Preliminary Study On Fusarium Graminearum FgSWI6 Gene Which Is Involved In Cell Regulation And Virulence

Fusarium head blight (FHB) is a worldwide devastating disease of wheat, barley and other small grain cereals and caused primarily by Fusarium graminearum. Since the whole-genome sequencing project of F. graminearum was initiated by 2002, the research focus of this plant fungal pathogen has been transferred from the level of traditional plant pathology to the level of functional genomics and comparative genomics.In Saccharomyces cerevisiae, ScSWI6,ScSWI4 and ScMBP1 play very important roles in cell cycle regulations. SBF(Swi6p-Swi4p)and MBF(Mbp1p-Swi6p)complex can activate expression of a series of genes during the G1/S transition. Bioinformatic analysis reveals that there are two loci (FGSG₁0384.2 and FGSG₀4220.2) in the genome of F. graminearum, encoding hypothetical protein homologs for SBF/MBF components, respectively. The results of amino acid sequence alignment and domain/motif analysis indicate that the FGSG₀4220.2 encodes the hypothetical protein homolog for ScSwi6p, and we named FGSG₀4220.2 as FgSWI6 hereafter.Gene knock-out method was used to study the function of FgSWI6. We constructed the replacement vector and complementation vector for FgSWI6, and through PEG-CaCl2 mediated filamentous fungal transformation we obtained FgSWI6 gene deletion strain (fgswi6) and the complementation strain (fgswi6::FgSWI6) successfully. Morphological analysis revealed that:(1).Deletion of FgSWI6 reduces mycelial growth on solid-substrate surface,the growth rate of mycelium falls to 30% of that of the wild-type strain PH-1. However, this mycelial growth defect was not observed in liquid-medium culture.(2). F. graminearum cells lacking FgSWI6 show reduced production and development of conidia in F. graminearum , and also show reduced production efficiency and sizes of perithecia as well as a defect in the production of ascus and ascospore.(3).Deletion of FgSWI6 significantly attenuates the virulence of F. graminearum on wheat. The infection was limited to the inoculated spikelets and but not to the vascular bundle tissue of wheat.(4). Deletion of FgSWI6 causes mycelium growth become sensitive to MBC in liquid medium.In summary, we have characterized a hypothetical regulatory gene FgSWI6 in F. graminearum and revealed its functions in regulating cell growth, asexual and sexual development as well as virulence.The results of this study provide a basis for further studies on the pathogenicity mechanisms of F. graminearum and is useful for the development of new-type fungicides.