Metabolome and Transcriptome Combined Reveal the Main Floral Volatile Compounds and Key Regulatory Genes of Castanea mollissima

Chestnut (<i>Castanea mollissima</i>) is an economically important forest tree species, and its flowers possess functions such as repelling mosquitoes, killing bacteria, and clearing heat. However, the regulatory mechanisms of floral volatile organic compounds (VOCs) in chestnut are still unclear. This study analyzed the contents of major volatile compounds and related gene expression levels in chestnut flowers during the initial flowering stage (IFS) and full-flowering stage (FFS) using metabolomics and transcription techniques. In total, 926 volatile compounds were detected, mainly terpenes, heterocyclic compounds, and esters. Acetylenone, styrene, and β-pinene had contents that exceeded 5% in FFS chestnut flowers. In total, 325 differential metabolites between the IFS and FFS were significantly (<i>p</i> < 0.05) enriched in the biosynthetic pathways of sesquiterpenes and triterpenes, as well as the ethylbenzene metabolic pathway. In total, 31 differentially expressed genes (DEGs) were related to terpenoid biosynthesis. There were only two DEGs related to the ethylbenzene metabolic pathway. In summary, we identified the volatile components of chestnut flowers and analyzed the changes in the contents of major volatile compounds in the flowers and the expression patterns of the related genes. The research results are helpful for understanding the regulation of VOCs in chestnut flowers.