N 6-methyladenosine (m 6A) modification has been found to constitute an important regulatory mechanism in RNA biology. Unlike mammals and yeast, no component of the m 6A cellular machinery has been described in plants at present. Although the influence of the m6A cellular machinery has been suspected to occur in the plant virus cycle, it has never been proved. Here we have identified a plant protein with m 6A demethylase activity (atALKBH9B) and demonstrate that this protein removes m 6A modification from RNA in vitro. Remarkably, we found that m 6A abundance on the viral genome of alfalfa mosaic virus is influenced by atALKBH9B activity and regulates viral infection. This study extends the vast repertoire that plants exploit to control cytoplasmic-replicating RNA viruses.
N 6-methyladenosine (m 6A) is an internal, reversible nucleotide modification that constitutes an important regulatory mechanism in RNA biology. Unlike mammals and yeast, no component of the m 6A cellular machinery has been described in plants at present. m 6A has been identified in the genomic RNAs of diverse mammalian viruses and, additionally, viral infection was found to be modulated by the abundance of m 6A in viral RNAs. Here we show that the Arabidopsis thaliana protein atALKBH9B (At2g17970) is a demethylase that removes m 6A from single-stranded RNA molecules in vitro. atALKBH9B accumulates in cytoplasmic granules, which colocalize with siRNA bodies and associate with P bodies, suggesting that atALKBH9B m 6A demethylase activity could be linked to mRNA silencing and/or mRNA decay processes. Moreover, we identified the presence of m 6A in the genomes of two members of the Bromoviridae family, alfalfa mosaic virus (AMV) and cucumber mosaic virus (CMV). The demethylation activity of atALKBH9B affected the infectivity of AMV but not of CMV, correlating with the ability of atALKBH9B to interact (or not) with their coat proteins. Suppression of atALKBH9B increased the relative abundance of m 6A in the AMV genome, impairing the systemic invasion of the plant, while not having any effect on CMV infection. Our findings suggest that, as recently found in animal viruses, m 6A modification may represent a plant regulatory strategy to control cytoplasmic-replicating RNA viruses.