Nuclear body structures in transcriptional regulation of seed size control and/or plant defence pathways.

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Ensuring food security in the future will be of increasing importance with the rising world population and negative impact from climate change on arable land. Rice feeds half the world’s population and there has been tremendous efforts to increase yield through breeding. Many lines of genetic evidence point to a MAPK (mitogen-activated protein kinase) cascade that promote larger grain size development but the downstream molecular mechanism is still unknown. We identified IKU1 (a component of a complex known to transcriptionally regulate seed/endosperm development in Arabidopsis) to be a MAPK phospho-substrate. Therefore, in collaboration with colleagues in India, we propose to test the hypothesis if a candidate rice IKU-like protein might be the missing link to grain size control downstream of the MAPK cascade. In parallel, we will utilize the Arabidopsis system for functional elucidation of the molecular mechanism underpinning IKU1 functions. In agreement to predicted intrinsic disorder and prion domain-like (PrD-like) regions, we observed IKU1 localization to nuclear foci when fused to a GFP-tag. Preliminary results suggest a MAPK-mediated effect on foci dynamics. Such foci presumably represent phase partitioning of proteins into biomolecular condensates or sometimes referred to as “membrane-less organelles”, which is an emerging field of research. Biomolecular condensates are thought to facilitate high local protein concentrations to drive certain biochemical processes. In this application, we propose to study how proteoforms (post-translational modifications, splice variants, natural variations in PrD-like promoting amino acids) in IKU1 affect the condensate dynamics and/or its interaction with protein partners – with the aim to link these data to seed size control or eventual crosstalk to plant defence regulation.