An Efficient Method for Quantitative, Single-cell Analysis of Chromatin Modification and Nuclear Architecture in Whole-mount Ovules in <em>Arabidopsis</em>

In flowering plants, the somatic-to-reproductive cell fate transition is marked by the specification of spore mother cells (SMCs) in floral organs of the ...

Université de Montpellier II

Some angiosperms reproduce by apomixis, a natural way of cloning through seeds. Apomictic plants bypass both meiosis and egg cell fertilization, producing progeny that are genetic replicas of the mother plant. In this report, we analyze reproductive development in Tripsacum dactyloides, an apomictic relative of maize, and in experimental apomictic hybrids between maize and Tripsacum. We show that apomictic reproduction is characterized by an alteration of developmental timing of both sporogenesis and early embryo development. The absence of female meiosis in apomictic Tripsacum results from an early termination of female meiosis. Similarly, parthenogenetic development of a maternal embryo in apomicts results from precocious induction of early embryogenesis events. We also show that male meiosis in apomicts is characterized by comparable asynchronous expression of developmental stages. Apomixis thus results in an array of possible phenotypes, including wild-type sexual development. Overall, our observations suggest that apomixis in Tripsacum is a heterochronic phenotype; i.e., it relies on a deregulation of the timing of reproductive events, rather than on the alteration of a specific component of the reproductive pathway.

Heterochronic expression of sexual reproductive programs during apomictic development in Tripsacum.

In animals, early embryonic development is largely dependent on maternal transcripts synthesized during gametogenesis. Recent data in plants also suggest maternal control over early seed development, but the actual timing of zygotic genome activation is unclear. Here, we analyzed the timing of the maternal-to-zygotic transition during early Zea mays seed development. We show that for 16 genes expressed during early seed development, only maternally inherited alleles are detected during 3 d after fertilization in both the embryo and the endosperm. Microarray analyses of precocious embryonic development in apomictic hybrids between maize and its wild relative, Tripsacum, demonstrate that early embryo development occurs without significant quantitative changes to the transcript population in the ovule before fertilization. Precocious embryo development is also correlated with a higher proportion of polyadenylated mRNA in the ovules. Our data suggest that the maternal-to-zygotic transition occurs several days after fertilization. By contrast, novel transcription accompanies early endosperm development, indicating that different mechanisms are involved in the initiation of endosperm and embryo development.

Timing of the maternal-to-zygotic transition during early seed development in maize.

Apomixis in plants covers a variety of cloning systems through seeds of great potential for plant breeding. Among long-standing approaches for crop improvement is the attempt to exploit wild relatives as natural, vast reservoirs for novel genetic variation. With regard to apomixis, maize possesses an apomictic wild relative, Tripsacum, which we used to produce advanced maize-Tripsacum hybrid generations. However, introgression of apomixis in maize has failed so far. In order to understand the hows and whys, we undertook characterization of seed development and inheritance studies in these materials. We show that apomictic seeds suffer from epigenetic loads. Both seed tissues, the endosperm and the embryo, displayed developmental defects resulting from imbalanced parental genomic contributions and aberrant methylation patterns, respectively. Progeny characterization of several maize-Tripsacum hybrid generations allowed significant progress toward the unraveling of the genetics of apomixis. First, chromosome deletion mapping showed that expression of apomixis requires one single Tripsacum chromosome. However, inheritance studies revealed that female gametes inheriting this segment were unequivalent carriers depending on their origin: unreduced gametes transmit a functional segment, whereas progeny derived from reduced ones reproduced sexually. Finally, chromosomal or genomic dosage variation barely affected the apomictic phenotype suggesting no dependency for ploidy in these materials. We conclude that epigenetic information imposes constraints for apomictic seed development and seems pivotal for transgenerational propagation of apomixis. The nature of the triggering mechanisms remains unknown as-yet, but it certainly explains the modest success relative to the development of apomictic maize thus far.

Seed development and inheritance studies in apomictic maize-Tripsacum hybrids reveal barriers for the transfer of apomixis into sexual crops.

