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Applied and Environmental Microbiology, January 2004, p. 542-549, Vol. 70, No. 1
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.1.542-549.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Role of Two G-Protein Alpha Subunits, TgaA and TgaB, in the Antagonism of Plant Pathogens by Trichoderma virens

Prasun K. Mukherjee,1 Jagannathan Latha,1 Ruthi Hadar,2 and Benjamin A. Horwitz2*

Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Mumbai 400 085, India,1 Department of Biology, Technion—Israel Institute of Technology, Haifa 32000, Israel2

Received 22 May 2003/ Accepted 3 October 2003

G-protein {alpha} subunits are involved in transmission of signals for development, pathogenicity, and secondary metabolism in plant pathogenic and saprophytic fungi. We cloned two G-protein {alpha} subunit genes, tgaA and tgaB, from the biocontrol fungus Trichoderma virens. tgaA belongs to the fungal G{alpha}i class, while tgaB belongs to the class defined by gna-2 of Neurospora crassa. We compared loss-of-function mutants of tgaA and tgaB with the wild type for radial growth, conidiation, germination of conidia, the ability to overgrow colonies of Rhizoctonia solani and Sclerotium rolfsii in confrontation assays, and the ability to colonize the sclerotia of these pathogens in soil. Both mutants grew as well as the wild type, sporulated normally, did not sporulate in the dark, and responded to blue light by forming a conidial ring. The tgaA mutants germinated by straight unbranched germ tubes, while tgaB mutants, like the wild type, germinated by wavy and highly branched germ tubes. In confrontation assays, both tgaA and tgaB mutants and the wild type overgrew, coiled, and lysed the mycelia of R. solani, but tgaA mutants had reduced ability to colonize S. rolfsii colonies. In the soil plate assay, both mutants parasitized the sclerotia of R. solani, but tgaA mutants were unable to parasitize the sclerotia of S. rolfsii. Thus, tgaA is involved in antagonism against S. rolfsii, but neither G protein subunit is involved in antagonism against R. solani. T. virens, which has a wide host range, thus employs a G-protein pathway in a host-specific manner.

* Corresponding author. Mailing address: Department of Biology, Technion—Israel Institute of Technology, Haifa 32000, Israel. Phone: 972 4 8293976. Fax: 972 4 8225153. E-mail: horwitz{at}tx.technion.ac.il.

Applied and Environmental Microbiology, January 2004, p. 542-549, Vol. 70, No. 1
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.1.542-549.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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