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

The yeast halotolerance gene HAL2 encodes a nucleotidase that dephosphorylates 3-phosphoadenosine 5-phosphate (PAP) and 3-phosphoadenosine 5-phosphosulfate (PAPS), intermediates of the sulfate assimilation pathway. This nucleotidase is inhibited by Na ؉ and Li