SEED-DREAM Lab info

Polycomb Repressive Complex 2 (PRC2)-mediated trimethylation of histone H3 on lysine 27 (H3K27me3) and methylation of histone 3 on lysine 9 (H3K9me) are two repressive epigenetic modifications that are typically localized in distinct regions of the genome. For reasons unknown, however, they co-occur in some organisms and special tissue types. In this study, we show that maternal alleles marked by H3K27me3 in the Arabidopsis endosperm were targeted by the H3K27me3 demethylase REF6 and became activated during germination. In contrast, maternal alleles marked by H3K27me3, H3K9me2, and CHG methylation (CHGm) are likely to be protected from REF6 targeting and remained silenced. Our study unveils that combinations of different repressive epigenetic modifications time a key adaptive trait by modulating access of REF6.

Axel Kahn, médecin, généticien et essayiste, est mort à 76 ans des suites d’un cancer, a annoncé mardi 6 juillet la Ligue contre le cancer, dont il était président depuis juin 2019. Il avait lui-même pris l’initiative d’en annoncer l’issue fatale, le 11 mai, dans un communiqué. Il avait ensuite accordé une série d’entretiens, dans lesquels il faisait part de sa sérénité face à la mort, témoignant de l’expérience « saisissante » que l’on vit quand on la sait toute proche : « La joie de tout instant de beauté est décuplée par l’hypothèse que l’on pourrait n’en plus connaître de pareille. Sensation inouïe, bonheur immense », écrivait-il ainsi le 14 mai sur son fil Twitter, en regard de fleurs et d’un arc-en-ciel.

LEAFY COTYLEDON1 (LEC1), a NUCLEAR FACTOR‐Y (NF‐Y) family member, plays a critical role in Arabidopsis embryogenesis and seed development. Previous studies have shown that OsNF‐YB9 and OsNF‐YB7 of rice are homologous to Arabidopsis LEC1. However, the functions of LEC1‐like genes in rice remain unclear. Here we report that OsNF‐YB9 and OsNF‐YB7 display sub‐functionalization in rice. We demonstrate that OsNF‐YB7 is expressed mainly in embryo, whereas OsNF‐YB9 is preferentially expressed in the developing endosperm. Heterologous expression of either OsNF‐YB9 or OsNF‐YB7 in Arabidopsis lec1‐1 was able to complement the lec1‐1 defects. We failed to generate osnf‐yb7 homozygous mutants due to lethality caused by OsNF‐YB7defects. Loss of OsNF‐YB9 function caused abnormal seed development: seeds were longer, narrower, and thinner and exhibited a higher chalkiness ratio. Furthermore, the expression of genes related to starch synthesis was deregulated in osnf‐yb9. OsNF‐YB9 could interact with SPK, a sucrose synthase protein kinase that predominantly expressed in rice endosperm. Knockout of SPK resulted in chalky seeds similar to that observed in the osnf‐yb9 mutants. Ectopic expression of OsNF‐YB9 in both rice and Arabidopsis resulted in unhealthy plants with small seeds. Taken together, these results suggest a critical role for OsNF‐YB9 in rice seed development.

Grain filling and grain development are essential biological processes in the plant’s life cycle, eventually contributing to the final seed yield and quality in all cereal crops. Studies of how the different wheat (Triticum aestivum L.) grain components contribute to the overall development of the seed are very scarce. We performed a proteomics and metabolomics analysis in four different developing components of the wheat grain (seed coat, embryo, endosperm, and cavity fluid) to characterize molecular processes during early and late grain development. In-gel shotgun proteomics analysis at 12, 15, 20, and 26 days after anthesis (DAA) revealed 15 484 identified and quantified proteins, out of which 410 differentially expressed proteins were identified in the seed coat, 815 in the embryo, 372 in the endosperm, and 492 in the cavity fluid. The abundance of selected protein candidates revealed spatially and temporally resolved protein functions associated with development and grain filling. Multiple wheat protein isoforms involved in starch synthesis such as sucrose synthases, starch phosphorylase, granule-bound and soluble starch synthase, pyruvate phosphate dikinase, 14-3-3 proteins as well as sugar precursors undergo a major tissue-dependent change in abundance during wheat grain development suggesting an intimate interplay of starch biosynthesis control. Different isoforms of the protein disulfide isomerase family as well as glutamine levels, both involved in the glutenin macropolymer pattern, showed distinct spatial and temporal abundance, revealing their specific role as indicators of wheat gluten quality. Proteins binned into the functional category of cell growth/division and protein synthesis/degradation were more abundant in the early stages (12 and 15 DAA). At the metabolome level all tissues and especially the cavity fluid showed highly distinct metabolite profiles. The tissue-specific data are integrated with biochemical networks to generate a comprehensive map of molecular processes during grain filling and developmental processes.

Key takeaways

Polycomb repressive complex (PRC)-mediated gene silencing is vital for cell identity and development in both the plant and the animal kingdoms. It also modulates responses to stress. Two major protein complexes, PRC1 and PRC2, execute conserved nuclear functions in metazoans and plants through covalent modification of histones and by compacting chromatin. While a general requirement for Polycomb complexes in mitotically heritable gene repression in the context of chromatin is well established, recent studies have brought new insights into the regulation of Polycomb complex activity and recruitment.

MEDEA, a Polycomb Repressive Complex 2 (PRC2) subunit, is required in embryo and endosperm

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MEDEA links cell proliferation and differentiation during embryonic pattern formation

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The PRC2 protein MEDEA directly regulates core cell-cycle components, i.e., cyclin CYCD1;1

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Body plan and cell proliferation are epigenetically regulated in both animals and plants

Proanthocyanidins (PAs) are plant natural products important for agriculture and human health. They are polymers of flavan-3-ol subunits, commonly (−)-epicatechin and/or (+)-catechin, but the source of the in planta extension unit that comprises the bulk of the polymer remains unclear, as does how PA composition is determined in different plant species. Anthocyanidin reductase (ANR) can generate 2,3-cis-epicatechin as a PA starter unit from cyanidin, which itself arises from 2,3-trans-leucocyanidin, but ANR proteins from different species produce mixtures of flavan-3-ols with different stereochemistries in vitro. Genetic and biochemical analyses here show that ANR has dual activity and is involved not only in the production of (−)-epicatechin starter units but also in the formation of 2,3-cis-leucocyanidin to serve as (−)-epicatechin extension units. Differences in the product specificities of ANRs account for the presence/absence of PA polymerization and the compositions of PAs across plant species.

Summary

Interactions between land plants and other organisms such as pathogens, pollinators, or symbionts usually involve a variety of specialized effectors participating in complex cross-talks between organisms. Fatty acids and their lipid derivatives play important roles in these biological interactions. While the transcriptional regulation of genes encoding acyl–acyl carrier protein (ACP) desaturases appears to be largely responsive to biotic stress, the different monounsaturated fatty acids produced by these enzymes were shown to take active part in plant biotic interactions and were assigned with specific functions intrinsically linked to the position of the carbon–carbon double bond within their acyl chain. For example, oleic acid, an omega-9 monounsaturated fatty acid produced by ∆9-stearoyl–ACP desaturases, participates in signal transduction pathways affecting plant immunity against pathogen infection. Myristoleic acid, an omega-5 monounsaturated fatty acid produced by ∆9-myristoyl–ACP desaturases, serves as a precursor for the biosynthesis of omega-5 anacardic acids that are active biocides against pests. Finally, different types of monounsaturated fatty acids synthesized in the labellum of orchids are used for the production of a variety of alkenes participating in the chemistry of sexual deception, hence favoring plant pollination by hymenopterans.