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

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 Md MDS1'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.