The β-ketoacyl CoA synthase encoded by the KCS genes is a rate-limiting enzyme for the synthesis of very-long-chain fatty acid (VLCFA), which catalyzes the VLCFA elongation. Yellow horn (Xanthoceras sorbifolium) is a horticultural tree species known for its kernel oil, which has strong resistance to drought, cold, high temperature, and saline-alkali. The conserved domain FAE1-CUT1-RPPA and ACP-syn-III_C of the KCS gene family were used to search the KCS sequences across the whole genomic sequence of yellow horn; a total of 20 XsKCS genes were identified and divided into four subfamilies. The conserved motif and transmembrane structure analysis revealed that most XsKCSs had a conserved transmembrane domain except XsKCS10 and XsKCS20. The prediction of cis-acting elements of XsKCS genes showed that XsKCS genes contained many stress and hormone response elements, such as ABRE, MBS, and LTR. Furthermore, XsKCS genes exhibited differential expression profiles under abiotic stress and stress-related hormone treatment conditions. Transcriptomic data showed that XsKCS1, XsKCS11, and XsKCS17 had higher expression in yellow horn with high leaf cuticular wax, indicating that they may function in the cuticular wax accumulation and drought response. This study laid a foundation for further functional verification of XsKCS genes in yellow horn stress response.

Spring frost is a major limiting factor in the production and cultivation of apricot kernels, an ecological and economic dry-fruit tree in China. The frequent occurrence of spring frost often coincides with the blooming period of apricot kernels, resulting in significant damage to floral organs and reductions in yield. We investigated the molecular signature of pistils from two apricot kernel cultivars with different frost-resistance levels using transcriptome data. A total of 3223 differently expressed genes (DEGs) were found between two apricot kernel cultivars under freezing stress, including the bHLH and AP2/ERF-ERF transcription factors. Based on KEGG analysis, DEGs were mostly enriched in the biosynthesis of the secondary metabolites, in the metabolic pathways, and in plant-hormone signal transduction. The co-expression network, which included 81 hub genes, revealed that transcription factors, protein kinases, ubiquitin ligases, hormone components, and Ca²⁺-related proteins coregulated the ROS-mediated freezing response. Moreover, gene interaction relationships, such as ERF109-HMGCR1, ERF109-GRXC9, and bHLH13-JAZ8, were predicted. These findings revealed the regulatory factors for differences in frost resistance between the two tested apricot kernel cultivars and contributed to a deeper understanding of the comprehensive regulatory program during freezing stress. Some of the hub genes identified in this work provide new choices and directions for breeding apricot kernels with a high frost resistance.