Type III-Dependent Translocation of HrpB2 by a Nonpathogenic hpaABC Mutant of the Plant-Pathogenic Bacterium Xanthomonas campestris pv. vesicatoria
Type III-Dependent Translocation of HrpB2 by a Nonpathogenic hpaABC Mutant of the Plant-Pathogenic Bacterium Xanthomonas campestris pv. vesicatoria
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DOI：
10.1128/aem.00537-16
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发表时间：
2016-03
影响因子：
4.4
通讯作者：
Felix Scheibner;S. Schulz;Jens Hausner;S. Marillonnet;D. Büttner
中科院分区：
文献类型：
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作者：
Felix Scheibner;S. Schulz;Jens Hausner;S. Marillonnet;D. Büttner
植物病原细菌野油菜黄单胞菌致病变种Xanthomonascampestris pv. vesicatoria利用III型分泌（T3S）系统将效应蛋白易位到植物细胞中。T3S装置跨越两种细菌膜，并与宿主质膜中的细胞外菌毛和通道样易位子相关。T3S由开关蛋白HpaC控制，其抑制预测的内杆蛋白HrpB2的分泌和易位，并促进易位子和效应蛋白的分泌。我们以前报道HrpB 2与HpaC和内膜蛋白HrcU的胞质结构域相互作用（C. Lorenz，S. Schulz，T.沃尔施岛罗西耶大学Bonas和D. Büttner，PLoS Pathog 4：e1000094，2008，http：//dx. doi. org/10. 1371/journal. ppat. 1000094）。然而，控制HrpB2分泌的分子机制尚未了解。在这里，我们在HrpB2的N-末端40个氨基酸中定位了T3S和易位信号。与HrpB2缺失衍生物的互补实验的结果表明，HrpB2的T3S信号是蛋白质功能所必需的。此外，相互作用研究表明，HrpB2的N-末端区域与HrcU的胞质结构域相互作用，表明HrpB2的T3S信号有助于底物对接。HrpB2的易位不仅受到HpaC的抑制，而且受到T3S伴侣HpaB及其分泌调节因子HpaA的抑制。hpaA、hpaB和hpaC的缺失导致致病性丧失，但允许HrpB2 T3S信号和效应蛋白之间的融合蛋白易位到宿主和非宿主植物的叶子中。重要性植物病原细菌野油菜黄单胞菌致病变种的T3S系统。vesicatoria是致病性所必需的，并将效应蛋白递送到植物细胞中。T3S依赖于HrpB2，其是分泌器的预测周质内杆结构的组分。HrpB2在分泌过程的早期阶段分泌，并与内膜蛋白HrcU的胞质结构域相互作用。在这里，我们本地化的分泌和易位信号的HrpB2的N-末端40个氨基酸，并表明，该地区是足够的相互作用与胞质结构域的HrcU。我们的研究结果表明，HrpB2的T3S信号的HrpB2的分泌装置的对接所需的。此外，我们提供的实验证据表明，HrpB2的N-末端区域是足够的目标效应蛋白易位在一个非致病性X。野油菜致病变种vesicatoria菌株
ABSTRACT The plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria employs a type III secretion (T3S) system to translocate effector proteins into plant cells. The T3S apparatus spans both bacterial membranes and is associated with an extracellular pilus and a channel-like translocon in the host plasma membrane. T3S is controlled by the switch protein HpaC, which suppresses secretion and translocation of the predicted inner rod protein HrpB2 and promotes secretion of translocon and effector proteins. We previously reported that HrpB2 interacts with HpaC and the cytoplasmic domain of the inner membrane protein HrcU (C. Lorenz, S. Schulz, T. Wolsch, O. Rossier, U. Bonas, and D. Büttner, PLoS Pathog 4:e1000094, 2008, http://dx.doi.org/10.1371/journal.ppat.1000094). However, the molecular mechanisms underlying the control of HrpB2 secretion are not yet understood. Here, we located a T3S and translocation signal in the N-terminal 40 amino acids of HrpB2. The results of complementation experiments with HrpB2 deletion derivatives revealed that the T3S signal of HrpB2 is essential for protein function. Furthermore, interaction studies showed that the N-terminal region of HrpB2 interacts with the cytoplasmic domain of HrcU, suggesting that the T3S signal of HrpB2 contributes to substrate docking. Translocation of HrpB2 is suppressed not only by HpaC but also by the T3S chaperone HpaB and its secreted regulator, HpaA. Deletion of hpaA, hpaB, and hpaC leads to a loss of pathogenicity but allows the translocation of fusion proteins between the HrpB2 T3S signal and effector proteins into leaves of host and non-host plants. IMPORTANCE The T3S system of the plant-pathogenic bacterium Xanthomonas campestris pv. vesicatoria is essential for pathogenicity and delivers effector proteins into plant cells. T3S depends on HrpB2, which is a component of the predicted periplasmic inner rod structure of the secretion apparatus. HrpB2 is secreted during the early stages of the secretion process and interacts with the cytoplasmic domain of the inner membrane protein HrcU. Here, we localized the secretion and translocation signal of HrpB2 in the N-terminal 40 amino acids and show that this region is sufficient for the interaction with the cytoplasmic domain of HrcU. Our results suggest that the T3S signal of HrpB2 is required for the docking of HrpB2 to the secretion apparatus. Furthermore, we provide experimental evidence that the N-terminal region of HrpB2 is sufficient to target effector proteins for translocation in a nonpathogenic X. campestris pv. vesicatoria strain.