Ong Laura E, Innes Roger W
Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Mol Microbiol. 2006 May;60(4):951-62. doi: 10.1111/j.1365-2958.2006.05162.x.
The Pseudomonas syringae pv. glycinea effector protein AvrB induces resistance responses in soybean varieties that contain the resistance gene Rpg1-b and Arabidopsis varieties that carry RPM1. In addition to this avirulence activity, AvrB also enhances bacterial virulence on soybean plants that lack Rpg1-b and induces a chlorotic phenotype on Arabidopsis plants that lack RPM1. We screened a library of avrB mutants for loss of avirulence on soybean and Arabidopsis, and assayed selected avirulence mutants for loss of virulence on both plants. All mutants screened were recognized similarly on both plant species. Nine single-site avrB mutations that affected avirulence localized to a solvent-accessible pocket in the protein structure. Seven of these mutated residues are absolutely conserved between AvrB and its nine homologues. Avirulence mutants generally lost virulence enhancement on susceptible soybean varieties and lost the ability to induce a chlorotic response on the rpm1 null Arabidopsis variety Mt-0. Three of four avirulence mutants tested failed to interact with RIN4, an Arabidopsis protein previously shown to be required for RPM1 function. Our results suggest that soybean and Arabidopsis recognize AvrB in the same manner, and that AvrB enzymatic activity is required for its function as an avirulence and virulence effector on two different plant species.
丁香假单胞菌大豆致病变种效应蛋白AvrB在含有抗性基因Rpg1-b的大豆品种和携带RPM1的拟南芥品种中诱导抗性反应。除了这种无毒活性外，AvrB还增强了对缺乏Rpg1-b的大豆植株的细菌致病性，并在缺乏RPM1的拟南芥植株上诱导出褪绿表型。我们筛选了一个avrB突变体文库，以寻找在大豆和拟南芥上无毒活性丧失的突变体，并检测所选无毒突变体在这两种植物上致病性的丧失情况。筛选出的所有突变体在这两种植物物种上的识别情况相似。影响无毒活性的9个avrB单位点突变定位于蛋白质结构中一个溶剂可及的口袋区域。其中7个突变残基在AvrB及其9个同源物之间是绝对保守的。无毒突变体通常在易感大豆品种上丧失了致病性增强能力，并且在rpm1缺失的拟南芥品种Mt-0上丧失了诱导褪绿反应的能力。测试的4个无毒突变体中有3个未能与RIN4相互作用，RIN4是一种拟南芥蛋白，先前已证明它是RPM1功能所必需的。我们的结果表明，大豆和拟南芥以相同的方式识别AvrB，并且AvrB的酶活性是其作为两种不同植物物种的无毒和致病效应子发挥功能所必需的。
