Signal transduction by Tga3, a novel G protein alpha subunit of Trichoderma atroviride.
Trichoderma species are used commercially as biocontrol agents against a number of phytopathogenic fungi due to their mycoparasitic characterisitics. The mycoparasitic response is induced when Trichoderma specifically recognizes the presence of the host fungus and transduces the host-derived signals to their respective regulatory targets. We made deletion mutants of the tga3 gene of Trichoderma atroviride, which encodes a novel G protein alpha subunit that belongs to subgroup III of fungal Galpha proteins. Deltatga3 mutants had changes in vegetative growth, conidiation, and conidial germination and reduced intracellular cyclic AMP levels. These mutants were avirulent in direct confrontation assays with Rhizoctonia solani or Botrytis cinerea, and mycoparasitism-related infection structures were not formed. When induced with colloidal chitin or N-acetylglucosamine in liquid culture, the mutants had reduced extracellular chitinase activity even though the chitinase-encoding genes ech42 and nag1 were transcribed at a significantly higher rate than they were in the wild type. Addition of exogenous cyclic AMP did not suppress the altered phenotype or restore mycoparasitic overgrowth, although it did restore the ability to produce the infection structures. Thus, T. atroviride Tga3 has a general role in vegetative growth and can alter mycoparasitism-related characteristics, such as infection structure formation and chitinase gene expression.
Zeilinger
Susanne
S
Research Area of Gene Technology and Applied Biochemistry, Institute for Chemical Engineering, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria. szeiling@mail.zserv.tuwien.ac.at
Reithner
Barbara
B
Scala
Valeria
V
Peissl
Isabel
I
Lorito
Matteo
M
Mach
Robert L
RL
D000118:Acetylglucosaminidase / Q000378:metabolism; D001483:Base Sequence; D002473:Cell Wall / Q000378:metabolism; D002688:Chitinases / Q000378:metabolism; D003001:Cloning, Molecular; D000242:Cyclic AMP / Q000378:metabolism; D004271:DNA, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005658:Fungi / Q000472:pathogenicity; D044385:GTP-Binding Protein alpha Subunits / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D009154:Mutation; D010572:Pest Control, Biological; D010641:Phenotype; D010944:Plants / Q000382:microbiology; D012232:Rhizoctonia / Q000472:pathogenicity; D015398:Signal Transduction; D014158:Transcription, Genetic; D014242:Trichoderma / Q000235:genetics / Q000378:metabolism*
D004271:DNA, Fungal; D005656:Fungal Proteins; D044385:GTP-Binding Protein alpha Subunits; D000242:Cyclic AMP; D002688:Chitinases; D000118:Acetylglucosaminidase