Heterogeneous expression of stearoyl-acyl carrier protein desaturase genes SAD1 and SAD2 from Linum usitatissimum enhances seed oleic acid accumulation and seedling cold and drought tolerance capability in Brassica napus

Flax (Linum usitatissimum L.) as one of the versatile crops is a major source of unsaturated fatty acids in seeds. Stearoyl-acyl carrier protein desaturase (SAD) is a dehydrogenase enzyme that plays a key role in oleic acid biosynthesis as well as responses to biotic and abiotic stresses. However, the function of SAD orthologs from L. usitatissimum has not been assessed. Here, we found that two LuSAD genes, LuSAD1 and LuSAD2, are present in the genome of L. usitatissimum cultivar 'Longya 10'. Heterogeneous expression of either LuSAD1 or LuSAD2 in Arabidopsis thaliana resulted in the higher contents of total fatty acids and oleic acid in seeds. Interestingly, ectopic expression of LuSAD2 in A. thaliana caused altered plant architecture. Consistently, the overexpression of either LuSAD1 or LuSAD2 in Brassica napus also resulted in increased contents of total fatty acids and oleic acid in seeds. Furthermore, we demonstrated that either LuSAD1 or LuSAD2 enhances seedling resistance to cold and drought stresses via improving antioxidant enzyme activity and nonenzymatic antioxidant levels, as well as reducing membrane damage. These findings not only broaden our knowledge regarding the LuSAD functions in plants, but also offer promising targets for improving oil quantity and quality, and abiotic stress tolerance of oil-producing crops through molecular manipulation.