Takahashi Akira, Agrawal Ganesh Kumar, Yamazaki Muneo, Onosato Katsura, Miyao Akio, Kawasaki Tsutomu, Shimamoto Ko, Hirochika Hirohiko
Department of Molecular Genetics, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, Japan.
Plant Cell. 2007 Sep;19(9):2940-51. doi: 10.1105/tpc.106.047142. Epub 2007 Sep 21.
Tomato (Solanum lycopersicum) Pto encodes a protein kinase that confers resistance to bacterial speck disease. A second protein kinase, Pti1, physically interacts with Pto and is involved in Pto-mediated defense signaling. Pti1-related sequences are highly conserved among diverse plant species, including rice (Oryza sativa), but their functions are largely unknown. Here, we report the identification of a null mutant for the Pti1 homolog in rice and the functional characterization of Os Pti1a. The rice pti1a mutant was characterized by spontaneous necrotic lesions on leaves, which was accompanied by a series of defense responses and resistance against a compatible race of Magnaporthe grisea. Overexpression of Pti1a in rice reduced resistance against an incompatible race of the fungus recognized by a resistance (R) protein, Pish. Plants overexpressing Pti1a were also more susceptible to a compatible race of the bacterial pathogen Xanthomonas oryzae pv oryzae. These results suggest that Os Pti1a negatively regulates defense signaling for both R gene-mediated and basal resistance. We also demonstrated that repression of the rice RAR1 gene suppressed defense responses induced in the pti1a mutant, indicating that Pti1a negatively regulates RAR1-dependent defense responses. Expression of a tomato Pti1 cDNA in the rice pti1a mutant suppressed the mutant phenotypes. This contrasts strikingly with the previous finding that Sl Pti1 enhances Pto-mediated hypersensitive response (HR) induction when expressed in tobacco (Nicotiana tabacum), suggesting that the molecular switch controlling HR downstream of pathogen recognition has evolved differently in rice and tomato.
番茄（Solanum lycopersicum）的Pto编码一种蛋白激酶，赋予对细菌性斑点病的抗性。另一种蛋白激酶Pti1与Pto发生物理相互作用，并参与Pto介导的防御信号传导。Pti1相关序列在包括水稻（Oryza sativa）在内的多种植物物种中高度保守，但其功能大多未知。在此，我们报告了水稻中Pti1同源基因的一个无效突变体的鉴定以及Os Pti1a的功能表征。水稻pti1a突变体的特征是叶片上出现自发坏死病斑，同时伴有一系列防御反应以及对稻瘟病菌一个亲和小种的抗性。在水稻中过表达Pti1a降低了对由抗性（R）蛋白Pish识别的该真菌一个非亲和小种的抗性。过表达Pti1a的植株对水稻白叶枯病菌一个亲和小种也更敏感。这些结果表明，Os Pti1a对R基因介导的抗性和基础抗性的防御信号传导均起负调控作用。我们还证明，水稻RAR1基因的抑制抑制了pti1a突变体中诱导的防御反应，表明Pti1a对RAR1依赖性防御反应起负调控作用。在水稻pti1a突变体中表达番茄Pti1 cDNA可抑制突变体表型。这与之前的发现形成鲜明对比，即在烟草（Nicotiana tabacum）中表达时，Sl Pti1增强了Pto介导的过敏反应（HR）诱导，表明在水稻和番茄中，控制病原体识别下游HR的分子开关进化方式不同。
