Functional Characterization Of Fusarium Graminearum PTC1 Gene

Fusarium graminearum is the major causal agent of Fusarium head blast (FHB) disease on wheat, which causes yield loss and affects the quality of grains. Mycotoxin produced by this fungus largely affects the safety for human food and animal feed, so FHB is a plant disease of great importance in agriculture. Since 1990s, the increased frequency of FHB outbreak has occurred in China and other major wheat-producing countries. On the other side, the extensive use of chemical fungicides such as carbendazols has caused the drug resistance of the pathogen in some parts of China. The continuous use of fungicides may increase the potential risk of FHB outbreak. Recent studies on F. graminearum have been focused on the pathogenesis and the discovery of drug targets.Due to the accomplishment of the genomic sequence of F. graminearum, the large-scale study of functional genes is underway. We initiate the functional genomic research by studying the functions of key regulatory genes in important signaling pathways. The aim is to discover the roles of these regulatory genes in fungal growth, development, interaction between the pathogen and the host, and pathogenesis. In the eukaryotic model organism Saccharomyces cerevisiae, ScPTC1 encodes a type 2C protein serine/threonine phosphatase. ScPtc1p is a negative regulator of the high osmolarity and glycerol (HOG) pathway. It is known that HOG pathway is involved in the formation of hyphae in fungi. Through the forward genetic approach, we identified the sequence homologue of ScPTC1 in the genome of F. graminearum, FgPTC1. FgPTC1 gene contains one single intron and has an open reading frame (ORF) of 1743 bp. In this study, we constructed the knockout cassette for the FgPTC1 gene and successfully deleted the ORF of FgPTC1 gene by homologous recombination. We have found that cells deleted for FgPTC1 are sensitive to lithium and grow slower in comparison to the wild-type cells.This study also exploits the possible complementary function of the FgPTC1 gene in S. cerevisiae. We cloned the cDNA sequence of the FgPTC1 gene into a yeast expression vector with a constitutive promoter of yeast ADH1, the alcohol dehydrogenase gene. As a result, we have found that the FgPTC1 cDNA sequence could complement the function of ScPTC1 in lithium tolerance, which indicates that the FgPTC1 and ScPTC1 genes are functional homologues. This study provides a basis for further studies on the role of the HOG pathway in the growth, development and virulence of Fusarium graminearum.