A GENE ENCODING A PROTEIN ELICITOR OF PHYTOPHTHORA-INFESTANS IS DOWN-REGULATED DURING INFECTION OF POTATO

Most species of the genus Phytophthora produce 10-kDa extracellular pr otein elicitors, collectively termed elicitins. Elicitins induce hyper sensitive response in a restricted number of plants, particularly in t he genus Nicotiana within the Solanaceae family. A cDNA encoding INF1, the major secreted elicitin of Phytophthora infestans, a pathogen of solanaceous plants, was isolated and characterized. The expression of the corresponding inf1 gene during the disease cycle of P. infestans w as analyzed. inf1 was shown to be expressed in mycelium grown in vario us culture media, whereas it was not expressed in sporangiospores, zoo spores, cysts, and germinating cysts. In planta, during infection of p otato, particularly during the biotrophic stage, expression of inf1 wa s down-regulated compared to in vitro. The highest levels of expressio n of inf1 were observed in in vitro grown mycelium and in late stages of infection when profuse sporulation and leaf necrosis occur. The pot ential role of INF1 as an elicitor in interactions between I? infestan s and Solanum species was investigated. Nineteen lines, representing n ine solanaceous species with various levels of resistance to P. infest ans, were tested for response to an Escherichia coli expressed INF1. W ithin the genus Solanum, resistance to P. infestans did not appear to be mediated by a defense response elicited by INF1. However, INF1 reco gnition could be a component of nonhost resistance of tobacco to P. in festans.