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Applied and Environmental Microbiology, August 2009, p. 4950-4957, Vol. 75, No. 15
0099-2240/09/$08.00+0     doi:10.1128/AEM.00241-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Cellular Responses of the Late Blight Pathogen Phytophthora infestans to Cyclic Lipopeptide Surfactants and Their Dependence on G Proteins{triangledown} ,{dagger}

Judith E. van de Mortel,1,{ddagger} Ha Tran,1,2,{ddagger} Francine Govers,1 and Jos M. Raaijmakers1*

Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1 6708 PB Wageningen, The Netherlands,1 Department of Plant Protection, Hue University of Agriculture and Forestry, Hue City, Vietnam2

Received 19 December 2008/ Accepted 29 May 2009

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 {alpha} 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.

* 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{at}wur.nl

{triangledown} Published ahead of print on 5 June 2009.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

{ddagger} J.E.V.D.M. and H.T. contributed equally to this work.

Applied and Environmental Microbiology, August 2009, p. 4950-4957, Vol. 75, No. 15
0099-2240/09/$08.00+0     doi:10.1128/AEM.00241-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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