Age-Related Resistance of Nicotiana benthamiana Against Hemibiotrophic Pathogen Phytophthora infestans Requires Both Ethylene- and Salicylic Acid–Mediated Signaling Pathways

摘要

Phytophthora infestans , the agent of late blight disease of potato, is a hemibiotrophic pathogen with biotrophic action during early infection and necrotrophic in the later stage of colonization. Mature Nicotiana benthamiana was resistant to P. infestans , whereas relatively young plants were susceptible to this pathogen. Young plants became resistant following a pretreatment with acibenzolar- S -methyl, a functional analog of salicylic acid (SA), indicating that susceptibility of young plants is due to a lack of induction of SA signaling. Further analysis with virus-induced gene silencing indicated that NbICS1 and NbEIN2 , the genes for SA biosynthesis and ethylene (ET) signaling, respectively, are required for the resistance of mature N. benthamiana against P. infestans . Furthermore, these genes are required for the production of reactive oxygen species (ROS) induced by treatment of the INF1 elicitor. In NbICS1 -silenced plants, cell death induced by either INF1 or necrosis-inducing protein NPP1.1 was significantly accelerated. Expression of genes for phytoalexin (capsidiol) biosynthesis, NbEAS and NbEAH , were regulated by ET, and gene silencing of either of them compromised resistance of N. benthamiana to P. infestans . Together, these results suggest that resistance of N. benthamiana against hemibiotrophic P. infestans requires both SA-regulated appropriate induction of cell death and ET-induced production of phytoalexin.