Trichoderma atroviride G-protein alpha-subunit gene tga1 is involved in mycoparasitic coiling and conidiation.
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 (Galpha) gene (tgal) belonging to the fungal subfamily with the highest similarity to the Galpha1 class. Generated transgenic lines that overexpress Galpha 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 Tgal 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 Tgal 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.
Rocha-Ramirez
Víctor
V
Department of Plant Genetic Engineering, Centro de Investigación y Estudios Avanzados, Unidad Irapuato, 36500 Irapuato, Guanajuato, México.
Omero
Carmi
C
Chet
Ilan
I
Horwitz
Benjamin A
BA
Herrera-Estrella
Alfredo
A
D001483:Base Sequence; D000242:Cyclic AMP / Q000378:metabolism; D016373:DNA, Antisense / Q000235:genetics; D004271:DNA, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics; D005800:Genes, Fungal; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics*; D036341:Intercellular Signaling Peptides and Proteins; D037102:Lectins / Q000494:pharmacology; D008855:Microscopy, Electron, Scanning; D010455:Peptides / Q000494:pharmacology; D010572:Pest Control, Biological; D015398:Signal Transduction; D014242:Trichoderma / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity / Q000502:physiology; D014774:Virulence / Q000235:genetics
D016373:DNA, Antisense; D004271:DNA, Fungal; D005656:Fungal Proteins; D036341:Intercellular Signaling Peptides and Proteins; D037102:Lectins; C084070:Mas7 protein, synthetic; D010455:Peptides; D000242:Cyclic AMP; D020962:Heterotrimeric GTP-Binding Proteins