Genome-wide analysis of fatty acid desaturase (FAD) gene family in Camellia sinensis: Identification, expression and their biochemical functions in low temperature resistance

Fatty acid desaturase (FAD) is critical for unsaturated fatty acids (UFAs) biosynthesis and plays crucial roles in plants' response to low temperature. Nevertheless, a comprehensive genomic analysis of the FAD gene family in Camellia sinensis remain unreported. This study employed bioinformatics to identify 17 CsFAD genes, which are unequally distributed across 9 chromosomes. CsFAD proteins are localized to chloroplasts and/or endoplasmic reticulum (ER) by subcellular localization predictions. Phylogenetic categorization divides CsFADs into six subfamilies. The cis-elements are related to hormonal regulation and adversity response. Additionally, differential expression patterns of CsFADs across various tissues were observed. qRT-PCR analysis revealed a marked upregulation in the expression of CsSLD3 and CsSLD4 (encoding sphingolipid Delta 8 desaturase) under cold stress conditions. Moreover, subcellular localization assays in tobacco leaves confirmed the presence of CsSLD3 and CsSLD4 within ER. Yeast heterologous expression demonstrated the capacity of CsSLD3/4 to transform ceramide (t18:0) into ceramide(t18:1), and overexpression of CsSLD3/4 enhanced yeast tolerance to low temperature. Thus, this comprehensive analysis of the CsFAD gene family furnishes a robust foundation for future study into the biological functions of CsFAD genes, and offers a profound insight into their regulatory roles in stress resilience.