School of Life Sciences, Sichuan Agricultural University, Ya'an, 625014, China.
Planta. 2020 Oct 15;252(5):88. doi: 10.1007/s00425-020-03484-1.
Xanthomonas campestris pv. campestris 8004 secretes several effector proteins that interfere with plant phosphorylation. Xanthomonas campestris pv. campestris (Xcc) can infect cruciferous plants and cause black rot. The strain Xcc8004 secretes effector proteins that interfere with plant cellular processes into host cells using a type III secretion (T3S) system. Several of the 24 predicted T3S effectors in the Xcc8004 genome have been implicated in the suppression of the Arabidopsis thaliana pattern-triggered immunity (PTI) response. We used an A. thaliana mesophyll protoplast-based assay to identify Xcc8004 T3S effectors that effectively interfere with PTI signalling induced by the bacterial peptide flg22. 11 of the 24 tested effector proteins (XopK, XopQ, HrpW, XopN, XopAC, XopD, XopZ1, XopAG, AvrBs2, XopL and XopX-1) inhibited expression of the flg22-inducible gene FRK1, and five effectors (XopK, XopG, XopQ, XopL and XopX-1) inhibited the expression of the flg22-inducible gene WRKY33. Therefore, there are 12 effector proteins that can inhibit the expression of relevant flg22-inducible genes. It was further investigated whether the 12 effector proteins affect the phosphorylation activation of mitogen-activated protein (MAP) kinases MPK3/MPK6, and four effector proteins (XopK, XopQ, XopZ1 and XopX-1) were found to markedly inhibit MPK3/MPK6 activation. Moreover, a subcellular localisation analysis revealed that the tested effectors were localised within various subcellular compartments. These results indicate that multiple T3S effectors in the Xcc8004 genome interfere with flg22-induced PTI signalling via various molecular mechanisms.
黄单胞菌野油菜致病变种 8004 分泌几种效应蛋白，干扰植物磷酸化。野油菜黄单胞菌野油菜亚种（Xcc）可感染十字花科植物并引起黑腐病。菌株 Xcc8004 使用 III 型分泌系统（T3S）将干扰植物细胞过程的效应蛋白分泌到宿主细胞中。Xcc8004 基因组中预测的 24 个 T3S 效应子中的几个已被牵连到拟南芥模式触发免疫（PTI）反应的抑制中。我们使用拟南芥叶肉原生质体测定法来鉴定 Xcc8004 T3S 效应子，这些效应子可有效干扰由细菌肽 flg22 诱导的 PTI 信号。在 24 种测试的效应蛋白中，有 11 种（XopK、XopQ、HrpW、XopN、XopAC、XopD、XopZ1、XopAG、AvrBs2、XopL 和 XopX-1）抑制了 flg22 诱导基因 FRK1 的表达，而 5 种效应子（XopK、XopG、XopQ、XopL 和 XopX-1）抑制了 flg22 诱导基因 WRKY33 的表达。因此，有 12 种效应蛋白可以抑制相关 flg22 诱导基因的表达。进一步研究了这 12 种效应蛋白是否影响丝裂原激活蛋白（MAP）激酶 MPK3/MPK6 的磷酸化激活，发现其中 4 种效应蛋白（XopK、XopQ、XopZ1 和 XopX-1）可显著抑制 MPK3/MPK6 的激活。此外，亚细胞定位分析表明，所测试的效应子定位于各种亚细胞隔室中。这些结果表明，Xcc8004 基因组中的多种 T3S 效应子通过多种分子机制干扰 flg22 诱导的 PTI 信号。
