The Malectin‐like kinase gene <scp> <i>Md</i> MDS1 </scp> negatively regulates the resistance of <i>Pyrus betulifolia</i> to Valsa canker by promoting the expression of <scp> <i>Pbe</i> PME1 </scp>

Valsa canker, caused by fungal pathogens in Valsa species, is a fungal disease of apple and pear growing in China and even in Asia. Malectin-like kinases play crucial roles in plant recognition of the pathogen-induced signals and subsequent activation of partially host immune responses. However, the role of MEDOS1 (MDS1), a Malectin-like kinase, in plant immunity has not yet been extensively explored. Here, we found that the expression of the Malus domestica MDS (MdMDS1) gene, a homologous gene of the Catharanthus roseus Receptor-Like Kinase 1-like (CrRLK1L) family member MDS1 in Arabidopsis, could be inhibited by Valsa canker signals. Over-expression of MdMDS1 decreased Valsa canker resistance of apple and pear fruits, as well as 'Duli-G03' (Pyrus betulifolia) suspension cells. In response to Valsa pyri (Vp) signals in suspension cells, the up-regulation of MdMDS1 caused the inhibition of defense-related genes but activated the expression of cell wall-related genes. Among these, the pectin methylesterase gene PbePME1 was robustly induced. Further analysis confirmed that PbePME1, a negative regulator of Valsa canker resistance, was indispensable for MdMDS1's function. Our results enriched the recognization of the functions of CrRLK1L genes in host resistance against necrotrophics. We also provided a theoretical reference for the resistance breeding and comprehensive control of Valsa canker in both apples and pears.