Analysis of Molecular Basis for Gene-for-Gene Complementarity in Plant Diseases : Isolation of an Avirulence Gene from Phytophthora megasperma

点击翻译按钮获取中文摘要

Disease specificity in a particular combination between a given race and a plant cultivar is called as "race-cultivar specificity". This disease specificity is frequently controlled by gene-for-gene complementarity, in which resistance responses occur only when plant cultivars that express a dominant resistance gene are attacked by pathogen races that express a complementary a virulence gene. The interaction between soybean (Glycine max) and the fungal pathogen Phytophthora megasperma f.sp.glycinea is one of the best understood gene-for-gene plant-pathogen systems in which the processes leading to production of the phytoalexin glyceollin have been analyzed. Mycelial walls of the fungus have been shown to be potent elicitors of glyceollin accumulation, and their possible role in the induction of phytoalexin accumulation in infected plants has been suggested. However, neither specific elicitor explaining specificity between a soybean-cultivar and a race of P.megasperma nor avirulence gene of the fungus has been isolated. Thus, we have tried to isolate an avirulence gene of P.megasperma in this study. Unfortunately, we failed to achieve our final object : to isolate an avirulence gene from P.megasperma. However, we could reveal the existence of potential specific elicitor in intercellular fluid from P.megasperma rase1 infected soybean leaves (cv.Harosoy) to explain a specificity between the fungus and the plant. And also, we could show a structural model of how glucan elicitor is originally present in cell walls of P.megasperma and released by host beta-1,3-endoglucanase ; these data have been published in Plant Physiology (1995). Moreover, we could purify a glucan elicitor-binding protein from the membrane fraction of soybean root cells, and isolate its cDNA ; these data have been published in Proc.Natl.Acad.Sci.USA (1997, in press).