Integrated analysis of transcriptomic and metabolomic reveals the adaptation mechanism in sandalwood (Santalum album L.) under heat stress

Abstract

Global warming intensifies high-temperature stress, threatening the growth and heartwood formation of Santalum album L. To elucidate the molecular basis of the heat-stress response, we conducted transcriptomic and metabolomic analyses on sandalwood seedlings under heat stress. Results showed: (1) Transcriptome identified 2,501 and 866 differentially expressed genes (DEGs) in TR0 vs. TR1 and TR1 vs. TR2 respectively (TD stands for metabolome samples, TR stands for transcriptome samples; suffix numbers correspond to sampling time points: 0 = day 0 before stress, 1 = day 1 of stress, 2 = day 3 of stress), mainly involving pathways such as plant hormone signal transduction, endoplasmic reticulum protein processing, heat shock protein regulation, and reactive oxygen species (ROS) clearance; (2) 26,244 and 20,451 metabolic ion features were detected in the positive and negative ion modes (PI and NI), respectively. The number of differentially expressed metabolites (DEMs) increased with stress time, and key metabolites of phenylpropanoid pathway such as 4-Hydroxycinnamic acid changed significantly. (3) Integrated analysis indicated that phenylpropanoid biosynthesis pathway was core response pathway, with high expression of key enzyme genes (PAL, C4H, 4CL). Expression level of the CHS gene (SA08G01315) in the flavonoid branch was significantly induced, which may be involved in antioxidant defense under heat stress. In the lignin branch, HCT transcript levels increased while COMT decreased sharply—a shift potentially linked to the wilting phenotype on day 3. Crucial enzyme genes like CAD were also highly expressed, indicating enhanced lignin monomer biosynthesis potential. Transcription factors (TFs) including ERF and MYB participated in pathway regulation. This study identified candidate key pathways and genes associated with the heat stress response in sandalwood, providing scientific evidence for subsequent variety improvement, domestication, and mechanistic research on plant thermal adaptation.