Nanopore RNA direct sequencing identifies that mA 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 N-methyladenosine (mA) 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 mA 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 mA modification stabilizes their mRNAs and improves translation efficiency. These data identify that mA modification through MdVIR1 and MdVIR2 methyltransferases is essential for sorbitol-controlled resistance to A. alternata.