The RNA binding protein EHD6 recruits the m6A reader YTH07 and sequesters OsCOL4 mRNA into phase-separated ribonucleoprotein condensates to promote rice flowering

Abstract

N6-methyladenosine (m6A) is one of the most abundant modifications in eukaryotic mRNA, but the comprehensive biological functionality continues to be a subject for exploration. In this study, we identified and characterized a new flowering-promoting gene EARLY HEADING DATE6 (EHD6) in rice. EHD6 encodes an RNA recognition motif (RRM)-containing RNA binding protein that is localized in the non-membranous cytoplasm ribonucleoprotein (RNP) granules and can bind both m6A-modified RNA and unmodified RNA indiscriminately. We found that EHD6 can physically interact with YTH07, a YTH (YT521-B homology) domain containing m6A reader, and their interaction enhances the binding of m6A-modified RNA and triggers relocation of a part of YTH07 from the cytoplasm into RNP granules through phase-separated condensation. Within these condensates, the mRNA of a rice flowering repressor, CONSTANS-like 4 (OsCOL4), becomes sequestered, leading to a reduction in its protein abundance and thus affect flowering through the Early heading date 1 pathway. Our results not only shed new light on the molecular mechanism of efficient m6A recognition by the collaboration between the RNA binding protein and YTH family m6A reader, but also uncovers a potential m6A mediated translation regulation through phase-separated ribonucleoprotein condensation in rice.