Downy mildew is a highly destructive disease in grapevine production. A gene encoding pathogenesis-related (PR) thaumatin-like protein was isolated from the downy mildew-resistant grapevine "Zuoshan-1," a clonal selection from wild Vitis amurensis Rupr. The predicted thaumatin-like protein (VaTLP) has 225 amino acids and it is acidic, with a calculated isoelectric point of 4.8. The full length of the VaTLP gene was transformed into somatic embryogenic calli of V. vinifera 'Thompson Seedless' via Agrobacterium tumefaciens. Real-time RT-PCR confirmed that the VaTLP gene was expressed at a high level in the transgenic grapevines. Improved resistance of the transgenic lines against downy mildew was evaluated using leaf disks and whole plants inoculated with Plasmopara viticola, the pathogen causing grapevine downy mildew disease. Bioassay of the pathogen showed that both hyphae growth and asexual reproduction were inhibited significantly among the transgenic plants. Histological analysis also confirmed this disease resistance by demonstrating the inhibition and malformation of hyphae development in leaf tissue of the transgenic plants. These results indicated that the accumulation of VaTLP could enhance resistance to P. viticola in transgenic 'Thompson Seedless' grapevines.
Keywords: Downy mildew; Grapevine; Resistance; Thaumatin-like protein; Transformation.