Liu Pu, Wood Derek, Nester Eugene W
Department of Microbiology, Box 357242, University of Washington, Seattle, WA 98195-7242, USA.
J Bacteriol. 2005 Sep;187(17):6039-45. doi: 10.1128/JB.187.17.6039-6045.2005.
The pckA gene, encoding phosphoenolpyruvate carboxykinase, catalyzes the reversible decarboxylation and phosphorylation of oxaloacetate to form phosphoenolpyruvate. Located on the circular chromosome of Agrobacterium, this locus is adjacent to the loci chvG and chvI, encoding a two-component regulatory system that has been shown to be important in virulence. Using a reporter gene fusion, studies showed that the pckA gene is induced by acidic pH but not by acetosyringone. This acid induction is regulated by the chvG-chvI regulatory system, which controls acid-inducible genes. A pckA mutant had no demonstrable PckA enzyme activity and grew on AB minimal medium with glucose but did not grow on the same medium with succinate as the sole carbon source and was more inhibited in its growth than the wild-type strain by an acidic environment. A pckA mutant was highly attenuated in tumor-inducing ability on tobacco leaf disks and was severely attenuated in vir gene expression. Although vir gene induction was completely restored when a constitutive virG gene was introduced into the mutant strain, virulence was only partially restored. These results suggest that avirulence may be due to a combination of the inhibition of this mutant in the acidic plant wound environment and the poor induction of the vir genes.
编码磷酸烯醇丙酮酸羧激酶的pckA基因催化草酰乙酸的可逆脱羧和磷酸化反应，生成磷酸烯醇丙酮酸。该基因座位于农杆菌的环状染色体上，与chvG和chvI基因座相邻，chvG和chvI编码一个双组分调控系统，该系统已被证明在毒力方面很重要。通过报告基因融合实验，研究表明pckA基因是由酸性pH诱导的，而非由乙酰丁香酮诱导。这种酸诱导作用受chvG-chvI调控系统调节，该系统控制酸诱导基因。一个pckA突变体没有可检测到的PckA酶活性，它能在含有葡萄糖的AB基本培养基上生长，但不能在以琥珀酸作为唯一碳源的相同培养基上生长，并且在酸性环境中比野生型菌株生长受到更强的抑制。一个pckA突变体在烟草叶片圆盘上的致瘤能力高度减弱，并且在vir基因表达方面严重减弱。尽管当将一个组成型virG基因导入突变菌株时，vir基因诱导完全恢复，但毒力仅部分恢复。这些结果表明，无毒力可能是由于该突变体在酸性植物伤口环境中的生长受到抑制以及vir基因诱导不良共同作用的结果。
