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Microbiology 153 (2007), 2850-2861; DOI  10.1099/mic.0.2007/007708-0
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Microbiology 153 (2007), 2850-2861; DOI  10.1099/mic.0.2007/007708-0
© 2007 Society for General Microbiology

Fusarium verticillioides GAP1, a gene encoding a putative glycolipid-anchored surface protein, participates in conidiation and cell wall structure but not virulence

Uma Shankar Sagaram, Brian D. Shaw and Won-Bo Shim

Department of Plant Pathology and Microbiology, Program for the Biology of Filamentous Fungi, Texas A&M University, College Station, TX 77843-2132, USA

Correspondence
Won-Bo Shim
wbshim{at}tamu.edu

Fusarium verticillioides is an important pathogen of maize that causes ear rot and produces the mycotoxins known as fumonisins. To date, knowledge of pathogenicity and the regulation of fumonisin biosynthesis in F. verticillioides is limited. Here, the molecular characterization of GAP1, a gene encoding a putative 540 aa protein that belongs to a glycolipid-anchored surface (GAS) protein family, is presented. F. verticillioides GAP1 was identified as an expressed sequence tag (EST) upregulated in a culture condition conducive to conidiation and fumonisin B1 (FB1) production. GAP1 null mutants GAM126 ({Delta}gap1 : : HYG) and GAG8 ({Delta}gap1 : : GEN) exhibited restricted growth, with more aerial hyphae than their wild-type progenitor on solid media. No defect in mycelial mass or filamentous growth was observed when the GAM126 and GAG8 strains were grown in liquid media under shaking conditions. When grown in suspended conditions, GAM126 and GAG8 strains produced significantly fewer conidia and produced comparatively densely branched hyphae. Concanavalin A staining indicated that the GAP1 deletion altered the cell wall carbohydrate composition/deposition process. Deletion of GAP1 did not affect the production level of FB1 or F. verticillioides virulence on maize seedlings and stalks. Complementation of GAM126 with the wild-type GAP1 gene restored growth, conidiation and cell wall abnormality phenotypes. The results suggest that GAP1 is associated with growth, development and conidiation in F. verticillioides, but not with pathogenicity or regulation of FB1.

Abbreviations: CFW, Calcofluor white; ConA, concanavalin A; CR, Congo red; EST, expressed sequence tag; FB1, fumonisin B1; GAS protein, glycolipid-anchored surface protein; GPI, glycosylphosphatidylinositol; SSH, suppression subtractive hybridization

The GenBank/EMBL/DDBJ accession no. for the 350 bp GAP1 gene sequence from F. verticillioides is DQ458798.

Figures showing the F. verticillioides seedling rot assay on hybrid sweetcorn, and Northern analysis of GAP2 and GAP3 expression in F. verticillioides, are available as supplementary data with the online version of this paper.






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