Open AccessHydroxybenzoate hydroxylase genes underlying protocatechuic acid production in Valsa mali are required for full pathogenicity in apple trees
Author(s) -
Meng Lulu,
Sun Cuicui,
Gao Liyong,
Saleem Muhammad,
Li Baohua,
Wang Caixia
Publication year - 2021
Publication title -
molecular plant pathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.945
H-Index - 103
eISSN - 1364-3703
pISSN - 1464-6722
DOI - 10.1111/mpp.13119
Subject(s) - biology , virulence , protocatechuic acid , mutant , gene , toxin , canker , transcriptome , microbiology and biotechnology , botany , genetics , biochemistry , gene expression , antioxidant
Valsa mali is the causative agent of apple tree valsa canker, which causes significant losses in apple production. It produces various toxic compounds that kill plant cells, facilitating infection. Among these, protocatechuic acid exhibits the highest phytotoxic activity. However, those genes involved in toxin production have not been studied. In this study we identified four hydroxybenzoate hydroxylase genes ( VmHbh1 , VmHbh2 , VmHbh3 , and VmHbh4 ) from the transcriptome of V . mali . The VmHbh protein had high enzymatic activities of hydroxybenzoate hydroxylase, which could convert 4‐hydroxybenzoate to protocatechuic acid. These four VmHbh genes all had highly elevated transcript levels during the V . mali infection process, especially VmHbh1 and VmHbh4 , with 26.0‐ and 53.4‐fold increases, respectively. Mutants of the four genes were generated to study whether VmHbh s are required for V . mali pathogenicity. Of the four genes, the VmHbh1 and VmHbh4 deletion mutants considerably attenuated V . mali virulence in apple leaves and in twigs, coupled with much reduced toxin levels. The VmHbh2 and VmHbh3 deletion mutants promoted the transcript levels of the other VmHbh s, suggesting functional redundancies of VmHbh s in V . mali virulence. The results provide insights into the functions of VmHbhs in the production of protocatechuic acid by V . mali during its infection of apple trees.