Whether deposited maternal products are important during early seed development in flowering plants remains controversial. Here, we show that RNA interference-mediated downregulation of transcription is deleterious to endosperm development but does not block zygotic divisions. Furthermore, we show that RNA POLYMERASE II is less active in the embryo than in the endosperm. This dimorphic pattern is established late during female gametogenesis and is inherited by the two products of fertilization. This juxtaposition of distinct transcriptional activities correlates with differential patterns of histone H3 lysine 9 dimethylation, LIKE HETEROCHROMATIN PROTEIN1 localization, and Histone H2B turnover in the egg cell versus the central cell. Thus, distinct epigenetic and transcriptional patterns in the embryo and endosperm are already established in their gametic progenitors. We further demonstrate that the non-CG DNA methyltransferase CHROMOMETHYLASE3 (CMT3) and DEMETER-LIKE DNA glycosylases are required for the correct distribution of H3K9 dimethylation in the egg and central cells, respectively, and that plants defective for CMT3 activity show abnormal embryo development. Our results provide evidence that cell-specific mechanisms lead to the differentiation of epigenetically distinct female gametes in Arabidopsis thaliana. They also suggest that the establishment of a quiescent state in the zygote may play a role in the reprogramming of the young plant embryo.

Embryo and endosperm inherit distinct chromatin and transcriptional states from the female gametes in Arabidopsis.

Si les produits maternelles d&eacute;pos&eacute;s sont importants au cours du d&eacute;veloppement pr&eacute;coce de la graine chez les angiospermes demeure controvers&eacute;e. Ici, nous montrons que RNA m&eacute;di&eacute;e par l&#39;interf&eacute;rence la r&eacute;gulation n&eacute;gative de la transcription est nuisible au d&eacute;veloppement de l&#39;endosperme, mais ne bloque pas les divisions zygotiques. De plus, nous montrons que l&#39;ARN polym&eacute;rase II est moins actif dans l&#39;embryon que dans l&#39;endosperme. Ce mod&egrave;le dimorphique est &eacute;tabli tardivement au cours de la gam&eacute;togen&egrave;se femelle et est h&eacute;rit&eacute; par les deux produits de fertilisation. Cette juxtaposition d&#39;activit&eacute; transcriptionnelle distincte est corr&eacute;l&eacute;e avec des mod&egrave;les diff&eacute;rentiels de l&#39;histone H3 lysine 9 MBD, comme H&Eacute;T&Eacute;ROCHROMATINE PROTEIN1 localisation et Histone H2B chiffre d&#39;affaires dans l&#39;oosph&egrave;re et la cellule centrale. Ainsi, les profils &eacute;pig&eacute;n&eacute;tiques et transcriptionnelles distincts dans l&#39;embryon et l&#39;endosperme sont d&eacute;j&agrave; &eacute;tablis dans leurs prog&eacute;niteurs gam&eacute;tiques. De plus, nous d&eacute;montrons que la non - CG ADN m&eacute;thyltransf&eacute;rase CHROMOMETHYLASE3 (CMT3) et DEMETER-LIKE DNA glycosylases sont n&eacute;cessaires pour la bonne distribution de MBD H3K9 dans le &oelig;uf et les cellules centrales, respectivement, et plantes d&eacute;fectueuses pour activit&eacute; de CMT3 montrant le d&eacute;veloppement anormal de l&#39;embryon. Nos r&eacute;sultats d&eacute;montrent que des m&eacute;canismes cellulaires sp&eacute;cifiques conduisent &agrave; la diff&eacute;renciation des &eacute;pig&eacute;n&eacute;tiques distincts gam&egrave;tes femelles chez Arabidopsis thaliana. Ils sugg&egrave;rent &eacute;galement que la cr&eacute;ation d&#39;un &eacute;tat de repos dans le zygote peut jouer un r&ocirc;le dans la reprogrammation de l&#39;embryon du jeune plant.

Embryon et l&#39;endosperme h&eacute;ritent de chromatine distincte et &Eacute;tats transcriptionnelles des gam&egrave;tes femelles chez Arabidopsis.

