approaches to monitor effectors secreted by bacteria into host cells are challenging. This is due to the incompatibility between fluorescent proteins and the type-III secretion system. Here, an optimized split superfolder GFP system is used for visualization of effectors secreted by bacteria into the host plant cell.

Bacteria, one of the most important causative agents of various plant diseases, secrete a set of effector proteins into the host plant cell to subvert the ...

This method can help answer key questions in the plant-microbe interaction field such as how pathogenic bacteria can disturb the optimal condition of their host plant cells by using proteins called effectors secreted into plant cells. The main advantage of this technique is the bacterial effector protein is expressed in the bacterial cell using their native expression system and then delivered to the plant cell through the bacterial type III secretion system. To begin this procedure, prepare Nicotiana benthamiana and Arabidopsis thaliana plants as outlined in the text protocol.Next, use standard electroporation to transform the plasmid carrying and effector gene fused to the sfGFP11 tag to Pseudomonas syringae pathovar tomato CUCPB5500 strain. The optimal time point and expression level, or reconstitute sfGFP, really depends on your effector protein. We recommend to optimize inoculation or observation conditions.Gently spread the transformed bacterial cells over the surface of King's B Agar plates. Then incubate the plates at 28 degrees Celsius for two days. After this, inoculate one bacterial colony into King's B liquid medium with an antibiotic appropriate for the vector.Incubate overnight at 28 degrees Celsius with shaking at 200 rpm. The next day, add autoclaved glycerol to the inoculated medium to a final concentration of 50%Store at negative 80 degrees Celsius. To begin, transform the plasmid into Agrobacterium tumefaciens strain GV3101 cells as outlined in the text protocol.Grow the cells on supplemented LB Agar medium at 28 degrees Celsius for two days. Using a single colony from the LB Agar medium, inoculate 5 milliliters of supplemented liquid LB medium. Then, grow the cells overnight at 28 degrees Celsius with shaking at 200 rpm.After this, centrifuge at 3000 G for 10 minutes to harvest the cells. Pour off the supernatant and re-suspend the pellet in 1 milliliter of freshly made infiltration buffer. Using a spectrophotometer, determine the quantity of Agrobacterium cells by measuring the optical density value at an absorbance of 600 nanometers.Then, use infiltration buffer to adjust the OD 600 of the bacterial cells to 0.5. Leave the culture on a gentle rocker at room temperature for one-to-five hours. To infiltrate the leaves, use 10-microliter pipette tip to poke a hole in the center of each leaf.Use a needleless 1-milliliter syringe to carefully inject 500 microliters of the Agrobacterium suspension into the adaxial side of the leaf. Wipe the remaining bacterial suspension off of the leaves and mark the boundary of the infiltrated region. Keep the infiltrated plants in a growth chamber at 25 degrees Celsius and 60%humidity for two days.Streak the transformed Pseudomonas strain from the glycerol stock onto King's B Agar medium with the appropriate antibiotic. Incubate at 28 degrees Celsius for two days. Inoculate a loop of Pseudomonas cells in mannitol glutamate liquid medium.Incubate the culture overnight at 28 degrees Celsius with shaking at 200 rpm. After this, centrifuge at 3000 G for 10 minutes to harvest the cells. Pour off the supernatant and re-suspend the pellet in 10-millimolar magnesium chloride solution.Then, adjust the optical density to 0.02 for Nicotiana benthamiana leaves and to 0.002 for Arabidopsis leaves. For the Nicotiana benthamiana leaves, infiltrate the Pseudomonas suspension into the same area as the Agrobacterium was infiltrated two days earlier. For the transgenic Arabidopsis, infiltrate the Pseudomonas suspension into two four-week-old short day-grown leaves.Finally, cut out a leaf disk for the Pseudomonas-inoculated leaves. At specific time points after infiltration of Pseudomonas, use a confocal laser scanning system to image two, two square centimeter leaf disks from the single plant. Observe the cells away from the infiltration hole to avoid dead cells killed by wounding.Translocated effectors from the bacteria are present only in very small amounts. Therefore, you may increase the laser power and gain a fluorescence emission to detect a fluorescent signal. However, don't overpower to avoid capturing false signal from autofluorescence from the plant cells.In this study, a fluorescent protein-based approach is used to monitor effectors secreted by bacteria into host cells. A confocal laser scan of a Nicotiana benthamiana leaf three hours after infection is shown here. Cells expressing optimized sfGFP with AvrB only do not show any fluorescent signal.However, GFP signals are seen from the infected cells containing AvrB, sfGFP11. This verifies that AvrB sfGFP11 complex is reconstituted with optimized sfGFP in the cytosol and then translocates to the plasma membrane. While attempting this procedure, it's important to remember to keep the plant materials healthy and to prepare fresh bacteria culture for active cells.Following this procedure, other methods like resin blood analysis can be preponed to understand false translation modification of bacteria effector proteins in plant cells during plant immune responses. After watching this video, you should have a good understanding of how to visualize the type III effector delivery in infected plant cells. Plant materials and bacteria cultures should be disposed of following your lab's criteria for biohazardous waste and don't forget to wear your PPE.

split-green-fluorescent-protein-system-to-visualize-effectors

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Biology

10.2K vistas.  Seoul National University. This method can help answer key questions in the plant-microbe interaction field such as how pathogenic bacteria can disturb the optimal condition of their host plant cells by using proteins called effectors secreted into plant cells. The main advantage of this technique is the bacterial effector protein is expressed in the bacterial cell using their native expression system and then delivered to the plant cell through the bacterial type III secretion system. To begin this procedure, prepare ...