Kiwifruit is an important fruit crop that is highly sensitive to environmental stresses, such as drought, heat, cold, water logging and phytopathogens. Therefore it is indispensable to identify stress-responsive candidate genes in kiwifruit cultivars for the stress resistance improvement. Here we report the isolation and characterization of a novel kiwifruit R1R2R3-MYB homolog (AcMYB3R) whose expression was induced by drought, salinity and cold stress. In vitro assays showed that AcMYB3R is a nuclear protein with transcriptional activation activity by binding to the cis-element of the kiwifruit orthologue of G2/M phase-specific gene KNOLLE. The Arabidopsis transgenic plants overexpressing AcMYB3R showed drastically enhanced tolerance to drought and salt stress. The expressions of stress-responsive genes such as RD29A, RD29B, COR15A and RD22 were prominently up-regulated by ectopic expression of AcMYB3R. Our study provides a valuable piece of information for functional genomics studies of kiwifruit and molecular breeding in improving stress tolerance for crop production.
