A Novel Regulatory Role of HrpD6 in Regulating hrp-hrc-hpa Genes in Xanthomonas oryzae pv. oryzicola
A Novel Regulatory Role of HrpD6 in Regulating hrp-hrc-hpa Genes in Xanthomonas oryzae pv. oryzicola
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HrpD6 在调节米黄单胞菌 hrp-hrc-hpa 基因中的新调控作用。
DOI：
10.1094/mpmi-09-10-0205
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发表时间：
2011-09-01
影响因子：
3.5
通讯作者：
Chen, Gong-You
中科院分区：
文献类型：
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作者：
Li, Yu-Rong;Zou, Hua-Song;Chen, Gong-You
米黄单胞菌。oryzicola是模式植物水稻细菌性叶斑病的致病因子，具有超敏反应和致病性（hrp），酶保守（hrc），酶相关（hpa）簇（hrp-hrc-hpa），编码III型分泌系统（T3SS），通过T3SS效应物注入宿主细胞引起疾病或触发植物防御。这一簇的突变通常会破坏细菌在非寄主烟草上引起过敏反应和在寄主水稻上引起致病性的能力。在黄单胞菌中，这些基因通常被认为是由关键的主调控因子HrpG和HrpX调控的。然而，我们提供的证据表明，除了HrpG和HrpX， HrpD6也参与调节hrp基因的表达。有趣的是，hpa2、hpa1、hpaB、hrcC和hrcT的表达受HrpD6的正调控。转录表达分析表明，hrcC、hrpD5、hrpE和hpa3基因的表达并未被hrpG和hrpX突变完全消除。通过对其对应突变体的分析发现，HrpG和HrpX表现出截然不同的基因调控，尤其是hpa2和hrcT。其他双组分系统调节因子（Zur、LrpX、ColR/S和Trh）不能完全抑制hrcC、hrpD5、hrpE和hpa3的表达。免疫印迹分析显示，HrpF的分泌不受hrpD6突变的影响。HrpF是一种与hbab无关的易位子。然而，hrpD6的突变会影响hbab依赖性TAL效应物AvrXa27的分泌。这些新发现提示，除了HrpG和HrpX外，HrpD6不仅在hrp基因调控中起重要作用，而且在TAL效应物的分泌中也起重要作用。
Xanthomonas oryzae pv. oryzicola, the causal agent of bacterial leaf streak in the model plant rice, possesses a hypersensitive response and pathogenicity (hrp), hrp-conserved (hrc), hrp-associated (hpa) cluster (hrp-hrc-hpa) that encodes a type III secretion system (T3SS) through which T3SS effectors are injected into host cells to cause disease or trigger plant defenses. Mutations in this cluster usually abolish the bacterial ability to cause hypersensitive response in nonhost tobacco and pathogenicity in host rice. In Xanthomonas spp., these genes are generally assumed to be regulated by the key master regulators HrpG and HrpX. However, we present evidence that, apart from HrpG and HrpX, HrpD6 is also involved in regulating the expression of hrp genes. Interestingly, the expression of hpa2, hpa1, hpaB, hrcC, and hrcT is positively controlled by HrpD6. Transcriptional expression assays demonstrated that the expression of the hrcC, hrpD5, hrpE, and hpa3 genes was not completely abolished by hrpG and hrpX mutations. As observed in analysis of their corresponding mutants, HrpG and HrpX exhibit contrasting gene regulation, particularly for hpa2 and hrcT. Other two-component system regulators (Zur, LrpX, ColR/S, and Trh) did not completely inhibit the expression of hrcC, hrpD5, hrpE, and hpa3. Immunoblotting assays showed that the secretion of HrpF, which is an HpaB-independent translocator, is not affected by the mutation in hrpD6. However, the mutation in hrpD6 affects the secretion of an HpaB-dependent TAL effector, AvrXa27. These novel findings suggest that, apart from HrpG and HrpX, HrpD6 plays important roles not only in the regulation of hrp genes but also in the secretion of TAL effectors.