Glycosyltransferase-Like Toxin of Burkholderia gladioli Strain NGJ1 Is a Potent Antifungal Protein with Potential for Control of Sheath Blight Disease in Rice

Sheath blight disease caused by the fungal pathogen Rhizoctonia solani poses a great challenge for sustainable rice cultivation. It is important to develop environment-friendly measures for its control. Previously, a rice-associated Burkholderia gladioli strain NGJ1 has been shown to exhibit mycophagous and antifungal activity on R. solani. Here we report that a glucosyltransferase-like (BGT1) protein with a canonical DxD motif that is homologous to glycosyltransferase (GT) toxin of different bacteria is encoded in the antibacterial type VI secretion system (T6SS) encoding gene cluster of NGJ1. The recombinant BGT1 protein purified from Escherichia coli exhibits antifungal activity on R. solani, Magnaporthe oryzae, Fusarium oxysporum, Saccharomyces cerevisiae, and Candida albicans, under laboratory conditions. Using a variant of BGT1 protein (BGT1 D168L/D170L ), we demonstrate that DxD motif is important for its antifungal activity. The heterologous expression of native BGT1 but not BGT1 D168L/D170L protein prevents the growth of yeast cells. Moreover, treatment with BGT1 but not BGT1 D168L/D170L significantly reduces sheath blight disease severity in rice. BGT1 treatment does not elicit adverse effects on plants. In conclusion, we emphasize that BGT1 protein-based or transgene-based biotechnological interventions can be exploited for effective control of sheath blight disease in rice.