Se depositate prodotti materne sono importanti durante lo sviluppo iniziale di sementi di piante fiorite rimane controversa. Qui, vi mostriamo che RNA interference-mediata downregulation della trascrizione &egrave; deleteria per lo sviluppo di endosperma ma non bloccare divisioni zygotic. Inoltre, mostriamo che la RNA POLIMERASI II &egrave; meno attivo nell&#39;embrione rispetto all&#39;endosperma. Questo modello dimorfici &egrave; stabilito in ritardo durante gametogenesis femminile e viene ereditato da due prodotti di fecondazione. Questa giustapposizione di distinte attivit&agrave; transcriptional correla con modelli differenziali dell&#39;istone H3 lisina 9 dimethylation, come ETEROCROMATINA PROTEIN1 localizzazione e istone H2B fatturato nella cellula uovo rispetto alla cella centrale. Cos&igrave;, distinti modelli epigenetici e transcriptional nell&#39;embrione ed endosperma sono gi&agrave; stabiliti nel loro progenitori gametic. Noi dimostrare ulteriormente che il methyltransferase del DNA CG CHROMOMETHYLASE3 (CMT3) e DEMETER-LIKE DNA glycosylases sono necessari per la corretta distribuzione di H3K9 dimethylation nell&#39;uovo e le cellule centrali, rispettivamente, e che impianti difettosi per attivit&agrave; CMT3 mostrano lo sviluppo embrionale anormale. I nostri risultati forniscono prove che cella specifici meccanismi portano alla differenziazione dei gameti femminili epigeneticamente distinti in Arabidopsis thaliana. Essi suggeriscono anche che l&#39;istituzione di uno stato quiescente nello zigote pu&ograve; svolgere un ruolo nella riprogrammazione dell&#39;embrione giovane pianta.

Embrione ed endosperma ereditano distinta della cromatina e stati transcriptional da gameti femminili in Arabidopsis.

In the ovules of most sexual flowering plants female gametogenesis is initiated from a single surviving gametic cell, the functional megaspore, formed after meiosis of the somatically derived megaspore mother cell (MMC). Because some mutants and certain sexual species exhibit more than one MMC, and many others are able to form gametes without meiosis (by apomixis), it has been suggested that somatic cells in the ovule are competent to respond to a local signal likely to have an important function in determination. Here we show that the Arabidopsis protein ARGONAUTE 9 (AGO9) controls female gamete formation by restricting the specification of gametophyte precursors in a dosage-dependent, non-cell-autonomous manner. Mutations in AGO9 lead to the differentiation of multiple gametic cells that are able to initiate gametogenesis. The AGO9 protein is not expressed in the gamete lineage; instead, it is expressed in cytoplasmic foci of somatic companion cells. Mutations in SUPPRESSOR OF GENE SILENCING 3 and RNA-DEPENDENT RNA POLYMERASE 6 exhibit an identical defect to ago9 mutants, indicating that the movement of small RNA (sRNAs) silencing out of somatic companion cells is necessary for controlling the specification of gametic cells. AGO9 preferentially interacts with 24-nucleotide sRNAs derived from transposable elements (TEs), and its activity is necessary to silence TEs in female gametes and their accessory cells. Our results show that AGO9-dependent sRNA silencing is crucial to specify cell fate in the Arabidopsis ovule, and that epigenetic reprogramming in companion cells is necessary for sRNA-dependent silencing in plant gametes.

Control of female gamete formation by a small RNA pathway in Arabidopsis.

During embryogenesis there is a major switch from dependence upon maternally-deposited products to reliance on products of the zygotic genome. In animals, this so-called maternal-to-zygotic transition occurs following a period of transcriptional quiescence. Recently, we have shown that the early embryo in Arabidopsis is also quiescent, a state inherited from the female gamete and linked to specific patterns of H3K9 dimethylation and TERMINAL FLOWER2 (TFL2) localization. We also demonstrated that CHROMOMETHYLASE 3 (CMT3) is required for H3K9 dimethylation in the egg cell and for normal embryogenesis during the first few divisions of the zygote. Subsequent analysis of CMT3 mutants points to a key role in egg cell reprogramming by controlling silencing in both transposon and euchromatic regions. A speculative model of the CMT3-induced egg cell silencing is presented here, based on these results and current data from the literature suggesting the potential involvement of small RNAs targeted to the egg cell, a process conceptually similar to the division of labor described in the male gametophyte for which we show that H3K9 modifications and TFL2 localization are reminiscent of the female gametophyte.

A role for CHROMOMETHYLASE3 in mediating transposon and euchromatin silencing during egg cell reprogramming in Arabidopsis.

