Polycomb repressive complex 2 (PRC2) is a key regulator of epigenetic states catalyzing histone H3 lysine 27 trimethylation (H3K27me3), a repressive chromatin mark. PRC2 composition is conserved from humans to plants, but the function of PRC2 during the early stage of plant life is unclear beyond the fact that it is required for the development of endosperm, a nutritive tissue that supports embryo growth. Circumventing the requirement of PRC2 in endosperm allowed us to generate viable homozygous null mutants for FERTILIZATION INDEPENDENT ENDOSPERM (FIE), which is the single Arabidopsis homolog of Extra Sex Combs, an indispensable component of Drosophila and mammalian PRC2. Here we show that H3K27me3 deposition is abolished genome-wide in fie mutants demonstrating the essential function of PRC2 in placing this mark in plants as in animals. In contrast to animals, we find that PRC2 function is not required for initial body plan formation in Arabidopsis. Rather, our results show that fie mutant seeds exhibit enhanced dormancy and germination defects, indicating a deficiency in terminating the embryonic phase. After germination, fie mutant seedlings switch to generative development that is not sustained, giving rise to neoplastic, callus-like structures. Further genome-wide studies showed that only a fraction of PRC2 targets are transcriptionally activated in fie seedlings and that this activation is accompanied in only a few cases with deposition of H3K4me3, a mark associated with gene activity and considered to act antagonistically to H3K27me3. Up-regulated PRC2 target genes were found to act at different hierarchical levels from transcriptional master regulators to a wide range of downstream targets. Collectively, our findings demonstrate that PRC2-mediated regulation represents a robust system controlling developmental phase transitions, not only from vegetative phase to flowering but also especially from embryonic phase to the seedling stage.
Double fertilization of the egg cell and the central cell by one sperm cell each produces the diploid embryo and the typically triploid endosperm and is one of the defining characteristics of flowering plants (angiosperms). Endosperm and embryo develop in parallel to form the mature seed, but little is known about the coordination between these two organisms. We characterized a mutation of the Arabidopsis thaliana Cdc2 homolog CDC2A (also called CDKA;1), which has a paternal effect. In cdc2a mutant pollen, only one sperm cell, instead of two, is produced. Mutant pollen is viable but can fertilize only one cell in the embryo sac, allowing for a genetic dissection of the double fertilization process. We observed exclusive fertilization of the egg cell by cdc2a sperm cells. Moreover, we found that unfertilized endosperm developed, suggesting that a previously unrecognized positive signal from the fertilization of the egg cell initiates proliferation of the central cell.Plants have a complex life cycle involving the alternation of a diploid sporophytic and a haploid gametophytic phase. In flowering plants, the female spore (megaspore), generated from the sporophyte, typically develops through a series of syncytial nuclear divisions followed by 'cellularization' into a seven-celled female gametophyte (embryo sac) comprising three antipodals, two synergids, a binucleated central cell and the egg cell 1 . The male spore (microspore) undergoes a defined cell division program resulting in a male gametophyte (pollen grain) comprising a vegetative cell that encloses two sperm cells 2 .Cell divisions in plants, as in other higher eukaryotes, are controlled by a class of serine-threonine kinases called cyclin-dependent kinases (CDKs). Some of the central CDKs in plants are A-type CDK proteins. A. thaliana contains only one A-type CDK, called CDC2A (or CDKA;1), which can rescue the fission yeast cdc2 mutant [3][4][5] . Previous studies with dominant negative variants showed that CDC2A activity is required for entering both mitosis and the DNA synthesis-phase in A. thaliana, maize and tobacco [6][7][8] .
