Mukherjee Prasun K, Latha Jagannathan, Hadar Ruthi, Horwitz Benjamin A
Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.
Appl Environ Microbiol. 2004 Jan;70(1):542-9. doi: 10.1128/AEM.70.1.542-549.2004.
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 Galphai 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.
G蛋白α亚基参与植物病原真菌和腐生真菌发育、致病性及次生代谢信号的传递。我们从生防真菌绿色木霉中克隆了两个G蛋白α亚基基因tgaA和tgaB。tgaA属于真菌Galphai类，而tgaB属于由粗糙脉孢菌gna - 2定义的类别。我们将tgaA和tgaB的功能缺失突变体与野生型在径向生长、产孢、分生孢子萌发、对峙试验中覆盖立枯丝核菌和齐整小核菌菌落的能力以及在土壤中定殖这些病原菌菌核的能力方面进行了比较。两个突变体与野生型生长情况相同，产孢正常，在黑暗中不产孢，且通过形成分生孢子环对蓝光作出反应。tgaA突变体通过直的无分支芽管萌发，而tgaB突变体像野生型一样通过波浪状且高度分支的芽管萌发。在对峙试验中，tgaA和tgaB突变体以及野生型都能覆盖、缠绕并裂解立枯丝核菌的菌丝体，但tgaA突变体定殖齐整小核菌菌落的能力有所降低。在土壤平板试验中，两个突变体都能寄生立枯丝核菌的菌核，但tgaA突变体无法寄生齐整小核菌的菌核。因此，tgaA参与了对齐整小核菌的拮抗作用，但两个G蛋白亚基均不参与对立枯丝核菌的拮抗作用。具有广泛宿主范围的绿色木霉因此以宿主特异性方式利用G蛋白途径。
