ALBA-YTHDF-m6A axis in plants

N6-methyladenosine (m6A) in mRNA exerts many of its effects in regulation of eukaryotic gene expression by recruitment of cytoplasmic RNA-binding proteins containing a YT521-B homology (YTH) domain specialized for m6A-interaction. In plants, these so-called YTHDF proteins promote growth by stimulation of cell division in organ primordia by ill-defined mechanisms. Here, we show that the widely conserved family of mRNA-binding ALBA proteins interact with YTHDF proteins in the plant Arabidopsis thaliana. mRNA targets of ALBA proteins and the YTHDF proteins ECT2 and ECT3 overlap substantially, and nearly all ALBA4 targets with 3'-UTR binding sites are also m6A-ECT2/ECT3 targets. ALBA4 binding sites are located immediately upstream of m6A sites and correspond to the pyrimidine-rich elements previously suggested to be important for ECT2 binding. Accordingly, an ECT2 mutant protein defective in ALBA association binds less RNA in vivo compared to wild type, and many ECT2 targets exhibit less association with ECT2 in vivo in the absence of four of the six arabidopsis ALBA proteins. We propose that ALBA proteins facilitate assembly and function of m6A-YTHDF-containing mRNPs, thereby promoting plant growth.