Candidate effector proteins of the necrotrophic apple canker pathogen Valsa mali can suppress BAX-induced PCD

Abstract

Canker caused by the Ascomycete Valsa mali is the most destructive disease of apple in Eastern Asia, resulting in yield losses of up to 100%. This necrotrophic fungus induces severe necrosis on apple, eventually leading to the death of the whole tree. Identification of necrosis inducing factors may help to unravel the molecular bases for colonization of apple trees by V. mali. As a first step toward this goal, we identified and characterized the V. mali repertoire of candidate effector proteins (CEPs). In total, 193 secreted proteins with no known function were predicted from genomic data, of which 101 were V. mali-specific. Compared to non-CEPs predicted for the V. mali secretome, CEPs have shorter sequence length and a higher content of cysteine residues. Based on transient over-expression in Nicotiana benthamiana performed for 70 randomly selected CEPs, seven V. mali Effector Proteins (VmEPs) were shown to significantly suppress BAX-induced PCD. Furthermore, targeted deletion of VmEP1 resulted in a significant reduction of virulence. These results suggest that V. mali expresses secreted proteins that can suppress PCD usually associated with effector-triggered immunity (ETI). ETI in turn may play an important role in the V. mali–apple interaction. The ability of V. mali to suppress plant ETI sheds a new light onto the interaction of a necrotrophic fungus with its host plant.

A small cysteine‐rich protein from two kingdoms of microbes is recognized as a novel pathogen‐associated molecular pattern

“…For generation of VmE02 deletion mutants in V. mali, transformed V. mali lines were obtained using polyethylene glycol (PEG)-mediated protoplast transformation (Gao et al, 2011), according to a method described previously ( Fig. S1; Li et al, 2015). Positive transformants were screened using genomic PCR with the primers listed in Table S1, which were further confirmed by Southern blotting using the DIG DNA Labeling and Detection Kit II (Roche, Mannheim, Germany) according to the manufacturer's instructions.…”

Two members of the velvet family, VmVeA and VmVelB, affect conidiation, virulence and pectinase expression in Valsa mali

“…Valsa mali is an ascomycete which causes Apple Valsa Canker (AVC). The disease is very important for apple production in eastern Asia, especially in China, where yield losses can reach 100% (Li et al ., ; Wang X. et al ., ). This necrotrophic pathogen mainly infects host bark by means of conidia entering through wounds (Ke et al ., ; Wang X. et al ., ).…”

The distinct roles of Argonaute protein 2 in the growth, stress responses and pathogenicity of the apple tree canker pathogen

“…Investigating the pathogenesis of V. mali is important for developing a resistance breeding strategy and for identifying new fungicide target sites; however, the molecular mechanisms underlying the pathogenesis of V. mali are complex and not fully understood. Although recent analyses of the V. mali genome and transcriptome information have provided a means to explore the pathogenesis, and some pathogenesis-related genes have been identified and characterized (Ke et al, 2014;Li et al, 2015;Yin, Zhu, Feng, & Huang, 2016;Yin et al, 2015), the RNA interference (RNAi) pathway of V. mali is still unknown.…”