VmPma1 contributes to virulence via regulation of the acidification process during host infection in Valsa mali

Valsa mali is a destructive phytopathogenic fungus that mainly infects apple and pear trees. Infection with V. mali results in host tissue acidification via the generation of citric acid, which promote invasion. Here, two plasma membrane H+-ATPases, VmPma1 and VmPma2, were identified in V. mali. The VmPma1 deletion mutant (Delta VmPma1) displayed higher intracellular acid accumulation and a lower growth rate compared to the wild type. In contrast, the VmPma2 deletion mutant (Delta VmPma2) showed no obvious phenotypic differences. Meanwhile, loss of VmPma1, but not VmPma2, in V. mali led to a significant decrease in growth under acidic or alkaline conditions compared with WT. More importantly, Delta VmPma1 showed a greater reduction in ATPase hydrolase activity and acidification of the external environment, more sensitivity to abiotic stress, and weaker pathoge-nicity than Delta VmPma2. This evidence indicates that VmPma1 is the main gene of the two plasma membrane H+- ATPases. Transcriptomic analysis indicated that many metabolic processes regulated by VmPma1 are strictly pH-regulated. Besides, we identified two genes (named VmAgn1p and Vmap1) that contribute to the pathogenicity of V. mali by differentially regulating external acidification capacity. Overall, our findings show that VmPma1 plays a pivotal role in pathogenicity by affecting the acidification of V. mali.