Whole‐Genome Identification of the Flax Fatty Acid Desaturase Gene Family and Functional Analysis of the LuFAD2 . 1 Gene Under Cold Stress Conditions

Fatty acid desaturase (FAD) is essential for plant growth and development and plant defence response. Although flax ( Linum usitatissimum L.) is an important oil and fibre crop, but its FAD gene remains understudied. This study identified 43 LuFAD genes in the flax genome. The phylogenetic analysis divided the FAD genes into seven subfamilies. LuFAD is unevenly distributed on 15 chromosomes, and fragment duplication is the only driving force for the amplification of the LuFAD gene family. In the LuFAD gene promoter region, most elements respond to plant hormones (MeJA, ABA) and abiotic stresses (anaerobic and low temperature). The expression pattern analysis showed that the temporal and spatial expression patterns of all LuFAD genes in different tissues and the response patterns to abiotic stresses (heat and salt) were identified. Subcellular localisation showed that all LuFAD2 ‐GFP were expressed in the endoplasmic reticulum membrane. RT‐qPCR analysis revealed that LuFAD2 was significantly upregulated under cold, salt and drought stress, and its overexpression in Arabidopsis thaliana enhanced cold tolerance genes and reduced ROS accumulation. This study offers key insights into the FAD gene family's role in flax development and stress adaptation. Flax is a vital oil and fibre crop, yet the FAD gene family is underexplored. In this study, we identified 43 LuFAD genes in the flax genome, with all FAD2 genes confirmed to be expressed in the endoplasmic reticulum. Notably, LuFAD2.1 overexpression enhances cold tolerance by promoting desaturation and reactive oxygen species (ROS) clearance. These findings advance our understanding of fatty acid desaturation in flaxseed and provide a foundation for improving crop performance and stress resilience.