Arabidopsis m 6 A demethylase activity modulates viral infection of a plant virus and the m 6 A abundance in its genomic RNAs.

N6 -methyladenosine (m6 A) is an internal, reversible nucleotide modification that constitutes an important regulatory mechanism in RNA biology. Unlike mammals and yeast, no component of the m6 A cellular machinery has been described in plants at present. m6 A has been identified in the genomic RNAs of diverse mammalian viruses and, additionally, viral infection was found to be modulated by the abundance of m6 A in viral RNAs. Here we show that the Arabidopsis thaliana protein atALKBH9B (At2g17970) is a demethylase that removes m6 A 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 m6 A demethylase activity could be linked to mRNA silencing and/or mRNA decay processes. Moreover, we identified the presence of m6 A 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 m6 A 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, m6 A modification may represent a plant regulatory strategy to control cytoplasmic-replicating RNA viruses.