PME10 Is a Pectin Methylesterase Driving PME Activity and Immunity Against Botrytis cinerea in Grapevine ( Vitis vinifera L.)

Botrytis cinerea (Bc) is a major pathogen of cultivated grapevine (Vitis vinifera L.), with cell wall (CW) remodelling playing a critical role in fungal colonisation. CW-modifying enzymes, particularly pectin methylesterases (PMEs), produced by both host and pathogen, influence CW integrity and the outcome of infection. To explore the role of CW composition and remodelling in grapevine's response to Bc, we inoculated three genotypes with varying susceptibility at full flowering. Biochemical analysis of flowers and ripe berry skins revealed that the tolerant genotype exhibited significantly higher PME activity postinfection compared with the susceptible ones. Unbiased transcriptome analysis of infected flower tissues showed a more intense transcriptional response in the susceptible genotype, suggesting an ultimately ineffective attempt to restrict fungus spread. Expression profiling of 62 PME genes in this data set and public Bc-infected berry transcriptomes identified PME10 as the most strongly induced gene upon infection. PME10 knockout mutants displayed reduced PME activity and heightened susceptibility, while overexpression lines showed enhanced PME activity and reduced disease symptoms. Gene co-expression network analysis highlighted WRKY03, a defence-related transcription factor, as a putative regulator of PME10. DAP-seq, DAP-qPCR and dual luciferase assays confirmed direct binding and activation of the PME10 promoter by WRKY03. Altogether, this study demonstrates that PME10 is a functional PME contributing to grapevine immunity against B. cinerea, establishing it as a key component of the grapevine defence machinery against fungal pathogens.