Tyler Brett M
Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
Annu Rev Phytopathol. 2002;40:137-67. doi: 10.1146/annurev.phyto.40.120601.125310. Epub 2002 Feb 20.
Recognition is the earliest step in any direct plant-microbe interaction. Recognition between Phytophthora pathogens, which are oomycetes, phylogenetically distinct from fungi, has been studied at two levels. Recognition of the host by the pathogen has focused on recognition of chemical, electrical, and physical features of plant roots by zoospores. Both host-specific factors such as isoflavones, and host-nonspecific factors such as amino acids, calcium, and electrical fields, influence zoospore taxis, encystment, cyst germination, and hyphal chemotropism in guiding the pathogen to potential infection sites. Recognition of the pathogen by the host defense machinery has been analyzed using biochemical and genetic approaches. Biochemical approaches have identified chemical elicitors of host defense responses, and in some cases, their cognate receptors from the host. Some elicitors, such as glucans and fatty acids, have broad host ranges, whereas others such as elicitins have narrow host ranges. Most elicitors identified appear to contribute primarily to basic or nonhost resistance. Genetic analysis has identified host resistance (R) genes and pathogen avirulence (Avr) genes that interact in a gene-for-gene manner. One Phytophthora Avr gene, Avr1b from P. sojae, has been cloned and characterized. It encodes a secreted elicitor that triggers a system-wide defense response in soybean plants carrying the cognate R gene, Rps1b.
识别是任何植物与微生物直接相互作用的最早步骤。疫霉菌病原体属于卵菌纲，在系统发育上与真菌不同，对其识别的研究主要集中在两个层面。病原体对宿主的识别主要关注游动孢子对植物根的化学、电和物理特征的识别。宿主特异性因子如异黄酮，以及宿主非特异性因子如氨基酸、钙和电场，都会影响游动孢子的趋化性、包囊形成、包囊萌发和菌丝向化性，引导病原体到达潜在的感染部位。宿主防御机制对病原体的识别已通过生化和遗传学方法进行了分析。生化方法已鉴定出宿主防御反应的化学激发子，在某些情况下，还鉴定出了宿主的同源受体。一些激发子，如葡聚糖和脂肪酸，具有广泛的宿主范围，而其他激发子，如激发素，则具有较窄的宿主范围。已鉴定出的大多数激发子似乎主要参与基础抗性或非寄主抗性。遗传学分析已鉴定出以基因对基因方式相互作用的宿主抗性（R）基因和病原体无毒（Avr）基因。一种疫霉菌的Avr基因，即来自大豆疫霉的Avr1b，已被克隆和鉴定。它编码一种分泌型激发子，能在携带同源R基因Rps1b的大豆植株中引发全系统的防御反应。
