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Eukaryotic Cell, August 2002, p. 594-605, Vol. 1, No. 4
1535-9778/02/$04.00+0     DOI: 10.1128/EC.1.4.594-605.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Trichoderma atroviride G-Protein {alpha}-Subunit Gene tga1 Is Involved in Mycoparasitic Coiling and Conidiation

Víctor Rocha-Ramírez,1 Carmi Omero,2 Ilan Chet,2 Benjamin A. Horwitz,3 and Alfredo Herrera-Estrella1*

Department of Plant Genetic Engineering, Centro de Investigación y Estudios Avanzados, Unidad Irapuato, 36500 Irapuato, Guanajuato, México,1 Otto Warburg Center for Agricultural Biotechnology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot 76100,2 Department of Biology, Technion—Israel Institute of Technology, Haifa 32000, Israel3

Received 23 January 2002/ Accepted 15 May 2002

The soil fungus Trichoderma atroviride, a mycoparasite, responds to a number of external stimuli. In the presence of a fungal host, T. atroviride produces hydrolytic enzymes and coils around the host hyphae. In response to light or nutrient depletion, asexual sporulation is induced. In a biomimetic assay, different lectins induce coiling around nylon fibers; coiling in the absence of lectins can be induced by applying cyclic AMP (cAMP) or the heterotrimeric G-protein activator mastoparan. We isolated a T. atroviride G-protein {alpha}-subunit (G{alpha}) gene (tga1) belonging to the fungal subfamily with the highest similarity to the G{alpha}i class. Generated transgenic lines that overexpress G{alpha} show very delayed sporulation and coil at a higher frequency. Furthermore, transgenic lines that express an activated mutant protein with no GTPase activity do not sporulate and coil at a higher frequency. Lines that express an antisense version of the gene are hypersporulating and coil at a much lower frequency in the biomimetic assay. The loss of Tga1 in these mutants correlates with the loss of GTPase activity stimulated by the peptide toxin Mas-7. The application of Mas-7 to growing mycelial colonies raises intracellular cAMP levels, suggesting that Tga1 can activate adenylyl cyclase. In contrast, cAMP levels and cAMP-dependent protein kinase activity drop when diffusible host signals are encountered and the mycoparasitism-related genes ech42 and prb1 are highly expressed. Mycoparasitic signaling is unlikely to be a linear pathway from host signals to increased cAMP levels. Our results demonstrate that the product of the tga1 gene is involved in both coiling and conidiation.

* Corresponding author. Mailing address: Centro de Investigación y Estudios Avanzados, Unidad Irapuato, A.P. 629, 36500 Irapuato, Guanajuato, Mexico. Phone: 52/462/6239600. Fax: 52/462/6245849. E-mail: aherrera{at}ira.cinvestav.mx.

Eukaryotic Cell, August 2002, p. 594-605, Vol. 1, No. 4
1535-9778/02/$04.00+0     DOI: 10.1128/EC.1.4.594-605.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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