柑橘溃疡病菌II型分泌通道基因xpsD突变体的鉴定及功能分析

【目的】鉴定柑橘溃疡病菌胞外水解酶减弱突变体Mxac56-20的Tn5插入位点，及其在柑橘上的致病力。【方法】采用质粒拯救方法获得Tn5旁侧序列，与基因组信息比对后明确突变体的插入位点；构建功能互补载体对突变体进行功能互补，检测互补菌株胞外蛋白水解酶、纤维素酶和淀粉酶的恢复情况；在寄主植物柑橘上观察致病力变化。【结果】Mxac56-20的Tn5插入位点是II型分泌系统xpsD基因，所构建的互补载体使突变体的胞外水解酶活性和致病力得到恢复。【结论】柑橘溃疡病菌xpsD基因的突变，导致胞外水解酶活性降低，在寄主上的致病力减弱，说明柑橘溃疡病菌的II型分泌系统在与寄主互作过程中起到致病因子的作用。

Functional characterization of the general secretion pathway xpsD gene in Xanthomonas citri subsp. citri

Objective] The purpose of this work was to identify the insertion site of mutant Mxac56-20 with reduced extracellular enzyme activities, and to characterize the function of the mutated gene. Methods] The Tn5 flanking sequence was identified by using plasmid rescue method. After the complementary recombinant was constructed, the restorations of extracellular enzyme and pathogenicity on host plant were tested. Results] Tn5 transposon was inserted in the general secretion pathway xpsD gene in Xanthomonas citri subsp. citri. The phenotypic alterations were restored when constitutively expressing xpsD gene in mutant Mxac56-20. Conclusion] The mutagenesis of xpsD gene in X. citri subsp. citri led to the reductions in extracellular enzyme activities and pathogenicity on host plant. These collected data demonstrated that the general secretion pathway is required for full virulence on host plant by X. citri subsp. citri.