Jiang Jia, Zou Huasong, Li Yurong, Chen Gongyou
Key Laboratory of Monitoring and Management for Plant Diseases and Insects, Ministry of Agriculture, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China.
Wei Sheng Wu Xue Bao. 2009 Aug;49(8):1018-25.
The hrp (hypersensitive response on nonhost plants and pathogenicity in host plants) gene cluster, which conforms Xanthomonas oryzae pv. oryzicola, the causal agent of bacterial leaf streak in rice, to the ability to elicit a hypersensitive response (HR) in nonhost tobacco and pathogenicity in host rice, is thought to be regulated by the hrpG and hrpX genes. However, it is unclear whether the hrpG and hrpX genes regulate all the hrp gene expression of the cluster coordinately or not.
We constructed a mutant with both hrpG and hrpX genes knocked out.
which, as the same as the single mutant at the hrpG or hrpX gene, lost the ability to trigger HR in tobacco and pathogenicity in rice, respectively. Correspondingly, the hrpG and hrpX genes together could restore such the ability to the double mutant at the hrpG and hrpX loci. After grew in rice suspension cells, hrp-inducing medium XOM3 and nutrient-rich medium NB for 16 hours, respectively, reverse transcriptional polymerase chain reaction (RT-PCR) revealed that: the expression of hrp genes in NB medium was lower that that in rice cells and XOM3 medium; in whatever growth media, the hrcC, hrcT, hrpE and hpa3 genes expressed, while the hpa1, hpa2, hpaB, hrcJ, and hrpG genes did not in the hrpG mutant; the hpa2, hrcC, hpa3, hrpE and hrpG genes expressed, while the hpa1, hrcT, hpaB and hrcJ genes did not in the hrpX mutant; the hrcC, hrpE and hpa3 genes expressed, but the hpa1, hpa2, hpaB, hrcT, hrcJ and hrpG genes did not in the hrpG and hrpX double mutant.
This indicated that the expression of the hrcC, hrpE and hpa3 genes was not regulated by the hrpG and/or hrpX genes, but the expression of the hrcT gene was negatively controlled by the hrpG gene. Thus, we postulated that the expression of key type- III secretion (T3S) apparatus components was controlled by an unknown signaling pathway, which may facilitate our further understanding on the formation of the T3S machine.
hrp（非寄主植物上的过敏反应和寄主植物上的致病性）基因簇使水稻细菌性条斑病的病原菌——水稻黄单胞菌稻生致病变种具备在非寄主烟草中引发过敏反应（HR）以及在寄主水稻中致病的能力，该基因簇被认为受hrpG和hrpX基因调控。然而，尚不清楚hrpG和hrpX基因是否协同调控该基因簇中所有hrp基因的表达。
我们构建了一个hrpG和hrpX基因均被敲除的突变体。
该突变体与hrpG或hrpX基因的单突变体一样，分别丧失了在烟草中引发HR和在水稻中致病的能力。相应地，hrpG和hrpX基因共同作用可使hrpG和hrpX基因座的双突变体恢复这种能力。在水稻悬浮细胞、hrp诱导培养基XOM3和营养丰富的培养基NB中分别培养16小时后，逆转录聚合酶链反应（RT-PCR）结果显示：hrp基因在NB培养基中的表达低于在水稻细胞和XOM3培养基中的表达；无论在何种生长培养基中，hrcC、hrcT、hrpE和hpa3基因均表达，而hpa1、hpa2、hpaB、hrcJ和hrpG基因在hrpG突变体中不表达；hpa2、hrcC、hpa3、hrpE和hrpG基因表达，而hpa1、hrcT、hpaB和hrcJ基因在hrpX突变体中不表达；hrcC、hrpE和hpa3基因表达，但hpa1、hpa2、hpaB、hrcT、hrcJ和hrpG基因在hrpG和hrpX双突变体中不表达。
这表明hrcC、hrpE和hpa3基因的表达不受hrpG和/或hrpX基因调控，但hrcT基因的表达受hrpG基因负调控。因此，我们推测关键的III型分泌（T3S）装置组件的表达受未知信号通路控制，这可能有助于我们进一步了解T3S机器的形成。
