Genome-wide identification of the FAD gene family in Persea mericana Mill. and its expression analysis under heat stress.

Avocado (Persea americana Mill.), a high-value tropical fruit tree, faces increasing global warming. Avocado fruit is rich in monounsaturated fatty acids, with fatty acid desaturases (FADs) playing a central role in lipid remodeling and thermal adaptation. In this study, we systematically identified 27 PaFAD genes, classifying them into nine subfamilies, including species-specific expansions of the Fatty Acid Biosynthesis 2 (FAB2) and Fatty Acid Desaturase 1 (FAD1) subfamilies. Using genome-wide characterization, RNA-seq expression profiling and weighted gene co-expression network analysis (WGCNA), we investigated their regulatory roles under heat stress. Transposable element (TE) distribution patterns were examined across PaFAD genes to provide evolutionary insights complementary to their expression profiles. Promoter analysis revealed enrichment of hormone- and stress-responsive cis-elements, and transcriptomic profiling under heat stress indicated distinct expression patterns between tolerant (‘Mantianxing’) and sensitive (‘Hass’) germplasms. Notably, we identified two hub genes, PaSLD2 and PaFAD6, which display cultivar-dependent and opposite expression patterns and are associated with sphingolipid or chloroplast lipid remodeling under heat stress. Together with the enrichment of flavonoid- and histidine-related pathways in the corresponding WGCNA modules, these results reveal a coordinated regulatory framework linking lipid unsaturation, hormone signaling, and antioxidative defense during thermal adaptation. This study therefore provides a clearer mechanistic understanding of FAD-mediated heat response and highlights specific gene targets that may facilitate the molecular breeding of heat-resilient and high-quality avocado cultivars.