Unravelling the core genetic and chromatin-based regulations that control seed development and maturation – SEED-REG

Seeds play a key role in plant dissemination and evolution, as well as in agriculture and food production. Understanding the core mechanisms underpinning seed development and the accumulation of storage compounds therefore constitutes a fundamental goal of plant biology.

The transitions between the successive phases of seed development (i.e embryogenesis, maturation, and germination) and the successful completion of maturation are controlled by the LAFL transcriptional regulators, which are well conserved among angiosperms, namely LEC1, ABI3, FUS3, and LEC2 in Arabidopsis. These regulators can form different protein complexes that control the expression of both structural and regulatory genes involved in various pathways, triggering and maintaining embryo development and maturation, while repressing seed germination. Hence, the LAFL network controls seed development, quality and yield.

Consistent with these key functions, the expression of the LAFL gene is strictly controlled by numerous transcriptional and chromatin-based mechanisms involving, in particular, the PRC complexes. PRC2 is an evolutionary conserved histone H3 lysine 27 methyltransferase (H3K27me3) with a key role in terminating seed development. Moreover, it has been recently hypothesized that the LAFL could themselves modify the chromatin landscape during seed development, acting as “pioneer factors”, by recruiting different chromatin regulators that remain to be characterized.

Despite their critical role, we still ignore how the LAFL and chromatin modifiers interact to control both, phase transitions and seed maturation. We believe that the chromatin-based regulations of LAFL expression, the pleiotropic effects of LAFL mutations, and the difficulty of accessing specific tissues inside the seed (i.e. the embryo surrounded by the endosperm and the testa) have prevented deciphering the mechanisms involved and hidden the fact that the LAFL may themselves impinge on chromatin state. Another hurdle resides in the small size of the seed and the tricky access to the embryonic tissues within seeds.

To discover possible yet unknown players and elucidate the molecular mechanisms involved, it is now crucial to apply novel approaches to monitor chromatin and transcriptome dynamics within the seed in a tissue-specific manner. Moreover, to unravel the epistatic relationships between the LAFL and chromatin regulators, we need to develop new inducible alleles allowing to precisely activate or repress these regulators or/and to uncouple LAFL expression from chromatin regulations.

Therefore, the ambition of the project is to develop original approaches and tools to identify novel regulators and elucidate how the LAFL interact with chromatin-based mechanisms to control proper seed development and maturation.

The short-term outputs of this project will be both scientific and technical. We will indeed need to use cutting-edge techniques recently adapted in our labs, generate original inducible, and/or tissue-specific alleles, and will edit the epigenome of the LAFL using a new CRISPR/dCas9 approach. Using Arabidopsis will be essential and an asset to perform all these molecular and genetic analyses in the frame of the project. The main scientific outcome of this project will consist in knowledge on the genetic and molecular mechanisms that control seed development and maturation.

Beyond seeds, the project will contribute to decipher fundamental mechanisms of phase transitions during plant development and will exemplify if and/or to which extent chromatin modifications and transcriptional regulation are impinging on each other. Last, because the LAFL and chromatin regulators are conserved among angiosperms, including crop species, this project may deeply impact agriculture on the long term. In conclusion, this project may therefore provide major scientific, societal and environmental benefits