A Xanthomonas transcription activator-like effector is trapped in nonhost plants for immunity

Xanthomonas oryzae pv.oryzae(Xoo),the causal agent of bacterial leaf blight in rice,delivers transcription activator-like effector(TALE)proteins into host cells to activate susceptibility or resistance(R)genes that promote disease or immunity,respectively.Nonhost plants serve as potential reservoirs of R genes;consequently,nonhost R genes may trap TALEs to trigger an immune response.In this study,we screened 17 Xoo TALEs for their ability to induce a hypersensitive response(HR)in the nonhost plant Nicotiana benthamiana(Nb);only AvrXa10 elicited an HR when transiently expressed in Nb.The HR generated by AvrXa10 required both the central repeat region and the activation domain,suggesting a specific interaction between AvrXa10 and a potential R-like gene in nonhost plants.Evans blue staining and ion leakage measurements confirmed that the AvrXa10-triggered HR was a form of cell death,and the transient expression of AvrXa10 in Nb induced immune responses.Genes targeted by AvrXa10 in the Nb genome were identified by transcriptome profiling and prediction of effector binding sites.Using several approaches(in vivo reporter assays,electrophoretic mobility-shift assays,targeted designer TALEs,and on-spot gene silencing),we confirmed that AvrXa10 targets NbZnFP1,a C2H2-type zinc finger protein that resides in the nucleus.Functional analysis indicated that overexpression of NbZnFP1 and its rice orthologs triggered cell death in rice protoplasts.An NbZnFP1 ortholog was also identified in tomato and was specifically activated by AvrXa10.These results demonstrate that NbZnFP1 is a nonhost R gene that traps AvrXa10 to promote plant immunity in Nb.

4种金龟甲的寄主偏好性及对不同植物挥发物的EAG反应

为了揭示华北大黑鳃金龟、暗黑鳃金龟、小黄鳃金龟和福婆鳃金龟对不同植物的寄主偏好性,本研究调查了四种金龟甲在6种寄主植物桃树、梨树、榆树、山楂、丁香和金银木上的发生情况。同时采用动态顶空吸附法收集7种植物挥发物,利用触角电位EAG技术,测定四种金龟甲雌、雄虫对不同寄主植物玉兰、柿树、金银木、榆树、芙蓉葵、丁香及非寄主植物银杏的挥发物的EAG反应。结果显示,金龟甲对不同寄主植物的偏好性有显著差异,华北大黑鳃金龟的偏好寄主为梨树,暗黑鳃金龟的偏好寄主为榆树、山楂和梨树,而小黄鳃金龟和福婆鳃金龟的偏好寄主均为丁香。四种金龟甲均对其共同寄主植物榆树挥发物的EAG反应最大,另外,小黄鳃金龟和福婆鳃金龟对丁香挥发物也有较大的EAG反应。对同一植物挥发物,华北大黑鳃金龟雌虫对部分植物挥发物的EAG反应比雄虫大;而其它3种鳃金龟雌、雄虫对所测试的植物挥发物的EAG反应均无显著性差异。上述结果说明金龟甲EAG反应的大小与其寄主偏好性一致。

植物免疫系统研究进展

在植物的生长环境中,存在大量的微生物。微生物对植物的影响可以是通过互利共生起促进作用,也可能起抑制作用而妨碍植物的健康生长,后者就是植物的病原菌。植物利用两类内在免疫系统对病原菌的侵染产生防卫反应,第一类免疫系统被称为微生物相关分子模式启动的免疫反应,对许多种微生物的常见分子识别并产生反应;第二类免疫系统被称为激活物启动的免疫反应,对病原菌毒性因子产生反应,这些毒性因子直接或间接通过对寄主目标起作用。对植物免疫功能及其机理的深入了解,为作物遗传改良和大面积生产中病害综合防治提供依据。