Background: Fusarium wilt disease of banana is one of the most devastating diseases and was responsible for destroying banana plantations in the late nineteenth century. Fusarium oxysporum f. sp. cubense is the causative agent. Presently, both race 1 and 4 strains of Foc are creating havoc in the major banana-growing regions of the world. There is an urgent need to devise strategies to control this disease; that is possible only after a thorough understanding of the molecular basis of this disease. Results: There are a few regulators of Foc pathogenicity which are triggered during this infection, among which Sge1 (Six Gene Expression 1) regulates the expression of effector genes. The protein sequence is conserved in both race 1 and 4 strains of Foc indicating that this gene is vital for pathogenesis. The deletion mutant, FocSge1 displayed poor conidial count, loss of hydrophobicity, reduced pigmentation, decrease in fusaric acid production and pathogenicity as compared to the wild-type and genetically complemented strain. Furthermore, the C-terminal domain of FocSge1 protein is crucial for its activity as deletion of this region results in a knockout-like phenotype. Conclusion: These results indicated that FocSge1 plays a critical role in normal growth and pathogenicity with the C-terminal domain being crucial for its activity.

Bidirectional promoters (BDPs) are regulatory DNA sequences (~1000 bp long) intervening two genes arranged on opposite strands with their 5′ ends in close proximity. these genes are mostly co-expressed; but, instances of anti-correlation and independent transcription have been observed. In fungal systems, BDPs have shown to provide an improved genetic circuit by assembling and regulating transcription of different genes of a common metabolic pathway. We have identified an intergenic region (1063 bp) from the genome of Fusarium oxysporum f. sp. cubense (Foc), a banana root pathogen. this intergenic region regulates the expression of a gene pair required for the breakdown of hemicellulose. For characterization, it was cloned into pCSN44 vector backbone between two reporter genes, namely β-glucuronidase (GUS) and enhanced green fluorescent protein (EGFP). The newly formed vector was transformed into Foc and tested for its bidirectional expression activity. Using histochemical staining and fluorescence microscopy, the kinetics for both, GUS and EGFP expression were tested under different growth conditions respectively. The activity was differentially regulated by inducers such as xylan, arabinogalactan and pectin. This is the first report on the isolation of the intergenic region with inducible bidirectional promoter activity from Fusarium. characterization of such BDPs will find applications in genetic engineering, metabolic engineering and synthetic biology using fungal systems.

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