Neale Helen C, Hulin Michelle T, Harrison Richard J, Jackson Robert W, Arnold Dawn L
Centre for Research in Bioscience, Faculty of Health and Applied Sciences, Frenchay Campus, The University of the West of England, Bristol BS16 1QY, UK.
NIAB EMR, East Malling ME19 6BJ, UK.
Microorganisms. 2021 Jun 18;9(6):1328. doi: 10.3390/microorganisms9061328.
Bacterial canker of , affecting economically important stone fruit crops including cherry, peach, apricot and plum, is caused by the plant pathogen (.). Strains from two pathovars- pv. () and . pv. race 1 (R1) and 2 (R2)-in three phylogenetically distant clades have convergently evolved to infect . The bacteria enter woody tissues through wounds and leaf scars, causing black necrotic cankers. Symptoms are also produced on blossom, fruit and leaves. Little is known about the mechanisms uses to colonise tree hosts such as . Here, we created transposon (Tn) mutant libraries in one strain of from each of the three clades and screened the mutants on immature cherry fruit to look for changes in virulence. Mutants (242) with either reduced or enhanced virulence were detected and further characterised by in vitro screens for biofilm formation, swarming ability, and pathogenicity on leaves and cut shoots. In total, 18 genes affecting virulence were selected, and these were involved in diverse functions including motility, type III secretion, membrane transport, amino acid synthesis, DNA repair and primary metabolism. Interestingly, mutation of the effector gene, , led to an increase in virulence of R2.
核果类细菌性溃疡病影响包括樱桃、桃、杏和李在内的具有重要经济价值的核果类作物，由植物病原菌丁香假单胞菌（Pseudomonas syringae）引起。来自三个系统发育距离较远的分支中的两个致病型——丁香假单胞菌核果致病变种（P. syringae pv. syringae）和丁香假单胞菌李致病变种1号小种（P. syringae pv. morsprunorum race 1）及2号小种（R2）——已趋同进化以感染核果类。细菌通过伤口和叶痕进入木质组织，导致黑色坏死溃疡。在花、果实和叶片上也会出现症状。关于丁香假单胞菌用于定殖如核果类树木宿主的机制知之甚少。在此，我们在来自三个分支的每一个的一株丁香假单胞菌中创建了转座子（Tn）突变体文库，并在未成熟樱桃果实上筛选突变体以寻找毒力变化。检测到毒力降低或增强的突变体（242个），并通过体外筛选生物膜形成、群体运动能力以及在叶片和切段嫩枝上的致病性进行进一步表征。总共选择了18个影响毒力的基因，这些基因涉及多种功能，包括运动性、III型分泌、膜转运、氨基酸合成、DNA修复和初级代谢。有趣的是，效应子基因hopAM1的突变导致丁香假单胞菌李致病变种2号小种（P. syringae pv. morsprunorum race 2）的毒力增加。
