柑橘溃疡病菌胞外蛋白水解酶对其致病力的作用

The role of extracellular protease on the virulence of Xanthomonas citri subsp. citri

采用异源表达方法从柑橘黄单胞柑橘亚种(Xcc)中国菌株Xcc 29-1中鉴定出6个编码胞外蛋白水解酶的基因.运用同源重组方法将6个编码基因全部敲除,得到胞外蛋白水解酶缺失突变体,对其致病力、形成生物膜的能力和生长繁殖速度进行检测.结果显示,蛋白水解酶突变体在柑橘上的致病力减弱,并且附着到试管壁的细菌数量显著减少,形成生物膜的能力下降.在野生型菌株中过表达蛋白水解酶后,形成的溃疡病斑水渍状程度加大,在柑橘中的繁殖速度变快;在柑橘叶片中,6个胞外蛋白水解酶基因的转录水平都增强表达.这些结果表明Xcc的胞外蛋白水解酶是一个重要的致病因子.

Six extracellular protease coding genes were identified from Xanthomonas citri subsp.citri(Xcc)Chinese strain 29-1 using heterologous expression strategy.Then an extracellular protease mutant with the deletion of all six coding genes was obtained by homologous recombination method.Its virulence and growth rate,and the capacity to produce biofim were tested.The mutant showed a complete loss of extracellular protease activity and an attenuated virulence on citrus plants.The cell number attached to glass tube wall decreased remarkably,implying a reduced ability to form biofilm.Over-expression of proteases in wild-type Xcc 29-1 resulted in a deteriorative water-soaking symptom in citrus plants,as well as an increased proliferation rate within citrus tissue.In citrus leaves,the transcription levels of 6 extracellular protease genes were enhanced.In conclusion,the extracellular protease is an important virulence factor for Xcc infection.