Nanopore RNA direct sequencing identifies that m6A modification is essential for sorbitol-controlled resistance to Alternaria alternata in apple

Sorbitol, a main photosynthate and transport carbohydrate in all tree fruit species in Rosaceae, acts as a signal controlling resistance against Alternaria (A.) alternata in apple by altering the expression of the MdNLR16 resistance gene via the MdWRKY79 transcription factor. However, it is not known if N⁶-methyladenosine (m⁶A) methylation of the mRNAs of these genes participates in the process. Here, we found that decreased sorbitol synthesis in apple leaves leads to a transcriptome-wide reduction in the m⁶A modification, with fewer transcripts containing two or more methylation sites. We identified two methyltransferases, MdVIR1 and MdVIR2, that respond to sorbitol and A. alternata inoculation and positively control resistance to A. alternata. MdVIR1 and MdVIR2 act on MdWRKY79 and MdNLR16 mRNAs, and the resulting m⁶A modification stabilizes their mRNAs and improves translation efficiency. These data identify that m⁶A modification through MdVIR1 and MdVIR2 methyltransferases is essential for sorbitol-controlled resistance to A. alternata.