CHARACTERIZATION OF A METHYLTRANSFERASE, FIONA1, IN FLOWERING TIME CONTROL IN ARABIDOPSIS

Abstract

N6-methyladenosine (m6A) mRNA modification represents the most widespread form of internal modifications in eukaryotic mRNAs. m6A deposition requires the methyltransferases mRNA adenosine methylase (MTA) and MTB in Arabidopsis thaliana, yet whether it also requires other methyltransferase(s) remains unknown. Here, we show that FIONA1 (FIO1), an METTL16 ortholog, acts as a hitherto unknown m6A methyltransferase, which underlies the regulation of flowering time in Arabidopsis. Mutants of FIO1 show an early-flowering phenotype and a decrease in global m6A mRNA methylation level. Nanopore direct RNA sequencing reveals that FIO1 is required for establishing appropriate levels of m6A preferentially in the coding sequences of a subset of protein-coding transcripts, including key regulators in circadian rhythm and flowering time control. Our results demonstrate FIO1 as an m6A methyltransferase that is responsible for the m6A methylation mainly in the coding sequences, extending of our current understanding of how plants establish their m6A landscapes.