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 VmHbhs 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 VmHbhs, suggesting functional redundancies of VmHbhs 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.

中文翻译：

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马里瓦尔萨原儿茶酸产生的羟基苯甲酸羟化酶基因是苹果树完全致病性所必需的

Valsa mali是苹果树 valsa 溃疡病的病原体，导致苹果生产的重大损失。它产生多种有毒化合物，可杀死植物细胞，促进感染。其中，原儿茶酸表现出最高的植物毒性活性。然而，那些与毒素产生有关的基因还没有被研究过。在这项研究中，我们从V的转录组中鉴定了四个羟基苯甲酸羟化酶基因（VmHbh1、VmHbh2、VmHbh3和VmHbh4 ） 。 马里_ VmHbh蛋白具有较高的羟基苯甲酸羟化酶酶活性，可将4-羟基苯甲酸转化为原儿茶酸。这四个VmHbh基因在V期间都具有高度升高的转录水平。 马里感染过程，尤其是VmHbh1和VmHbh4，分别增加了 26.0 倍和 53.4 倍。产生四个基因的突变体以研究VmHbh s是否是V所必需的。 马里致病性。在四个基因中，VmHbh1和VmHbh4缺失突变体显着减弱了 V。苹果叶和树枝中的马里毒力，加上大大降低的毒素水平。VmHbh2和VmHbh3 _缺失突变体促进了其他VmHbh s 的转录水平，表明VmHbh s 在V中的功能冗余。 马里的毒力。该结果提供了对 VmHbhs 在V产生原儿茶酸中的功能的见解。 马里在感染苹果树期间。