Verma Geeta, Mondal Kalyan K, Kulshreshtha Aditya, Sharma Manju
1Division of Plant Pathology, ICAR-Indian Agricultural Research Institute, Pusa Campus, New Delhi, 110012 India.
2Amity Institute of Biotechnology, Amity University, Manesar, Gurgaon, Haryana India.
3 Biotech. 2019 Jul;9(7):272. doi: 10.1007/s13205-019-1802-9. Epub 2019 Jun 18.
pv. (Xoo) causes bacterial blight disease that limits the rice production globally. The bacterium secretes effector proteins directly into plant cells through a type III secretion system (T3SS). Here, we examined the role of a conserved XopR T3SS-effector in the suppression of host basal defense response. Phylogenetic and sequence analysis showed that XopR is well conserved within Xoo strains but shares varying degree of similarity among the other species. The expression of XopR was shown to be regulated by , a key regulator of cluster. For functional analysis we employed two mutant strains of Xoo, one lacks gene and other lacks gene (making the strain defective in T3SS). Programmed cell death (PCD) events was examined both in rice and tobacco leaves through trypan blue staining method. In XopR expressing tobacco leaves the PCD induction was compromised. We observed higher PCD on rice leaves inoculated with Xoo mutants lacking either or functional T3SS as compared to wild type. Contrary, when gene was complemented in mutated strain the PCD was suppressed which clearly suggests that XopR acts as suppressor of the PCD mediated defense response. The EYFP::XopR fusion protein was shown to be localized to the plasma membrane of and onion epidermal cells. Altogether our study leads to the understanding that XopR T3SS-effector is essential for Xoo to suppress PCD, primarily to support the in planta colonization of Xoo during blight pathogenesis.
稻黄单胞菌（Xoo）引发的白叶枯病限制了全球水稻产量。该细菌通过III型分泌系统（T3SS）将效应蛋白直接分泌到植物细胞中。在此，我们研究了保守的XopR T3SS效应蛋白在抑制宿主基础防御反应中的作用。系统发育和序列分析表明，XopR在Xoo菌株中高度保守，但在其他物种中相似度不同。结果显示，XopR的表达受hrp簇的关键调节因子调控。为进行功能分析，我们使用了两种Xoo突变菌株，一种缺失hrp基因，另一种缺失hrc基因（使该菌株在T3SS方面存在缺陷）。通过台盼蓝染色法在水稻和烟草叶片中检测程序性细胞死亡（PCD）事件。在表达XopR的烟草叶片中，PCD诱导受到抑制。与野生型相比，我们观察到接种缺乏hrp或功能性T3SS的Xoo突变体的水稻叶片上PCD更高。相反，当在突变菌株中互补hrp基因时，PCD受到抑制，这清楚地表明XopR作为PCD介导的防御反应的抑制因子发挥作用。EYFP::XopR融合蛋白被证明定位于烟草和洋葱表皮细胞的质膜。总之，我们的研究表明，XopR T3SS效应蛋白对于Xoo抑制PCD至关重要，主要是为了在白叶枯病发病过程中支持Xoo在植物体内的定殖。