Apomictic plants reproduce asexually through seeds by avoiding both meiosis and fertilization. Although apomixis is genetically regulated, its core genetic component(s) has not been determined yet. Using profiling experiments comparing sexual development in maize (Zea mays) to apomixis in maize-Tripsacum hybrids, we identified six loci that are specifically downregulated in ovules of apomictic plants. Four of them share strong homology with members of the RNA-directed DNA methylation pathway, which in Arabidopsis thaliana is involved in silencing via DNA methylation. Analyzing loss-of-function alleles for two maize DNA methyltransferase genes belonging to that subset, dmt102 and dmt103, which are downregulated in the ovules of apomictic plants and are homologous to the Arabidopsis CHROMOMETHYLASEs and DOMAINS REARRANGED METHYLTRANSFERASE families, revealed phenotypes reminiscent of apomictic development, including the production of unreduced gametes and formation of multiple embryo sacs in the ovule. Loss of DMT102 activity in ovules resulted in the establishment of a transcriptionally competent chromatin state in the archesporial tissue and in the egg cell that mimics the chromatin state found in apomicts. Interestingly, dmt102 and dmt103 expression in the ovule is found in a restricted domain in and around the germ cells, indicating that a DNA methylation pathway active during reproduction is essential for gametophyte development in maize and likely plays a critical role in the differentiation between apomictic and sexual reproduction.

Inactivation of a DNA methylation pathway in maize reproductive organs results in apomixis-like phenotypes.

Apomixis is a form of asexual reproduction through seeds in angiosperms. Apomictic plants bypass meiosis and fertilization, developing offspring that are genetically identical to their mother. In a genetic screen for maize (Zea mays) mutants mimicking aspects of apomixis, we identified a dominant mutation resulting in the formation of functional unreduced gametes. The mutant shows defects in chromatin condensation during meiosis and subsequent failure to segregate chromosomes. The mutated locus codes for AGO104, a member of the ARGONAUTE family of proteins. AGO104 accumulates specifically in somatic cells surrounding the female meiocyte, suggesting a mobile signal rather than cell-autonomous control. AGO104 is necessary for non-CG methylation of centromeric and knob-repeat DNA. Digital gene expression tag profiling experiments using high-throughput sequencing show that AGO104 influences the transcription of many targets in the ovaries, with a strong effect on centromeric repeats. AGO104 is related to Arabidopsis thaliana AGO9, but while AGO9 acts to repress germ cell fate in somatic tissues, AGO104 acts to repress somatic fate in germ cells. Our findings show that female germ cell development in maize is dependent upon conserved small RNA pathways acting non-cell-autonomously in the ovule. Interfering with this repression leads to apomixis-like phenotypes in maize.

Production of viable gametes without meiosis in maize deficient for an ARGONAUTE protein.

General transcription factor IIB (TFIIB) and TFIIB-related factor (BRF), are conserved RNA polymerase II/III (RNAPII/III) selectivity factors that are involved in polymerase recruitment and transcription initiation in eukaryotes. Recent findings have shown that plants have evolved a third type of B-factor, plant-specific TFIIB-related protein 1 (pBRP1), which seems to be involved in RNAPI transcription. Here, we extend the repertoire of B-factors in plants by reporting the characterization of a novel TFIIB-related protein, plant-specific TFIIB-related protein 2 (pBRP2), which is found to date only in the Brassicacea family. Unlike other B-factors that are ubiquitously expressed, PBRP2 expression is restricted to reproductive organs and seeds as shown by RT-PCR, immunofluorescence labelling and GUS staining experiments. Interestingly, pbrp2 loss-of-function specifically affects the development of the syncytial endosperm, with both parental contributions required for wild-type development. pBRP2, is the first B-factor to exhibit cell-specific expression and regulation in eukaryotes, and might play a role in enforcing bi-parental reproduction in angiosperms.

A plant-specific transcription factor IIB-related protein, pBRP2, is involved in endosperm growth control.

Defining the contributions and interactions of paternal and maternal genomes during embryo development is critical to understand the fundamental processes involved in hybrid vigor, hybrid sterility, and reproductive isolation. To determine the parental contributions and their regulation during Arabidopsis embryogenesis, we combined deep-sequencing-based RNA profiling and genetic analyses. At the 2-4 cell stage there is a strong, genome-wide dominance of maternal transcripts, although transcripts are contributed by both parental genomes. At the globular stage the relative paternal contribution is higher, largely due to a gradual activation of the paternal genome. We identified two antagonistic maternal pathways that control these parental contributions. Paternal alleles are initially downregulated by the chromatin siRNA pathway, linked to DNA and histone methylation, whereas transcriptional activation requires maternal activity of the histone chaperone complex CAF1. Our results define maternal epigenetic pathways controlling the parental contributions in plant embryos, which are distinct from those regulating genomic imprinting.

Maternal epigenetic pathways control parental contributions to Arabidopsis early embryogenesis.

