Extended Data Fig. 10: Analysis of the TaRVR-A1/B1/D1 proteins and chromatin-based regulation of TaVRN1 expression.
a, Domain architectures of AtAIPP3, BdRVR1 and TaRVR-A1/B1/D1 (from KN9204). b, Protein sequence alignment of AtAIPP3 and TaRVR-A1/B1/D1. Black- and grey-shaded residues indicate identical and similar residues, respectively. BAH domains are underlined with a blue line. Red stars denote the conserved key residues for H3K27me3 recognition. c, Structure superposition of BAH domains of AtAIPP3 (magenta) and TaRVR-A1/B1/D1 (cyan) using the Pymol program (https://pymol.org/2/). The BAH domain structure of TaRVR1 is modeled using the Phyre2 program (http://www.sbg.bio.ic.ac.uk/phyre2/). d, A working model for switching TaVRN1 chromatin state in response to prolonged cold and development state (embryogenesis) in the life cycle of winter bread wheat. Prior to cold, PRC2 deposits the repressive H3K27me3 marks on TaVRN1 chromatin. TaRVR1, likely in a complex with TaAIPP2 and TaCPL2 (Pol II dephosphorylation), functions together with Polycomb group factors to read and maintain the Polycomb-repressed state at TaVRN1, and thus to repress its repression. This, together with TaVRN2 expression in vascular bundles, confers winter-annual growth habit in wheat. Prolonged cold exposure in winter led to a strong reduction in H3K27me3 at TaVRN1 and consequent disruption of TaRVR1 function, and TaVRN1 chromatin is highly enriched with both H3K4me3 and H3K36me3. Hence, prolonged cold leads to a switching of the Polycomb-repressed state to a highly active state. Moreover, cold exposure may induce TaVRN1 expression through cold-responsive transcriptional regulators (TFs). Conceivably, these TFs may function in concert with TaRVR1 and chromatin modifiers to mediate cold induction of TaVRN1 expression. Upon embryonic resetting of TaVRN1 expression, TaVRN1 chromatin is switched back to Polycomb-repressed state. Note that the conserved COMPASS-like H3K4 methyltransferase complex and the H3K36 methyltransferase EFS are expected to deposit H3K4me3 and H3K36me3 at TaVRN1, respectively. S5(P) for Pol II phosphorylated on Serine 5.
