Gas Chromatography-Mass Spectrometry Metabolites and Transcriptome Profiling Reveal Molecular Mechanisms and Differences in Terpene Biosynthesis in Two Cultivars during Postharvest Ripening.

Terpene aroma compounds are key quality attributes of postharvest nuts, contributing to their commercial value. However, terpene biosynthesis and regulatory networks in different cvs. are still poorly understood. Here, chief cvs. 'Xi Fei' and 'Xiangya Fei' were investigated for their differences in terpene biosynthesis and gene expression levels during postharvest ripening using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) and transcriptomic datasets. A total of 28 and 22 aroma compounds were identified in 'Xi Fei' and 'Xiangya Fei', respectively. Interestingly, differences in aroma composition between the two cvs. were mostly attributed to D-limonene and α-pinene levels as key determinants in nuts' flavor. Further, transcriptome profiling, correlation analysis, and RT-qPCR annotated two novel genes, in 'Xi Fei' and in 'Xiangya Fei', involved in terpene biosynthesis. In addition, six transcription factors (TFs) with comparable expression patterns to and four TFs to were identified via correlation analysis of a volatile and transcriptome dataset to be involved in terpene biosynthesis. Our study provides novel insight into terpene biosynthesis and its regulation at the molecular level in nut and presents a valuable reference for metabolic engineering and aroma improvement in this less explored nut.