Overexpression of plant defensins lead to increased tolerance to water stress in some of the grapevine populations

Plant defensin peptides are known for their role in biotic stress mitigation, but limited information is available for their roles in abiotic stress. Previous in silico analysis of transcriptomic data indicated the upregulation of Defensin-like (DEFL) genes in response to water deficit stress, while several abiotic stress responsive genes were co-expressed with the grapevine plant defensin, Vvi-AMP1. No functional characterisation data are however available for defensin peptides in grapevine in terms of drought resistance. In this study seven transgenic Vitis vinifera populations, overexpressing three plant defensin peptides (Hc-AFP1, Rs-AFP2 and Vvi-AMP1) in two grapevine cultivars (‘Sultana’ and ‘Red Globe’) were characterised to evaluate the defensins’ potential role in drought stress. The transgenic lines were subjected to active drying experiments and evaluated in terms of their intrinsic water use efficiency (iWUE). The results indicated that the specific cultivar (genotype) had a strong modulating influence in the behaviour of the different transgenic lines. The ‘Sultana’ populations overexpressing the Hc-AFP1 and Rs-AFP2 peptides, and the ‘Red Globe’ population overexpressing the Hc-AFP1 peptide all demonstrated increased iWUE under the induced drought stress conditions. In these lines, the overexpression of the peptides positively impacted on grapevine stomatal behaviour under water stress conditions, resulting in improved hydration status and improvement of the iWUE. These promising results provide scope to explore grapevine defensins for roles beyond the traditional biotic defence roles and point to more general stress responsive roles.