Leister R T, Ausubel F M, Katagiri F
Department of Biological Sciences, University of Maryland, Baltimore 21250, USA.
Proc Natl Acad Sci U S A. 1996 Dec 24;93(26):15497-502. doi: 10.1073/pnas.93.26.15497.
The Arabidopsis thaliana disease resistance genes RPS2 and RPM1 belong to a class of plant disease resistance genes that encode proteins that contain an N-terminal tripartite nucleotide binding site (NBS) and a C-terminal tandem array of leucine-rich repeats. RPS2 and RPM1 confer resistance to strains of the bacterial phytopathogen Pseudomonas syringae carrying the avirulence genes avrRpt2 and avrB, respectively. In these gene-for-gene relationships, it has been proposed that pathogen avirulence genes generate specific ligands that are recognized by cognate receptors encoded by the corresponding plant resistance genes. To test this hypothesis, it is crucial to know the site of the potential molecular recognition. Mutational analysis of RPS2 protein and in vitro translation/translocation studies indicated that RPS2 protein is localized in the plant cytoplasm. To determine whether avirulence gene products themselves are the ligands for resistance proteins, we expressed the avrRpt2 and avrB genes directly in plant cell using a novel quantitative transient expression assay, and found that expression of avrRpt2 and avrB elicited a resistance response in plants carrying the corresponding resistance genes. This observation indicates that no bacterial factors other than the avirulence gene products are required for the specific resistance response as long as the avirulence gene products are correctly localized. We propose that molecular recognition of P. syringae in RPS2- and RPM1-specified resistance occurs inside of plant cells.
拟南芥抗病基因RPS2和RPM1属于一类植物抗病基因，这类基因编码的蛋白质含有一个N端三联体核苷酸结合位点（NBS）和一个C端富含亮氨酸重复序列的串联阵列。RPS2和RPM1分别对携带无毒基因avrRpt2和avrB的细菌性植物病原体丁香假单胞菌菌株具有抗性。在这些基因对基因的关系中，有人提出病原体无毒基因产生特定的配体，这些配体被相应植物抗性基因编码的同源受体识别。为了验证这一假设，了解潜在分子识别的位点至关重要。对RPS2蛋白的突变分析以及体外翻译/转运研究表明，RPS2蛋白定位于植物细胞质中。为了确定无毒基因产物本身是否是抗性蛋白的配体，我们使用一种新型的定量瞬时表达测定法在植物细胞中直接表达avrRpt2和avrB基因，发现avrRpt2和avrB的表达在携带相应抗性基因的植物中引发了抗性反应。这一观察结果表明，只要无毒基因产物定位正确，除了无毒基因产物外，不需要其他细菌因子来引发特异性抗性反应。我们提出，在RPS2和RPM1介导的抗性中，对丁香假单胞菌的分子识别发生在植物细胞内部。
