CsFAD2 and CsFAD5 are key genes for C18:2 fatty acid pathway-mediated cold tolerance in tea (Camellia sinensis)

Low temperature is a limiting environmental factor that impairs the growth, yield and quality of tea plants. Fatty acids desaturations (FADs) play a key role in mediating membrane fluidity in response to various abiotic stresses; however, the intrinsic mechanisms underlying FAD-mediated alleviation of cold stress in tea plants are poorly understood. In this study, cold stress exposure significantly increased the content of C18:2 (linoleic acid) in two tea varieties contrasting in cold tolerance (cold-tolerant Longjin43 and cold-sensitive Huangjinye). Three different cDNA sequences, designated CsFAD2, CsFAD5 and CsFAD6, encoding ω-6 FADs that are involved in the response to cold stress were isolated from tea. Yeast experiments further demonstrated that CsFAD2, CsFAD5 and CsFAD6 can convert C18:1 to C18:2. Ectopic expression of CsFAD2, CsFAD5 and CsFAD6 in Arabidopsis seedlings and plants enhanced cold tolerance in pot experiments. Interestingly, CsFAD2-or CsFAD5-silenced tea leaves were more sensitive to cold acclimation than CsFAD6-silenced leaves, and CsFAD2/5-silenced leaves affected cold tolerance more than CsFAD2/6- or CsFAD5/6 -silenced leaves, suggesting that CsFAD2 and CsFAD5 were more important than CsFAD6 in cold acclimation-dependent cold tolerance. Taken together, our results suggest that C18:2 is an important component associated with cold stress and CsFAD2 and CsFAD5 contribute more than CsFAD6 to cold tolerance.