Cellular responses of Phytophthora infestans to cyclic lipopeptide surfactants produced by Pseudomonas species

Oomycete pathogens cause devastating diseases on plants and animals and their control heavily depends on agrochemicals. With increasing concerns about adverse effects of agrochemicals on food safety and environment the development of novel, environmentally friendly control strategies, preferably based on natural products, is demanded. Cyclic lipopeptides (CLPs) produced by Pseudomonas species were discovered as a new class of natural compounds with strong activity against oomycetes including the late blight pathogen Phytophthora infestans. The Pseudomonas fluorescens CLP massetolide A (MassA), has zoosporicidal activity, induces systemic resistance and reduces late blight in tomato. To gain further insight in the modes of action of CLPs, effects on mycelial growth, sporangia formation, and zoospore behavior were investigated, as well as the involvement of G-proteins in sensitivity of P. infestans to MassA. In addition to zoospore lysis, MassA disturbed other developmental stages in the life cycle of P. infestans. G alpha gain-of-function mutants were less sensitive to MassA suggesting involvement of G-protein signaling in the response of P. infestans to this CLP. In order to reveal primary targets of CLPs we also monitored genome wide changes in gene expression. A distinct set of genes appeared to be up- or down-regulated after exposure to MassA, including genes encoding membrane transporters, alkaline phosphatases and pirins. Further characterization of these genes is in progress.