The structural basis for activation of plant immunity by bacterial effector protein AvrPto

摘要

Pathogenic microbes use effectors to enhance susceptibility in host plants. However, plants have evolved a sophisticated immune system to detect these effectors using cognate disease resistance proteins, a recognition that is highly specific, often elicits rapid and localized cell death, known as a hypersensitive response, and thus potentially limits pathogen growth. Despite numerous genetic and biochemical studies on the interactions between pathogen effector proteins and plant resistance proteins, the structural bases for such interactions remain elusive. The direct interaction between the tomato protein kinase Pto and the Pseudomonas syringae effector protein AvrPto is known to trigger disease resistance and programmed cell death through the nucleotide-binding site/leucine-rich repeat (NBS-LRR) class of disease resistance protein Prf. Here we present the crystal structure of an AvrPto-Pto complex. Contrary to the widely held hypothesis that AvrPto activates Pto kinase activity, our structural and biochemical analyses demonstrated that AvrPto is an inhibitor of Pto kinase in vitro. The AvrPto-Pto interaction is mediated by the phosphorylation-stabilized P+l loop and a second loop in Pto, both of which negatively regulate the Prf-mediated defences in the absence of AvrPto in tomato plants. Together, our results show that AvrPto derepresses host defences by interacting with the two defence-inhibition loops of Pto.%很多微生物植物病原体都形成了促动蛋白(effector proteins)，它们通 过中和宿主植物的防卫系统来增强毒性。针对这种情况，植物也形成 了具有高度特异性的抗性蛋白，它们能识别出促动蛋白，限制其感染 蜒经常是通过诱导局部化的细胞死亡来发挥这种作用的。现在，研究 人员已经确定了这些促动蛋白中其中一个的晶体结构，它就是来自 Pseudomonas syringiae的AvrPto，与Pto激酶结合在一起，后者能够 让番茄产生对细菌性斑点病的抵抗力。它们之间相互作用的性质表明， Pro可能是作为AvrPto毒性目标的一个模仿物而形成的。