Deng Xin, Xiao Yanmei, Lan Lefu, Zhou Jian-Min, Tang Xiaoyan
Department of Plant Pathology, Kansas State University, Manhattan, KS 66506-5502, USA.
Mol Plant Microbe Interact. 2009 Aug;22(8):964-76. doi: 10.1094/MPMI-22-8-0964.
Pseudomonas syringae bacteria utilize the type III secretion system (T3SS) to deliver effector proteins into host cells. The T3SS and T3 effector genes (together called the T3 genes hereafter) are repressed in nutrient-rich medium but rapidly induced after the bacteria are transferred into minimal medium or infiltrated into plants. The induction of the T3 genes is mediated by HrpL, an alternative sigma factor that recognizes the conserved hrp box motif in the T3 gene promoters. The induction of hrpL is mediated by HrpR and HrpS, two homologous proteins that bind the hrpL promoter. To identify additional genes involved in regulation of the T3 genes, we screened for the P. syringae pv. phaseolicola NPS3121 transposon-tagged mutants with reduced induction of avrPto-luc and hrpL-luc, reporter genes for promoters of effector gene avrPto and hrpL, respectively. Determination of the transposon-insertion sites revealed genes with putative functions in signal transduction and transcriptional regulation, protein synthesis, and basic metabolism. A transcriptional regulator (AefR(NPS3121)) was identified in our screen that is homologous to AefR of P. syringae pv. syringae strain B728a, a regulator of the quorum-sensing signal and epiphytic traits, but was not known to regulate the T3 genes. AefR(NPS3121) in P. syringae pv. phaseolicola NPS3121 and AefR in P. syringae pv. syringae B728a behave similarly in regulating the quorum-sensing signal in liquid medium but differ in regulating the epiphytic traits, including swarming motility, leaf entry, and epiphytic survival.
丁香假单胞菌利用Ⅲ型分泌系统（T3SS）将效应蛋白输送到宿主细胞中。T3SS和T3效应基因（以下统称为T3基因）在营养丰富的培养基中受到抑制，但在细菌转移到基本培养基中或浸润到植物中后会迅速被诱导表达。T3基因的诱导由HrpL介导，HrpL是一种替代σ因子，可识别T3基因启动子中的保守hrp框基序。HrpL的诱导由HrpR和HrpS介导，这两种同源蛋白可结合hrpL启动子。为了鉴定参与T3基因调控的其他基因，我们筛选了菜豆丁香假单胞菌NPS3121的转座子标签突变体，这些突变体中效应基因avrPto和hrpL启动子的报告基因avrPto-luc和hrpL-luc的诱导水平降低。转座子插入位点的测定揭示了在信号转导和转录调控、蛋白质合成以及基础代谢中具有推定功能 的基因。我们在筛选中鉴定出一种转录调节因子（AefR(NPS3121)），它与丁香假单胞菌丁香致病变种B728a的AefR同源，后者是群体感应信号和附生性状的调节因子，但此前未知其可调控T3基因。菜豆丁香假单胞菌NPS3121中的AefR(NPS3121)和丁香假单胞菌丁香致病变种B728a中的AefR在调节液体培养基中的群体感应信号方面表现相似，但在调节包括群体游动、叶片侵入和附生存活等附生性状方面存在差异。
