番茄与叶霉菌互作的分子机理

 番茄和叶霉菌(Cladosporium fulvum Cooke)系统是研究植物和病原物互作分子机理的模式系统。4个叶霉菌无毒基因已被克隆。这些无毒基因编码含偶数个半胱氨酸的小分子量蛋白,在叶霉菌毒性菌株中的存在与否及存在方式各不相同。Avr4具有几丁质结合活性;而Avr9可能在叶霉菌氮素代谢中起调节作用。7个具有功能的番茄抗叶霉菌Cf基因已被克隆。它们与其同源基因一起以基因簇形式存在于复合基因座中,其成员称为Hcr (homologues of C. fulvum resistance gene Cf)基因。Cf蛋白定位于细胞质膜,但主体在膜外,主要结构域为富含亮氨酸重复(LRR)和跨膜结构域。LRR重复单元数目以及N端序列决定了Cf蛋白对Avr的识别特异性。Cf对Avr的识别遵守"保卫"假说。在Cf-2对Avr2的识别系统中,蛋白酶Rcr3为"被保卫"蛋白。Cf识别Avr后迅速激活下游信号传导和防卫反应,包括过敏性反应的产生和氧化迸发,以及K⁺离子通道、各类蛋白激酶、SGT1、硫氧还蛋白及磷脂酸途径的活化。温度、湿度和光照等环境条件显著影响Cf介导的过敏性反应和抗病性。不同Cf对Avr的识别机理及其下游信号传导途径有显著差别。

Molecular mechanism of interaction between tomato and leaf mold pathogen Cladosporium fulvum

The pathosystem of tomato and leaf mold fungal pathogen Cladosporium fulvum is a model system to study molecular mechanism of interaction between plant and pathogen.Four C.fulvum avirulence(Avr) genes have been cloned.All the Avr genes encode small molecular weight proteins with even numbers of cysteines,and their existence and variance are different in the virulent strains.Avr4 is of chitin-binding activity,while Avr9 might be involved in nitrogen regulation in the fungus.Seven functional tomato resistance(R) genes to C.fulvum have been cloned.They are clustered with nonfunctional homologues in complex loci and named as Hcr(homologues of C.fulvum resistance gene Cf) genes.The Cf proteins,which are anchored at plasma membrane with the main body outside,mainly consist of a leucine-rich repeat(LRR) and a transmembrane domain.Recognition of an Avr by the complementary Cf complies with the "guard" hypothesis.In re-(cognition) complex of Avr2 by Cf-2,the guarded protein is protease Rcr3.Avr recognition by a Cf rapidly eli-(cits) downstream signaling and defense responses,including occurrence of hypersensitive response(HR) and oxidative burst,activation of K~+ ion channel,a variety of protein kinases,SGT1,thioredoxin and phosphati-(dic) acid signaling pathway.Environmental conditions,including temperature,humidity and light,significantly affect Cf-dependent HR and resistance.Different Cf/Avr interactions might be distinct in Avr recognition and downstream signal transduction pathways.