The secreted GH43 protein VpGHa1 functions as an effector to suppress plant immunity and contributes to stress adaptation in Valsa pyri

Introduction While the pear canker pathogen Valsa pyri typically employs cell wall-degrading enzymes to breach host barriers, the functions of its glycoside hydrolase family 43 (GH43) proteins remain largely unexplored. Methods Here, using genetic manipulation, secretion assays, transient-expression assays, and transcriptomic analysis, we investigated whether the GH43 protein VpGHa1 contributes to fungal virulence, stress adaptation, and suppression of host immunity. Results VpGHa1 contains a predicted signal peptide and a GH43_AnAbnA-like domain. VpGHa1 expression was strongly induced during the early stages of infection, and the protein was confirmed to be secreted. Sequence analysis predicted an endo-1,5-α-L-arabinofuranosidase-related function, and recombinant VpGHa1 showed positive anti-arabinase immunoreactivity in an antibody-based ELISA. Deletion of VpGHa1 reduced lesion size on pear twigs by 33.8%, whereas genetic complementation significantly restored the reduced-virulence phenotype and overexpression enhanced pathogenicity without affecting vegetative growth. The ΔVpGHa1 mutant showed increased tolerance to KCl but greater sensitivity to NaCl and H₂O₂, indicating that VpGHa1 contributes to ionic and oxidative stress adaptation. Furthermore, transient expression of VpGHa1 in Nicotiana benthamiana suppressed BAX- and INF1-induced cell death, promoted colonization by Sclerotinia sclerotiorum, and enhanced lesion formation after V. pyri challenge in apple leaves; this was accompanied by downregulation of apple defense-related genes. Transcriptomic analysis identified 115 DEGs between the WT and ΔVpGHa1 mutant and revealed enrichment of carbohydrate-related, extracellular/cell-surface-associated, and metabolic processes, suggesting broad transcriptional effects associated with cell-surface and metabolic adaptation. Discussion Together, these findings identify VpGHa1 as a multifunctional secreted GH43 virulence factor linking pathogenicity, stress adaptation, and host immune suppression, whereas its predicted arabinan-related enzymatic activity remains to be experimentally validated.