Hyytiäinen H, Montesano M, Palva E T
Department of Biosciences, University of Helsinki, Finland.
Mol Plant Microbe Interact. 2001 Aug;14(8):931-8. doi: 10.1094/MPMI.2001.14.8.931.
The production of the main virulence determinants, the extracellular plant cell wall-degrading enzymes, and hence virulence of Erwinia carotovora subsp. carotovora is controlled by a complex regulatory network. One of the global regulators, the response regulator ExpA, a GacA homolog, is required for transcriptional activation of the extracellular enzyme genes of this soft-rot pathogen. To elucidate the mechanism of ExpA control as well as interactions with other regulatory systems, we isolated second-site transposon mutants that would suppress the enzyme-negative phenotype of an expA (gacA) mutant. Inactivation of kdgR resulted in partial restoration of extracellular enzyme production and virulence to the expA mutant, suggesting an interaction between the two regulatory pathways. This interaction was mediated by the RsmA-rsmB system. Northern analysis was used to show that the regulatory rsmB RNA was under positive control of ExpA. Conversely, the expression of rsmA encoding a global repressor was under negative control of ExpA and positive control of KdgR. This study indicates a central role for the RsmA-rsmB regulatory system during pathogenesis, integrating signals from the ExpA (GacA) and KdgR global regulators of extracellular enzyme production in E. carotovora subsp. carotovora.
胡萝卜软腐欧文氏菌胡萝卜软腐亚种主要毒力决定因子（即细胞外植物细胞壁降解酶）的产生以及毒力受一个复杂的调控网络控制。全局调控因子之一，应答调控因子ExpA（GacA的同源物），是这种软腐病原菌细胞外酶基因转录激活所必需的。为了阐明ExpA的调控机制以及与其他调控系统的相互作用，我们分离了能抑制expA（gacA）突变体酶阴性表型的第二位点转座子突变体。kdgR的失活导致expA突变体细胞外酶产生和毒力部分恢复，表明这两条调控途径之间存在相互作用。这种相互作用由RsmA-rsmB系统介导。Northern分析表明调控性rsmB RNA受ExpA的正调控。相反，编码全局阻遏物的rsmA的表达受ExpA的负调控和KdgR的正调控。本研究表明RsmA-rsmB调控系统在致病过程中起核心作用，整合了来自胡萝卜软腐欧文氏菌胡萝卜软腐亚种细胞外酶产生的ExpA（GacA）和KdgR全局调控因子的信号。
