Recognition mechanism of flagellin which composed flagella of pathogenic bacteria and induction mechanism of resistance response in plnat.

燕麦假单胞菌（Acidovorax avenae）是一种革兰氏阴性细菌，其引起的幼苗疾病的特征是在受感染植物的鞘上形成棕色条纹。麦长管蚜在单子叶植物中的寄主范围很广，但单个菌株仅感染一种或几种寄主。我们发现，一个水稻不亲和株系，N1141，引起了抗性反应，如诱导过敏性细胞死亡和积累的EL 2或几丁质酶的mRNA，这被认为是防御相关基因，而水稻亲和株系，H8301，没有。基于这些结果，我们推测，这种诱导的抗性在水稻细胞介导的识别的一个特定的激发子分子所产生的不相容的菌株的P. avenae。为了鉴定特异性激发子，制备了针对N1141的菌株特异性抗体，然后用H8301细胞吸附。当通过SDS-PAGE分离菌株N1141的细胞提取物并用N1141菌株特异性抗体进行免疫染色时，仅检测到鞭毛蛋白。纯化的N1141鞭毛蛋白诱导培养的水稻细胞超敏性细胞死亡，而H8301鞭毛蛋白则不诱导。通过标记交换方法构建的鞭毛蛋白缺陷型N1141突变体完全丧失了过敏性细胞死亡的诱导能力和EL 2基因的表达能力，而鞭毛蛋白缺陷型相容菌株没有以与相容野生型相同的方式诱导这种抗性应答。这些结果表明，稻瘟病菌不亲和株系的鞭毛蛋白诱导了水稻细胞的抗病反应，而亲和株系的鞭毛蛋白则不诱导水稻细胞的抗病反应。另一方面，在N1141鞭毛蛋白缺陷突变体接种的水稻培养细胞中，Cht-1和PAL基因没有减少，这表明Cht-1基因的诱导受到另一条信号途径的调节。

Pseudomonas avenae (Acidovorax avenae) is a Gram-negative bacterium that causes a seedling disease characterized by the formation of brown stripes on the sheaths of infected plants. The host range of P.avenae is wide among monocotyledonous plants however, individual strains of the pathogen infect only one or a few host species. We shown that a rice-incompatible strain, N1141, caused a resistance response in cultured rice cells such as induction of the hypersensitive cell death and accumulation of EL2 or chitinase mRNAs which thought to be the defense-related gene, whereas a rice compatible strain, H8301, did not. Based on these results, we postulated that such induced resistance in rice cells is mediated by the recognition of a specific elicitor molecule produced by the incompatible strain of P.avenae. To identify the specific elicitor, a strain-specific antibody which was raised against N1141 and then absorbed with H8301 cells was prepared. When a cell extracts of strain N1141 was separated by SDS-PAGE and immunostained with the N1141 strain-specific antibody, only a flagellin protein was detected. Purified N1141 flagellin induced the hypersensitive cell death in cultured rice cells whereas the H8301 flagellin did not. A flagellin-deficient N1141 mutant constructed by marker exchange method completely lost the induction ability of hypersensitive cell death and the expression ability of the EL2 gene, whereas a flagellin-deficient compatible strain did not induce such resistance response in same manner as the compatible wild type. These results demonstrated that the resistance response in cultured rice cells is induced by the flagellin existing in the incompatible strain of P.avenae but not in the flagellin of the compatible strain. On the other hand, Cht-1 and PAL genes were not reduced in the N1141 flagellin-deficient mutant-inoculated cultured rice cells, suggesting that the induction of Cht-1 gene is regulated by another signal pathway.