Strawberry FaNAC2 Enhances Tolerance to Abiotic Stress by Regulating Proline Metabolism

The quality and yields of strawberry plants are seriously affected by abiotic stress every year. NAC (NAM, ATAF, CUC) transcription factors are plant-specific, having various functions in plant development and response to stress. In our study, FaNAC2 from strawberry (Fragaria x ananassa, cultivar "Benihoppe") was isolated and found to be a member of the ATAF sub-family, belonging to the NAC family of transcription factors. FaNAC2 was strongly expressed in the shoot apical meristem and older leaves of strawberries, and was induced by cold, high salinity, and drought stress. To investigate how FaNAC2 functions in plant responses to abiotic stress, transgenic Nicotiana benthamiana plants ectopically overexpressing FaNAC2 were generated. The transgenic plants grew better under salt and cold stress, and, during simulated drought treatment, these transgenic lines not only grew better, but also showed higher seed germination rates than wild-type plants. Gene expression analysis revealed that key genes in proline biosynthesis pathways were up-regulated in FaNAC2 overexpression lines, while its catabolic pathway genes were down-regulated and proline was accumulated more with the overexpression of FaNAC2 after stress treatments. Furthermore, the gene expression of abscisic acid biosynthesis was also promoted. Our results demonstrate that FaNAC2 plays an important positive role in response to different abiotic stresses and may be further utilized to improve the stress tolerance of strawberry plants.