Harris S J, Shih Y L, Bentley S D, Salmond G P
Department of Biochemistry, University of Cambridge, UK.
Mol Microbiol. 1998 May;28(4):705-17. doi: 10.1046/j.1365-2958.1998.00825.x.
We have identified a gene important for the regulation of exoenzyme virulence factor synthesis in the plant pathogen Erwinia carotovora ssp. carotovora (Ecc) and virulence and motility in Erwinia carotovora ssp. atroseptica (Eca). This gene, hexA (hyperproduction of exoenzymes), is a close relative of the Erwinia chrysanthemi (Echr) gene pecT and encodes a member of the LysR family of transcriptional regulators. hexA mutants in both Ecc and Eca produce abnormally high levels of the exoenzyme virulence factors pectate lyase, cellulase and protease. In addition, Eca hexA mutants show increased expression of the fliA and fliC genes and hypermotility. Consistent with a role as a global regulator, expression of hexA from even a low-copy plasmid can suppress exoenzyme production in Ecc and Eca and motility in Eca. Production of the quorum-sensing pheromone OHHL in Ecc hexA is higher throughout the growth curve compared with the wild-type strain. Overexpression of Ecc hexA also caused widespread effects in several strains of the opportunistic human pathogen, Serratia. Low-copy hexA expression resulted in repression of exoenzyme, pigment and antibiotic production and repression of the spreading phenotype. Finally, mutations in hexA were shown to increase Ecc or Eca virulence in planta.
我们已经鉴定出一个基因，它对于植物病原菌胡萝卜软腐欧文氏菌胡萝卜软腐亚种（Ecc）中外酶毒力因子合成的调控很重要，并且对胡萝卜软腐欧文氏菌黑胫亚种（Eca）的毒力和运动性也很重要。这个基因，hexA（外酶超量产生），是菊欧文氏菌（Echr）基因pecT的近亲，编码一个转录调节因子的LysR家族成员。Ecc和Eca中的hexA突变体产生异常高水平的外酶毒力因子果胶酸裂解酶、纤维素酶和蛋白酶。此外，Eca hexA突变体显示fliA和fliC基因的表达增加以及运动性增强。与作为全局调节因子的作用一致，即使是低拷贝质粒中的hexA表达也能抑制Ecc和Eca中的外酶产生以及Eca中的运动性。与野生型菌株相比，Ecc hexA中群体感应信息素OHHL在整个生长曲线中的产生都更高。Ecc hexA的过表达在机会性人类病原菌沙雷氏菌的几个菌株中也引起了广泛的影响。低拷贝hexA表达导致外酶、色素和抗生素产生的抑制以及扩散表型的抑制。最后，hexA中的突变显示会增加Ecc或Eca在植物中的毒力。
