First, second, fourth, and seventh authors; Gulf Coast and Research Education Center, Wimauma, FL; first, second, third, fifth, sixth, and seventh authors: Department of Plant Pathology, University of Florida, Gainesville; and fifth author: Emerging Pathogens Institute, University of Florida, Gainesville.
Phytopathology. 2018 Dec;108(12):1355-1362. doi: 10.1094/PHYTO-02-18-0052-R. Epub 2018 Oct 15.
Type III secretion system effectors contribute to pathogenicity through various mechanisms. Recent surveys showed an increasing prevalence of the type III secretion effector avrBsT among Xanthomonas perforans strains. We hypothesized that the acquisition of avrBsT has a fitness advantage for the pathogen. The contribution of avrBsT to fitness on tomato was evaluated based on disease severity, in planta growth, competition, and recovery rates of wild-type (WT) and avrBsT mutant strains in greenhouse and field plants. GEV872 and GEV1001, representative strains of two phylogenomic groups of X. perforans, were selected for generating avrBsT mutants. Disease severity was higher for WT strains compared with the avrBsT mutant strains. X. perforans WT and avrBsT mutant strains did not differ following leaf infiltration of greenhouse plants in direct competition and in planta growth assays. The effect of avrBsT on pathogen fitness was noticeable under field conditions. Differences in strain recovery were significant, with WT being recovered two to eight times more than avrBsT mutant strains in the case of both strains GEV872 and GEV1001. WT strains were capable of spreading longer distances across field plots compared with avrBsT mutant strains. Findings suggest that the functional AvrBsT affects the fitness of X. perforans under field conditions, making it an ideal candidate for bacterial spot resistance breeding efforts in tomato.
III 型分泌系统效应子通过各种机制促进致病性。最近的调查显示，穿孔黄单胞菌菌株中 III 型分泌效应子 avrBsT 的流行率不断上升。我们假设 avrBsT 的获得对病原体具有适应性优势。根据温室和田间植物中野生型（WT）和 avrBsT 突变株的发病严重程度、体内生长、竞争和恢复率，评估 avrBsT 对番茄适应性的贡献。选择 GEV872 和 GEV1001 这两个穿孔黄单胞菌系统发育群的代表菌株来生成 avrBsT 突变株。与 avrBsT 突变株相比，WT 菌株的发病严重程度更高。在温室植物叶片渗透的直接竞争和体内生长试验中，WT 和 avrBsT 突变株之间没有差异。在田间条件下，avrBsT 对病原体适应性的影响是明显的。WT 菌株的回收差异显著，与 avrBsT 突变株相比，在 GEV872 和 GEV1001 两种菌株的情况下，WT 菌株的回收量高出 2 到 8 倍。与 avrBsT 突变株相比，WT 菌株能够在田间更远距离传播。研究结果表明，功能型 AvrBsT 影响穿孔黄单胞菌在田间条件下的适应性，使其成为番茄细菌性斑点病抗性育种的理想候选基因。
