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United States Department of Agriculture

Agricultural Research Service

Research Project: FUNGAL RESOURCES FOR BIOLOGICAL CONTROL AND HIGH-VALUE USES

Location: Biological Integrated Pest Management Unit

Title: Hydrophobin genes of the entomopathogenic fungus, Metarhizium brunneum, are differentially expressed and corresponding mutants are decreased in virulence

Authors
item Sevim, A. -
item Donzelli, B.G.G. -
item Wu, D. -
item Demirbag, Z. -
item GIBSON, DONNA
item Turgeon, B. Gillian -

Submitted to: Current Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 4, 2012
Publication Date: March 3, 2012
Citation: Sevim, A., Donzelli, B., Wu, D., Demirbag, Z., Gibson, D.M., Turgeon, B. 2012. Hydrophobin genes of the entomopathogenic fungus, Metarhizium brunneum, are differentially expressed and corresponding mutants are decreased in virulence. Current Genetics. 58:79-92.

Interpretive Summary: Hydrophobins are a group of small peptides that appear to be important for fungal growth and development, although their functions have only been explored in relatively few fungi. We identified and characterized three different hydrophobin genes in Metarhizium brunneum, and produced mutants in which each gene had been deleted. These mutants showed alterations in expression patterns during development, and in pigmentation, spore production, morphology, and hydrophobicity, as well as a marked delay in virulence against two different insects. We show that these three hydrophobins have distinct, but compensating, roles in providing functionality for their producing organism.

Technical Abstract: Hydrophobins are small, cysteine-rich, secreted proteins, ubiquitously produced by filamentous fungi that are speculated to function in fungal growth, cell surface properties, and development, although this has been rigorously tested for only a few species. Herein, we report identification of three hydrophobin genes from the entomopathogenic fungus, Metarhizium brunneum and functional characterization of strains lacking these genes. One gene (HYD1/ssgA) encodes a Class I hydrophobin identified previously. Two new genes, HYD3 and HYD2, encode a Class-I and Class-II hydrophobin, respectively. To examine function, we deleted all three, separately, from the M. brunneum strain KTU-60 genome using Agrobacterium tumefaciens-mediated transformation. Deletion strains were screened for alterations in developmental phenotypes including growth, sporulation, pigmentation, colony surface properties, and virulence to insects. All deletion strains were reduced in their ability to sporulate and showed alterations in wild-type pigmentation, but all retained wild-type hydrophobicity, except for one individual hyd3 mutant. Complementation with the wild-type HYD3 gene restored hydrophobicity. Each gene, present as a single copy in the genome, showed differential expression patterns dependent on the developmental stage of the fungus. When Spodoptera exigua (beet armyworm) larvae were treated with either conidia or blastospores of each hyd mutant, reductions in pathogenicity and delayed mortality were observed as compared to WT. Together, these results suggest that hydrophobins are differentially expressed and may have distinct, but compensating roles, in conidiation, pigmentation, hydrophobicity, and pathogenicity.

Last Modified: 9/29/2014