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Functional analyses of heterotrimeric G protein G and Gβ subunits in Gibberella zeae

¹ School of Agricultural Biotechnology and Center for Agricultural Biomaterials, Seoul National University, Seoul 151-921, Republic of Korea
² Department of Pharmaceutical Engineering, Woosuk University, Wanju 565-701, Republic of Korea
³ Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843-2132, USA
⁴ Department of Medical Biotechnology, Soonchunhyang University, Asan 336-745, Republic of Korea

Correspondence
Yin-Won Lee
lee2443{at}snu.ac.kr

The homothallic ascomycete fungus Gibberella zeae (anamorph: Fusarium graminearum) is a major toxigenic plant pathogen that causes head blight disease on small-grain cereals. The fungus produces the mycotoxins deoxynivalenol (DON) and zearalenone (ZEA) in infected hosts, posing a threat to human and animal health. Despite its agricultural and toxicological importance, the molecular mechanisms underlying its growth, development and virulence remain largely unknown. To better understand such mechanisms, we studied the heterotrimeric G proteins of G. zeae, which are known to control crucial signalling pathways that regulate various cellular and developmental responses in fungi. Three putative G subunits, GzGPA1, GzGPA2 and GzGPA3, and one Gβ subunit, GzGPB1, were identified in the F. graminearum genome. Deletion of GzGPA1, a homologue of the Aspergillus nidulans G gene fadA, resulted in female sterility and enhanced DON and ZEA production, suggesting that GzGPA1 is required for normal sexual reproduction and repression of toxin biosynthesis. The production of DON and ZEA was also enhanced in the GzGPB1 mutant, suggesting that both G GzGPA1 and Gβ GzGPB1 negatively control mycotoxin production. Deletion of GzGPA2, which encodes a G protein similar to A. nidulans GanB, caused reduced pathogenicity and increased chitin accumulation in the cell wall, implying that GzGPA2 has multiple functions. Our study shows that G. zeae heterotrimeric G protein subunits can regulate vegetative growth, sexual development, toxin production and pathogenicity.