D&eacute;finir les contributions et les interactions entre les g&eacute;nomes paternels et maternels au cours du d&eacute;veloppement de l&#39;embryon est essentiel de comprendre les processus fondamentaux impliqu&eacute;s dans la vigueur hybride, st&eacute;rilit&eacute; des hybrides et isolement reproductif. Pour d&eacute;terminer la contribution parentale et leur r&egrave;glement au cours de l&#39;embryogen&egrave;se de l&#39;Arabidopsis, nous avons combin&eacute; profond-s&eacute;quen&ccedil;age-RNA profilage et g&eacute;n&eacute;tiques analyses bas&eacute;es sur. Au stade 2-4 cellules, il y a une dominance forte, g&eacute;nome entier de transcriptions maternelles, bien que les transcriptions ont &eacute;t&eacute; fournies par les deux g&eacute;nomes parentaux. Au stade globulaire, la contribution relative de paternelle est plus &eacute;lev&eacute;e, en grande partie due &agrave; une activation progressive du g&eacute;nome paternel. Nous avons identifi&eacute; deux voies maternelles antagonistes qui contr&ocirc;lent ces contributions parentales. Les all&egrave;les paternels sont initialement r&eacute;prim&eacute;s par la voie de siRNA de chromatine, li&eacute;e &agrave; la m&eacute;thylation de l&#39;ADN et les histones, tandis que l&#39;activation de la transcription exige une activit&eacute; maternelle de l&#39;histone chaperonner CAF1 complexe. Nos r&eacute;sultats d&eacute;finissent des voies &eacute;pig&eacute;n&eacute;tiques maternelles contr&ocirc;lant la contribution parentale chez les embryons de plantes, qui sont distinctes de celles r&eacute;glementant l&#39;empreinte g&eacute;nomique.

Maternelles voies &eacute;pig&eacute;n&eacute;tiques contr&ocirc;lent parentales contributions au d&eacute;but de l&#39;embryogen&egrave;se Arabidopsis.

Definire i contributi e le interazioni del genoma paterno e materno durante lo sviluppo embrionale &egrave; fondamentale per comprendere i processi fondamentali coinvolti in vigore ibrido, sterilit&agrave; ibrido e isolamento riproduttivo. Per determinare i contributi dei genitori e la loro regolazione durante l&#39;embriogenesi Arabidopsis, siamo combinati basati su deep-sequenziamento RNA analisi genetiche analisi e. Fase la cella 2-4 c&#39;&egrave; una forte, genome-wide dominanza delle trascrizioni materne, anche se le trascrizioni sono inviate da due genomi parentali. Nella fase globulare il relativo contributo paterno &egrave; superiore, in gran parte a causa di un graduale attivazione del genoma paterno. Abbiamo individuato due percorsi materne antagonistiche che controllano questi contributi dei genitori. Alleli paterni sono inizialmente downregolata con il sentiero della cromatina siRNA, legato alla metilazione del DNA e dell&#39;istone, considerando che l&#39;attivazione trascrizionale richiede attivit&agrave; materna dell&#39;istone accompagnatore CAF1 complesso. I nostri risultati definiscono percorsi epigenetici materne controllando i contributi dei genitori in embrioni vegetali, che sono distinti da quelle che regolano imprinting genomico.

Materne percorsi epigenetici controllano parentali contributi all&#39;embriogenesi precoce di Arabidopsis.

Apomictic plants reproduce asexually through seeds by avoiding both meiosis and fertilization. While apomixis is genetically controlled, individual loci contributing to its expression have yet to be identified. Here, we review recent results indicating that RNA-dependent DNA methylation pathways acting during female reproduction are essential for proper reproductive development in plants, and may represent key regulators of the differentiation between apomictic and sexual reproduction.

Epigenetic regulation of reproductive development and the emergence of apomixis in angiosperms.

In plants and animals, embryo development becomes ultimately controlled by zygotic genes, but the timing of zygotic genome activation (ZGA) varies greatly between organisms. We recently showed that the transcriptome of young Arabidopsis embryos is dominated by maternal transcripts with a progressive ZGA under the maternal control of epigenetic pathways. In contrast, another study reported that both parental genomes contribute equally to the transcriptome of young embryos, suggesting that ZGA occurs immediately after fertilization. How to explain such dramatic differences? We propose that the discrepancies between these two studies likely reflect genuine biological differences between the two experiments, paving the road towards exciting discoveries on ZGA mechanisms in plants.

