Yap Mee-Ngan, Yang Ching-Hong, Charkowski Amy O
Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706, USA.
Mol Plant Microbe Interact. 2008 Mar;21(3):304-14. doi: 10.1094/MPMI-21-3-0304.
HrpX/Y is a putative two-component system (TCS) encoded within the type III secretion system (T3SS) gene cluster of Dickeya dadantii. A linear regulatory cascade initiated by HrpX/Y that leads to activation of the downstream T3SS genes via HrpS and HrpL was described previously. Therefore, in D. dadantii, HrpX/Y plays an important role in regulation of genes involved in bacteria-plant interactions and bacterial aggregation via the T3SS. HrpX/Y is the only TCS shared among the plant-pathogenic enterobacteria that is not also present in animal-associated enterobacteria. To date, the genes known to be regulated by HrpY are restricted to the hrp and hrc genes and no signal has been identified that triggers HrpY-dependent gene expression. We demonstrated that HrpY interacts with the hrpS promoter in vitro. We then used a transposon-based system to isolate previously unidentified HrpY-dependent genes, including genes previously shown to affect virulence, including kdgM and acsC. HrpY is a dual regulator, positively regulating at least 10 genes in addition to those in the hrp gene cluster and negatively regulating at least 5 genes. The regulatory effect on one gene depended on the culture medium used. Of the 16 HrpY-regulated genes identified in this screen, 14 are not present in Pectobacterium atrosepticum, the nearest relative of D. dadantii with a sequenced genome. None of the newly identified HrpY-regulated genes were required for bacterial aggregation; thus, neither acyl-homoserine lactone-mediated quorum sensing nor the Rcs signal transduction system which regulates colanic acid, a molecule that plays an important role in biofilm formation in other enterobacteria, are required for D. dadantii aggregation.
HrpX/Y是一个假定的双组分系统（TCS），由达旦氏果胶杆菌（Dickeya dadantii）的III型分泌系统（T3SS）基因簇编码。先前已描述了由HrpX/Y启动的线性调控级联反应，该反应通过HrpS和HrpL导致下游T3SS基因的激活。因此，在达旦氏果胶杆菌中，HrpX/Y通过T3SS在调控参与细菌-植物相互作用和细菌聚集的基因方面发挥重要作用。HrpX/Y是植物致病性肠道细菌中唯一共享的双组分系统，在与动物相关的肠道细菌中不存在。迄今为止，已知受HrpY调控的基因仅限于hrp和hrc基因，尚未鉴定出触发HrpY依赖性基因表达的信号。我们证明HrpY在体外与hrpS启动子相互作用。然后，我们使用基于转座子的系统来分离先前未鉴定的HrpY依赖性基因，包括先前显示影响毒力的基因，如kdgM和acsC。HrpY是一种双重调节因子，除了hrp基因簇中的基因外，它还正向调节至少10个基因，并负向调节至少五个基因。对一个基因的调节作用取决于所使用的培养基。在该筛选中鉴定出的16个受HrpY调控的基因中，有14个在黑胫果胶杆菌（Pectobacterium atrosepticum）中不存在，黑胫果胶杆菌是达旦氏果胶杆菌基因组已测序的最近亲缘种。新鉴定的受HrpY调控的基因均不是细菌聚集所必需的；因此，达旦氏果胶杆菌的聚集既不需要酰基高丝氨酸内酯介导的群体感应，也不需要调节结肠酸的Rcs信号转导系统，结肠酸是一种在其他肠道细菌的生物膜形成中起重要作用的分子。
