Metabolome, transcriptome and physiological analyses provide insight into the color transition of litchi pericarp

Abstract

Litchi is popular around the world for its attractive appearance, exotic flavor and rich nutrition, but the pericarp becomes brown rapidly after harvest, which greatly reduces its shelf life and market value. Both metabolites and gene expression were profiled on a large scale in litchi pericarp at four typical color stages covering from preharvest to postharvest. Through a liquid chromatography tandem mass spectrometry approach, 731 metabolites were identified, of which 385 were differentially metabolized. The flavonoid biosynthetic pathway was enriched based on the analysis of differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) among the four stages. In addition, six common types of anthocyanins were identified, among which cyanidin-3-rutinoside and peonidin-3-glucoside were dominant. Surprisingly, the highest accumulation of metabolites, including flavonoids and anthocyanins, was detected at the green stage, and the abundance of metabolites was positively correlated with the expression of structural and regulatory genes related to their biosynthesis. Among the differentially metabolized phytohormones, abscisic acid (ABA) was more accumulated at the turning and brown stages than at the green and red stages. Epicatechin and procyanidin B2 accumulated greatly from the green to red stages, while their relative contents were reduced by 91.51 % and 64.39 %, respectively, at the brown stage compared to the red stage, indicating their pivotal roles in litchi pericarp browning. In summary, the significant decrease in flavonoid content may be the main cause of brown color formation. This study provides an important foundation for future studies on browning prevention and better utilization of litchi pericarp.