Teper Doron, Burstein David, Salomon Dor, Gershovitz Michael, Pupko Tal, Sessa Guido
Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv, 69978, Israel.
Department of Cell Research and Immunology, Tel Aviv University, Tel Aviv, 69978, Israel.
Mol Plant Pathol. 2016 Apr;17(3):398-411. doi: 10.1111/mpp.12288. Epub 2015 Aug 15.
The Gram-negative bacterium Xanthomonas euvesicatoria (Xcv) is the causal agent of bacterial spot disease in pepper and tomato. Xcv pathogenicity depends on a type III secretion (T3S) system that delivers effector proteins into host cells to suppress plant immunity and promote disease. The pool of known Xcv effectors includes approximately 30 proteins, most identified in the 85-10 strain by various experimental and computational techniques. To identify additional Xcv 85-10 effectors, we applied a genome-wide machine-learning approach, in which all open reading frames (ORFs) were scored according to their propensity to encode effectors. Scoring was based on a large set of features, including genomic organization, taxonomic dispersion, hypersensitive response and pathogenicity (hrp)-dependent expression, 5' regulatory sequences, amino acid composition bias and GC content. Thirty-six predicted effectors were tested for translocation into plant cells using the hypersensitive response (HR)-inducing domain of AvrBs2 as a reporter. Seven proteins (XopAU, XopAV, XopAW, XopAP, XopAX, XopAK and XopAD) harboured a functional translocation signal and their translocation relied on the HrpF translocon, indicating that they are bona fide T3S effectors. Remarkably, four belong to novel effector families. Inactivation of the xopAP gene reduced the severity of disease symptoms in infected plants. A decrease in cell death and chlorophyll content was observed in pepper leaves inoculated with the xopAP mutant when compared with the wild-type strain. However, populations of the xopAP mutant in infected leaves were similar in size to those of wild-type bacteria, suggesting that the reduction in virulence was not caused by impaired bacterial growth.
革兰氏阴性细菌黄单胞菌（Xanthomonas euvesicatoria，Xcv）是辣椒和番茄细菌性斑点病的病原体。Xcv的致病性取决于III型分泌（T3S）系统，该系统将效应蛋白传递到宿主细胞中，以抑制植物免疫并促进疾病发生。已知的Xcv效应蛋白库包括大约30种蛋白质，其中大多数是通过各种实验和计算技术在85-10菌株中鉴定出来的。为了鉴定更多的Xcv 85-10效应蛋白，我们应用了一种全基因组机器学习方法，其中所有开放阅读框（ORF）根据其编码效应蛋白的倾向进行评分。评分基于大量特征，包括基因组组织、分类分布、过敏反应和致病性（hrp）依赖性表达、5'调控序列、氨基酸组成偏差和GC含量。使用AvrBs2的过敏反应（HR）诱导结构域作为报告基因，对36种预测的效应蛋白进行了转运到植物细胞中的测试。七种蛋白质（XopAU、XopAV、XopAW、XopAP、XopAX、XopAK和XopAD）具有功能性转运信号，它们的转运依赖于HrpF转运体，表明它们是真正的T3S效应蛋白。值得注意的是，其中四种属于新的效应蛋白家族。xopAP基因的失活降低了受感染植物中疾病症状的严重程度。与野生型菌株相比，接种xopAP突变体的辣椒叶片中细胞死亡和叶绿素含量降低。然而，感染叶片中xopAP突变体的数量与野生型细菌的数量相似，这表明毒力的降低不是由细菌生长受损引起的。