Parental contributions to the transcriptome of early plant embryos.

Chez les plantes et animaux, d&eacute;veloppement de l&#39;embryon devient ultimement contr&ocirc;l&eacute; par des g&egrave;nes zygotiques, mais le moment de l&#39;activation du g&eacute;nome zygotiques (ZGA) varie grandement entre les organismes. Nous avons montr&eacute; r&eacute;cemment que le transcriptome de jeunes embryons d&#39;Arabidopsis est domin&eacute; par des transcriptions maternelles avec un ZGA progressive sous le contr&ocirc;le maternel des voies &eacute;pig&eacute;n&eacute;tiques. En revanche, une autre &eacute;tude indique que les deux g&eacute;nomes parentaux contribuent &eacute;galement au transcriptome de jeunes embryons, ce qui sugg&egrave;re que ZGA se produit imm&eacute;diatement apr&egrave;s la f&eacute;condation. Comment expliquer ces diff&eacute;rences dramatiques ? Nous proposons que les divergences entre ces deux &eacute;tudes susceptibles de refl&egrave;tent v&eacute;ritables diff&eacute;rences biologiques entre les deux exp&eacute;riences, ouvrant la route vers des d&eacute;couvertes int&eacute;ressantes sur les m&eacute;canismes ZGA chez les plantes.

Contributions parentales pour le transcriptome de jeunes embryons de la plante.

In piante e animali, sviluppo dell&#39;embrione diventa infine controllato da geni zygotic, ma i tempi di attivazione del genoma zygotic (ZGA) variano notevolmente tra gli organismi. Abbiamo recentemente mostrato che transcriptome di giovani embrioni di Arabidopsis &egrave; dominato da trascrizioni materne con un progressivo ZGA sotto il controllo materno di percorsi epigenetici. Al contrario, un altro studio ha riferito che entrambi genomi parentali contribuiscono ugualmente transcriptome di giovani embrioni, suggerendo che ZGA si verifica immediatamente dopo la fecondazione. Come spiegare tali differenze drammatiche? Proponiamo che le discrepanze tra questi due studi probabilmente riflettono genuine differenze biologiche tra i due esperimenti, spianando la strada verso emozionanti scoperte sui meccanismi ZGA nelle piante.

Contributi dei genitori transcriptome embrioni vegetali di.

Plants are sessile organisms that must constantly adjust to their environment. In contrast to animals, plant development mainly occurs postembryonically and is characterized by continuous growth and extensive phenotypic plasticity. Chromatin-level regulation of transcriptional patterns plays a central role in the ability of plants to adapt to internal and external cues. Here, we review selected examples of chromatin-based mechanisms involved in the regulation of key aspects of plant development. These illustrate that, in addition to mechanisms conserved between plants and animals, plant-specific innovations lead to particular chromatin dynamics related to their developmental and life strategies.

Epigenetics and development in plants: green light to convergent innovations.

The life cycle of flowering plants is marked by several post-embryonic developmental transitions during which novel cell fates are established. Notably, the reproductive lineages are first formed during flower development. The differentiation of spore mother cells, which are destined for meiosis, marks the somatic-to-reproductive fate transition. Meiosis entails the formation of the haploid multicellular gametophytes, from which the gametes are derived, and during which epigenetic reprogramming takes place. Here we show that in the Arabidopsis female megaspore mother cell (MMC), cell fate transition is accompanied by large-scale chromatin reprogramming that is likely to establish an epigenetic and transcriptional status distinct from that of the surrounding somatic niche. Reprogramming is characterized by chromatin decondensation, reduction in heterochromatin, depletion of linker histones, changes in core histone variants and in histone modification landscapes. From the analysis of mutants in which the gametophyte fate is either expressed ectopically or compromised, we infer that chromatin reprogramming in the MMC is likely to contribute to establishing postmeiotic competence to the development of the pluripotent gametophyte. Thus, as in primordial germ cells of animals, the somatic-to-reproductive cell fate transition in plants entails large-scale epigenetic reprogramming.

Daniel Grimanelli

Institut de Recherche pour le Développement (UMR 232),
Centre National de la Recherche Scientifique (ERL 5300),
Institut de Recherche pour le Développement (UMR 232), Centre National de la Recherche Scientifique (ERL 5300)

Université de Montpellier II

An Efficient Method for Quantitative, Single-cell Analysis of Chromatin Modification and Nuclear Architecture in Whole-mount Ovules in Arabidopsis