Transgenic tobacco and tomato plants expressing Wasabi defensin genes driven by root-specific LjNRT2 and AtNRT2.1 promoters confer resistance against Fusarium oxysporum

Antifungal peptides are a potential group of defense molecules that have been utilized to develop resistance to various plant pathogens. Wasabi defensin (WD) gene (0.5 kb) consists of cysteine-rich peptides that show potent growth inhibition of pathogenic filamentous fungi, such as Botrytis cinerea. Under regulation by the root-specific LjNRT2 or AtNRT2.1 promoter, WD gene was expressed in the roots of transgenic tobacco and tomato plants by Agrobacterium-mediated transformation. The regenerated plants showed stable integration of the transgene, with different insertion sites, and the transgene was expressed in the root tissues but not in the leaf tissues. This result confirmed that WD protein accumulated only in the roots of transgenic plants. In a bioassay for resistance to Fusarium oxysporum, all transgenic plants showed increased resistance to the fungus as compared to non-transformed plants. Protein extracts from root and leaf tissues were assayed for antifungal activity and the activity was express as the number of colonies formed per cm(2) (CFU cm(-2)). The CFU values of the root and leaf extracts of control plants did not show significant differences. In contrast, the CFU values of the root extracts of the transgenic plants were significantly lower than those of the leaf extracts and much lower than those of control. These results suggest that LjNRT2 and AtNRT2.1 promoters triggered the antifungal gene expression in the roots and conferred increased resistance to the root pathogen F. oxysporum. In the view of bio-safety, the root-specific expression of the transgene is desirable because the roots of tomato are not edible.