Allelic Variants, Genetic Effects, and Transcriptional Regulation of CoFAD7 in Camellia oleifera

Camellia oleifera Abel. is an important woody oil tree species in China, and increasing the content of polyunsaturated fatty acids (PUFAs), particularly α-linolenic acid (ALA), is critical for improving the quality of its oil. Fatty acid desaturase 7 (FAD7) is a key enzyme in ALA biosynthesis in plants. However, the allelic variation, functional role, and regulatory mechanisms underlying FAD7-mediated ALA accumulation in C. oleifera remain poorly understood. In the study, we cloned three homologous CoFAD7 genes: CoFAD7-1, CoFAD7-2, and CoFAD7-3 from C. oleifera 'Huashuo'. All three genes contained eight exons and seven introns, encoding 452 amino acids. Expression analysis revealed that CoFAD7 was highly expressed during the fruit maturation stage (258-333 DAP), correlating positively with seed ALA accumulation. Haplotypes analysis and transgenic experiments identified CoFAD7-G as a superior genotype associated with higher ALA content. Biochemical assays further showed that the transcription factor CoAP2-3 binds to the CoFAD7 promoter and activates its expression. These findings suggest that CoFAD7-G is a key determinant of ALA content, providing a theoretical basis for the early identification of high-ALA C. oleifera germplasm.