The m6A writer FIONA1 methylates the 3’UTR of FLC and controls flowering in Arabidopsis

ABSTRACT Adenosine bases of RNA can be transiently modified by the deposition of a methyl-group to form N 6 -methyladenosine (m 6 A). This adenosine-methylation is an ancient process and the enzymes involved are evolutionary highly conserved. A genetic screen designed to identified suppressors of late flowering transgenic Arabidopsis plants overexpressing the miP1a microProtein yielded a new allele of the FIONA1 (FIO1) m 6 A-methyltransferase. To characterize the early flowering phenotype of fio1 mutant plants we employed an integrative approach of mRNA-seq, Nanopore direct RNA-sequencing and meRIP-seq to identify differentially expressed transcripts as well as differentially methylated mRNAs. We provide evidence that FIO1 is the elusive methylase responsible for the 3’-end methylation of the FLOWERING LOCUS C ( FLC ) transcript. Furthermore, our genetic and biochemical data suggest that 3’-methylation stabilizes FLC mRNAs and non-methylated FLC is a target for rapid degradation.