Kiwifruit (Actinidia chinensis) R1R2R3-MYB transcription factor AcMYB3R enhances drought and salinity tolerance in Arabidopsis thaliana

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.