Cellular Responses of the Late Blight Pathogen Phytophthora infestans to Cyclic Lipopeptide Surfactants and Their Dependence on G Proteins

Oomycete pathogens cause major yield losses for many crop plants, and their control depends heavily on agrochemicals. Cyclic lipopeptides (CLPs) were recently discovered as a new class of natural compounds with strong activities against oomycetes. The CLP massetolide A (Mass A), produced by Pseudomo...

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Published in:Applied and Environmental Microbiology Vol. 75; no. 15; pp. 4950 - 4957
Main Authors: van de Mortel, Judith E, Tran, Ha, Govers, Francine, Raaijmakers, Jos M
Format: Journal Article
Language:English
Published: Washington, DC American Society for Microbiology 01-08-2009
American Society for Microbiology (ASM)
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Summary:Oomycete pathogens cause major yield losses for many crop plants, and their control depends heavily on agrochemicals. Cyclic lipopeptides (CLPs) were recently discovered as a new class of natural compounds with strong activities against oomycetes. The CLP massetolide A (Mass A), produced by Pseudomonas fluorescens, has zoosporicidal activity, induces systemic resistance, and reduces late blight in tomato. To gain further insight into the modes of action of CLPs, the effects of Mass A on pore formation, mycelial growth, sporangium formation, and zoospore behavior were investigated, as was the involvement of G proteins in the sensitivity of Phytophthora infestans to Mass A. The results showed that Mass A induced the formation of transmembrane pores with an estimated size of between 1.2 and 1.8 nm. Dose-response experiments revealed that zoospores were the most sensitive to Mass A, followed by mycelium and cysts. Mass A significantly reduced sporangium formation and caused increased branching and swelling of hyphae. At relatively low concentrations, Mass A induced encystment of zoospores. It had no effect on the chemotactic response of zoospores but did adversely affect zoospore autoaggregation. A loss-of-function transformant of P. infestans lacking the G-protein α subunit was more sensitive to Mass A, whereas a gain-of-function transformant required a higher Mass A concentration to interfere with zoospore aggregation. Results indicate that Mass A disturbs various developmental stages in the life cycle of P. infestans and suggest that the cellular responses of P. infestans to this CLP are, in part, dependent on G-protein signaling.
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J.E.V.D.M. and H.T. contributed equally to this work.
Corresponding author. Mailing address: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands. Phone: 31 317 483427. Fax: 31 317 483412. E-mail: jos.raaijmakers@wur.nl
ISSN:0099-2240
1098-5336
1098-6596
DOI:10.1128/AEM.00241-09