Identification of two terpenoids that accumulate in Chinese water chestnut in response to fresh-cut processing

As a form of vegetable in China, freshly cut corms of Chinese water chestnuts (Eleocharis dulcis) are well received by consumers. Few studies have investigated the metabolites present in fresh-cut E. dulcis, particularly during the storage stage. Two compounds, triterpenoids and apocarotenoids, were identified in fresh-cut E. dulcis during the late storage period using thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and nuclear magnetic resonance (NMR) spectroscopy. The content of these two compounds gradually increased in the surface tissue of fresh-cut E. dulcis during storage. Moreover, the transcript levels of 10 genes involved in terpenoid backbone biosynthesis and five genes involved in carotenoid precursor biosynthesis were evaluated via quantitative real-time PCR (qRT-PCR). Expression of the rate-limiting enzyme-coding genes CwDXS and CwHMGS was significantly induced by wounding. CwMYC and CwbHLH18, which belong to bHLH transcription factors (TFs) IIIe and VIa subgroup, were isolated from E. dulcis corm. Phylogenetic analysis showed that CwMYC and CwbHLH18 grouped with other terpenoid-regulated bHLHs, and their transcript levels were strongly induced after fresh-cut processing. These results suggested that the biosynthesis of terpenoids and apocarotenoids in fresh-cut E. dulcis strongly depended on the transcriptional regulation of structural genes involved in the methylerythritol 4-phosphate (MEP) and mevalonate (MVA) pathways. However, the complex secondary metabolism of fresh-cut E. dulcis during late storage requires further investigation.