Castañeda Adriana, Reddy Joseph D, El-Yacoubi Basma, Gabriel Dean W
Plant Molecular and Cell Biology Program, Plant Pathology Department, University of Florida, Gainesville, FL 32611, USA.
Mol Plant Microbe Interact. 2005 Dec;18(12):1306-17. doi: 10.1094/MPMI-18-1306.
Suppression subtractive hybridization (SSH) was used to identify genes present in the systemic crucifer black rot pathogen Xanthomonas campestris pv. campestris 528T but missing from the nonsystemic crucifer leaf spot pathogen, X. campestris pv. armoraciae 417. Among the DNA fragments unique to 528T was Xcc2109, one of eight putative avr genes identified in the published 528T genome (NC_003902). Individual and sequential deletion, insertion mutations, or both of all eight 528T avr gene loci were made, but no change in pathogenicity was observed with any combination of avr mutations, including a strain with all eight avr genes deleted. However, insertion or deletion mutants affecting the Xcc2109 locus lost avirulence (i.e., became virulent) on Florida Mustard, an X. campestris pv. campestris race-determining, differential host. The Xcc2109 open reading frame as annotated was cloned and found to be nonfunctional. A longer gene, encompassing Xcc2109 and here designated avrXccFM, was cloned and found to complement the Xcc2109 mutants and to confer avirulence to two additional wild-type X. campestris pv. campestris strains, thereby changing their races. Resistance in Florida Mustard to 528T strains carrying avrXccFM occurred without a typical hypersensitive response (HR) on leaves, although a vascular HR was observed in seedlings.
抑制性消减杂交（SSH）技术被用于鉴定存在于十字花科植物系统性黑腐病病原菌野油菜黄单胞菌野油菜致病变种528T中，但在非系统性十字花科叶斑病病原菌野油菜黄单胞菌萝卜致病变种417中缺失的基因。在528T特有的DNA片段中，有Xcc2109，它是在已公布的528T基因组（NC_003902）中鉴定出的8个假定avr基因之一。对所有8个528T的avr基因位点进行了单个或连续的缺失、插入突变，或两者兼而有之，但观察到任何avr突变组合都没有导致致病性的改变，包括一个所有8个avr基因都被删除的菌株。然而，影响Xcc2109位点的插入或缺失突变体在佛罗里达芥菜（一种野油菜黄单胞菌野油菜致病变种的小种鉴别寄主）上失去了无毒力（即变得有毒力）。克隆了注释的Xcc2109开放阅读框，发现其无功能。克隆了一个更长的基因，它包含Xcc2109，在这里命名为avrXccFM，发现它能互补Xcc2109突变体，并赋予另外两个野油菜黄单胞菌野油菜致病变种野生型菌株无毒力，从而改变它们的小种。佛罗里达芥菜对携带avrXccFM的528T菌株的抗性在叶片上没有典型的超敏反应（HR），尽管在幼苗中观察到了维管束HR。
