植物天然免疫性研究进展及其对作物抗病育种的可能影响

Recent Findings in Plant Innate Immunity and Possible Impacts on Crop Disease-resistance Breeding

植物定植在充满各种病原菌的环境中却能健康生长,显示其拥有一套免疫系统以应对病原物的侵染。最近,人们发现植物免疫系统至少包括2个层次:第一层为病原相关分子模式(PAMP)激发的免疫性(PTI),即植物通过细胞表面模式识别受体(PRRs)对病原菌的PAMPs进行分子识别,从而启动植物的防卫反应;第二层为病原菌效应子激发的免疫性(ETI),即有些毒性强的病原菌通过产生效应子(effectors)来抑制PTI,从而突破植物的第一道防线,而植物又进化出新的分子受体(例如R基因编码的NBS-LRR蛋白质)以侦察病原菌效应子并启动第二道防卫反应。数亿年来,病原菌的侵染和植物的防卫交替进行,促进了病原菌和植物基因组的共进化。最新的研究还发现,黄单胞杆菌TAL effectors和寄主植物DNA的相互识别中,利用了精准的分子密码。TAL effector类蛋白识别植物靶基因的启动子序列,识别模式是2个氨基酸识别一个核苷酸。通过这种识别,TAL effector操控植物靶基因的表达,引起寄主植物的感病或抗病反应。上述抗病分子机制研究的突破,将对植物抗病育种产生重要影响。

Plants have been successfully living in such an environment in which there are myriads of potential microbial pathogens,indicating that plants possess an efficient immunity system.Recent studies have revealed that the plant immunity system consists of two layers of defense.The first layer,based on the sensitive perception of pathogen-associated molecular patterns （PAMPs） through pattern recognition receptors （PRRs） at the plant cell surface,is named as PAMP-triggered immunity （PTI）.The second is called effector-triggered immunity （ETI）,in which plants use additional receptors （such as R-gene products） to perceive pathogen virulence effectors that have evolved to suppress PTI.The conventional gene-for-gene resistance in plants belongs actually to ETI.For millions of years,natural selection has been driving pathogens to avoid ETI either by diversifying the recognized effectors or by acquiring additional effectors that suppress ETI.On the other hand,natural selection favors plant new R-genes that can recognize the newly acquired effectors in pathogen,resulting in new ETI to be triggered again.The latest studies have revealed the simple cipher that governs DNA recognition by TAL （transcription activator-like） effectors from plant pathogenic Xanthomonas.TAL effectors can specifically bind the target DNA of host plant with a novel protein-DNA binding pattern in which two amino acids recognize one nucleotide.Using this recognition code,TAL effectors can bind the promoter of target genes and induce the host diseases or resistance responses.Recent findings about plant innate immunity are reviewed in this paper and their possible applications in plant breeding for disease resistance are discussed.