Based on their evolutionary origin, MADS box transcription factor genes have been divided into two classes, namely, type I and II. The plant-specific type II MIKC MADS box genes have been most intensively studied and shown to be key regulators of developmental processes, such as meristem identity, flowering time, and fruit and seed development. By contrast, very little is known about type I MADS domain transcription factors, and they have not attracted interest for a long time. A number of recent studies have now indicated a key regulatory role for type I MADS box factors in plant reproduction, in particular in specifying female gametophyte, embryo, and endosperm development. These analyses have also suggested that type I MADS box factors are decisive for setting reproductive boundaries between species. MADS DOMAIN ENCODING GENESMADS box genes are of ancient origin and are found in animals, fungi, and plants. All identified MADS box genes encode a highly conserved N-terminal DNA binding domain 55 to 60 amino acids in length named the MADS domain ( Figure 1; Trö bner et al., 1992). Homology searches in the nonredundant microbial database using a Hidden Markov Model for seed alignment of the MADS domain suggested that the MADS domain originates from the DNA binding subunit A of topoisomerases IIA subunit A (Gramzow et al., 2010).The acronym MADS ) is derived from the initials of MINICHROMOSOME MAINTENANCE1 (MCM1, Saccharomyces cerevisiae; Passmore et al., 1988), AGAMOUS (Arabidopsis thaliana; Yanofsky et al., 1990), DEFI-CIENS (Antirrhinum majus; Sommer et al., 1990), and SERUM RESPONSE FACTOR (SRF, Homo sapiens; Norman et al., 1988). These members of the MADS box gene family play important biological roles; for example, the human SRF coordinates the transcription of the proto-oncogene c-fos (Masutani et al., 1997;Mo et al., 2001), while MCM1 is central to the transcriptional control of cell type-specific genes and the pheromone response in the yeast S. cerevisiae (Shore and Sharrocks, 1995;Mead et al., 2002).Plant MADS box genes were first identified as regulators of floral organ identity and have since been reported to control additional developmental processes, such as the determination of meristem identity of vegetative, inflorescence, and floral meristems, root growth, ovule and female gametophyte development, flowering time, fruit ripening, and dehiscence (Zhang and Forde, 1998;Ng and Yanofsky, 2001;Giovannoni, 2004;Whipple et al., 2004;Liu et al., 2009). Studies using several model species, including Arabidopsis, A. majus, Petunia hybrida, Zea mays, and Oryza sativa, have revealed that many of these functions are conserved among angiosperms (Schwarz-Sommer et al., 2003;Vandenbussche et al., 2003;Kater et al., 2006). ARABIDOPSIS MADS BOX TYPE I AND TYPE II: AN EVOLUTIONARY OVERVIEWBased on sequence conservation in the MADS domain, these transcription factors can be grouped into two main lineages, named type I (SRF-like) and type II (MEF2-like; Alvarez-Buylla et al., 2000). In animals, type I genes are involv...
Based on the biological species concept, two species are considered distinct if reproductive barriers prevent gene flow between them. In Central Europe, the diploid species Arabidopsis lyrata and Arabidopsis arenosa are genetically isolated, thus fitting this concept as "good species." Nonetheless, interspecific gene flow involving their tetraploid forms has been described. The reasons for this ploidy-dependent reproductive isolation remain unknown. Here, we show that hybridization between diploid A. lyrata and A. arenosa causes mainly inviable seed formation, revealing a strong postzygotic reproductive barrier separating these two species. Although viability of hybrid seeds was impaired in both directions of hybridization, the cause for seed arrest differed. Hybridization of A. lyrata seed parents with A. arenosa pollen donors resulted in failure of endosperm cellularization, whereas the endosperm of reciprocal hybrids cellularized precociously. Endosperm cellularization failure in both hybridization directions is likely causal for the embryo arrest. Importantly, natural tetraploid A. lyrata was able to form viable hybrid seeds with diploid and tetraploid A. arenosa, associated with the reestablishment of normal endosperm cellularization. Conversely, the defects of hybrid seeds between tetraploid A. arenosa and diploid A. lyrata were aggravated. According to these results, we hypothesize that a tetraploidization event in A. lyrata allowed the production of viable hybrid seeds with A. arenosa, enabling gene flow between the two species.interspecies hybrid seed failure | Arabidopsis | reproductive isolation | endosperm cellularization | EBN
BackgroundMADS-domain transcription factors play important roles during plant development. The Arabidopsis MADS-box gene SHORT VEGETATIVE PHASE (SVP) is a key regulator of two developmental phases. It functions as a repressor of the floral transition during the vegetative phase and later it contributes to the specification of floral meristems. How these distinct activities are conferred by a single transcription factor is unclear, but interactions with other MADS domain proteins which specify binding to different genomic regions is likely one mechanism.ResultsTo compare the genome-wide DNA binding profile of SVP during vegetative and reproductive development we performed ChIP-seq analyses. These ChIP-seq data were combined with tiling array expression analysis, induction experiments and qRT-PCR to identify biologically relevant binding sites. In addition, we compared genome-wide target genes of SVP with those published for the MADS domain transcription factors FLC and AP1, which interact with SVP during the vegetative and reproductive phases, respectively.ConclusionsOur analyses resulted in the identification of pathways that are regulated by SVP including those controlling meristem development during vegetative growth and flower development whereas floral transition pathways and hormonal signaling were regulated predominantly during the vegetative phase. Thus, SVP regulates many developmental pathways, some of which are common to both of its developmental roles whereas others are specific to only one of them.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.