论文部分内容阅读
细菌性果斑病(Bacterial Fruit Blotch,BFB)是西瓜和甜瓜的重要病害。本实验从发病甜瓜果实上分离得到致病菌株MH21,经鉴定为燕麦食酸菌西瓜亚种(Acidovorax avenaesubsp.citrulli)。利用转座子Mini-Tn5构建MH21菌株的突变体库,Southern印迹杂交结果显示Mini-Tn5在菌株MH21染色体上可随机、单拷贝插入。通过浸种处理甜瓜种子进行突变体的致病性检查,筛选得到1株致病性完全丧失的突变体M543。对M543中转座子插入基因的克隆和测序表明其突变基因为燕麦食酸菌Ⅲ型分泌系统(TTSS)中的保守基因hrcR。推测菌株MH21中hrcR基因编码的蛋白定位于细菌内膜,是分泌通道主要成分之一。hrcR基因互补菌株的致病性检查结果显示其致病力恢复到野生型的84%。研究同时发现hrcR基因突变后MH21菌株丧失了在烟草上诱导过敏性坏死反应的能力。本研究从遗传学角度说明TTSS是西甜瓜果斑病菌致病性的重要因子。
Bacterial Fruit Blotch (BFB) is an important disease of watermelon and melon. In this experiment, the pathogenic strain MH21 was isolated from the diseased melon fruit and identified as Acidovorax avenaesubsp. Citrulli. The mutant library of MH21 strain was constructed by using the transposon Mini-Tn5. Southern blot hybridization showed that Mini-Tn5 could be randomly and single-copy inserted on chromosome MH21. The pathogenicity test of mutants was carried out by soaking melon seeds, and one mutant M543 with complete pathogenicity was screened out. Cloning and sequencing of the M543 transposon insertion gene showed that the mutant gene was a conserved gene hrcR in the oat type Ⅲ secretion system (TTSS). It is speculated that the protein encoded by the hrcR gene in strain MH21 is located in the bacterial endometrium and is one of the major components of the secretory channel. The pathogenicity test results of complementary strains of hrcR gene showed that their pathogenicity recovered to 84% of the wild type. The study also found that the MH21 strain lost the ability to induce allergic necrosis on tobacco after hrcR gene mutation. This study shows that TTSS is an important factor in the pathogenicity of Cucurbita viciiflora from the genetic point of view.