RdreB1BI Gene Expression Driven by the Stress-Induced Promoter rd29A Enhances Tolerance to Cold Stress in Benihope Strawberry

To develop a new germplasm of strawberry with tolerance to cold stress, we introduced the RdreB1BI gene driven by the stress promoter rd29A via agrobacterium-mediated transformation into the strawberry cultivar 'Benihope'. Five transgenic plants were examined with GUS, PCR and RT-PCR, and the copy number of the target gene was determined using inverse PCR methods. The results showed that the RdreB1BI gene had been integrated into the genome of the 'Benihope' strawberry, and the copy number ranged from one to three. To test the tolerance to cold stress in the five strains, a cold stress test was performed. The line with one copy of the target gene could tolerate -4 degrees C cold stress and was selected for further determination of the malondialdehyde index (MDA), the content of proline, soluble protein and soluble sugar, as well as the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT). The genetic line with the introduced RdreB1BI gene demonstrated significantly reduced MDA accumulation, increased content of soluble protein, soluble sugar and free proline and increased SOD and CAT activity. These findings suggest that the introduction of one copy of the target gene can improve tolerance to cold stress. The physiological index demonstrated that the RdreB1BI gene enhanced the tolerance to cold stress in strawberry through increasing the content of soluble protein, soluble sugar and free proline and enhancing the activity of SOD and CAT. This is the first report on the development of a new strawberry cultivar through the introduction of a transcription factor driven by a stress promoter in a commercial cultivar to enhance to expression of a desirable trait.