ABSTRACT
ω-3-Fatty acid desaturase 8 (FAD8), as a dehydrogenase enzyme, plays a key role in the transformation of saturated fatty acids into unsaturated fatty acids, which is helpful to enhance the freezing tolerance of plants. However, it remains unclear whether the expression level of FAD8 in Perilla frutescens is regulated by low temperature. Based on transcriptome data, the FAD8 gene was cloned, characterized and then successfully expressed in tobacco Nicotiana tabacum. The gene was designated as PfFAD8 and has a full-length coding sequence of 1 317 bp coding for 438 amino acids with a predicted molecular weight of 50 kD and a theoretical isoelectric point of 9. 13. Our research indicated that the expression of PfFAD8 in Perilla frutescens was increased under the freezing stress. To further confirm this result, a 35S::PfFAD8 vector were constructed and transformed into N. tabacum by Agrobacterium tumefaciens-mediated transformation. Transgenic tobacco leaves that over-expressed the PfFAD8 gene exhibited significantly higher unsaturated fatty acids (UFA) such as linoleic (C18:2) and palmitic acid (C16:0) content and advanced freezing tolerance. Moreover, PfFAD8 overexpression in transgenic tobacco leaves increases malondialdehyde (MDA) and proline (PRO) content, and enhances defense enzymes activities of superoxide dismutase (SOD) and catalase (CAT) to some extent under the cold condition, which might prevent the decline of UFA. Taken together, PfFAD8 overexpression in Perilla frutescens might be involved in the desaturation process of lipids leading to increased membrane stability and/ or induction of other genes related to freezing tolerance by octadecanoid pathway or lipid peroxidation products. Thus, PfFAD8 overexpression could be useful in the production of freeze-tolerant varieties of N. tabacum.