Studies on molecular mechanisms in the signal transduction cascade from signal perception to the expression of defense responsive genes in a plant-pathogen interaction

在本研究中，我们试图阐明感受真菌信号分子和防御反应基因表达之间的信号转导级联的分子机制。主要研究结果如下：1.豌豆质膜上的ATPase和多磷肌醇的代谢受寄主的克隆子和抑制子调控。然而，抑制子甚至在从真菌的非寄主植物分离的质膜中也能非特异性地阻止它们。松突根结线虫-激发子非特异性地增强豌豆和豌豆细胞壁中可溶于氯化钠的部分的ATPase(NTPase)、过氧化物酶和抗坏血酸氧化酶的活性，而抑制子则以种属特异性的方式抑制这些活性。激发子在豌豆细胞壁上产生的超氧阴离子和未知的侵染抑制物被抑制子抑制。另一方面，豌豆细胞壁中的那些基因被相反地诱导出…更多的是由抑制者独自完成的。导致植物保卫素产生的信号转导是通过细胞壁上的某些玻璃连结素样分子和质膜上的玻璃连结素样受体分子之间的连接来实现的。在PSPALs和PSCHSs的启动子序列中，我们发现了保守的序列基序，如Box-1(与Box L同源)、Box-2(与Box P同源)和Box-4(AT-box)，它们对激发子的应答是必不可少的。在PSCHSL中，直接重复的富含AT序列的TAAAATACT通过凝胶迁移率改变分析和体外DNase I足迹分析能够形成低迁移率复合体(LMC)。这一发现，即用碱性磷酸酶处理核因子可以消除LMC的形成，这表明核蛋白的磷酸化(S)是复杂机制形成所必需的。根据这些结果，我们提出了导致防御反应的信号转导途径如下：1)信号分子由细胞壁上的相应受体感知；2)第二信使通过质膜上的玻璃连素受体样蛋白进入细胞内；3)质膜上的多聚磷脂酰肌醇代谢也被激活以产生第三信使；4)信使刺激核因子的磷酸化(S)；5)防御反应基因的转录被激活；6)排斥反应在克隆子处理的植物组织中表达。较少

In this study, we attempted to clarify the molecular mechanisms in the signal transduction cascade between perception of fungal signal molecules and the expression of defense responsive genes.Our findings are summarized as follows :1. ATPase and polyphosphoinositide metabolism in pea plasma membranes are regulated by the clicitor and suppressor from Mycosphaerella pinodes. The suppressor, however, blocked nonspecifically them even in plasma membranes isolated from non-host plants of the fungus.2. The M.pinodes-elcitor enhanced nonspecifically the activities of ATPase (NTPase), peroxidase and ascorbic acid oxidase in NaCl-soluble fraction from cell walls isolated from pea and cowpea, whereas the suppressor blocked these activities in a species-specific manner.3. Superoxide anion and as yet unidentified infection-inhibitor, that were generated in isolated pea cell wall by the elicitor, were inhibited by the suppressor. On the other hand, those in cowpea cell wall were inversely elicited … More by the suppressor alone.4. Signal transduction leading to phytoalexin production was mediated by connection of certain vitronectin-like molecules in cell wall and vitronectin receptor-like molecules on plasma membrane.5. In the promoter sequence of PSPALs and PSCHSs, we found conserved sequence motifs, such as Box-1 (homologous to Box L), Box-2 (homologous to Box P) and Box-4 (AT-box) that were essential for response to the elicitor.6. In PSCHSL the directly repeated AT-rich sequences, TAAAATACT were capable of forming a low mobility complex (LMC) by a gel mobility shift assay and in vitro DNase i-footprinting analysis. The finding, that treatment of the nuclear factors with alkaline phosphatase abolished LMC formation, indicates phosphorylation of nuclear protein (s) is necessary for the formaiton of complex machinery.7. The cis-elements such as Box1, Box2 and G-box were essential for the promoter of elicitor-responsive CHS genes.From these results, we propose the stream of signal transduction leading to defense responses as follows : 1) signal molecules are percepted by respective receptors on cell wall ; 2) the second messengers are carried out into the cells via vitronectin receptor-like proteins on the plasma membranes ; 3) polyphosphoinositide metabolism in plasma membranes is also activated to produce the 3rd messenger ; 4) the messenger stimulates phosphorylation of nuclear factor (s) ; 5) The transcription of defense responsive genes are activated ; 6) the rejection reaction is expressed in the clicitor-treated plant tissues. Less