Transcriptomic and metabolomic analysis of the mechanism of temperature-regulated anthocyanin biosynthesis in purple asparagus spears

Anthocyanins are the major pigments in purple asparagus spears, and the purple color fades and becomes lighter under high temperature growing conditions. In this study, we examined anthocyanins in the peels of spears and the differential expression of genes related to anthocyanin biosynthesis in the spear peels of purple asparagus plants grown at 25/15 °C (day/night; T1, CK), 32/20 °C (T2), and 38/25 °C (T3) using metabolomic and transcriptomic technologies. By comparing samples grown under the three temperature treatments, a total of 17 anthocyanin metabolites were identified using LC-MS/MS. In comparison groups T1 vs T2 and T1 vs T3, the content of cyanidin 3-O-arabinoside was reduced 27.4- and 65-fold, respectively; the content of delphinidin 3-O-rutinoside was reduced 11.5- and 33.8-fold, respectively. Through transcriptomic analysis, 3,783 and 5,038 differentially expressed genes (DEGs) were found in T1 vs T2 and T1 vs T3 comparison groups, respectively. KEGG analysis indicated that the DEGs were significantly enriched in phenylpropane and flavonoid metabolic pathways. In T1 vs T3, the expression of 14 genes, including CHI, CHS, DFR, and ANS, in the anthocyanin biosynthetic pathway was downregulated; the expression of 14 genes, including HCT, CCR, and CCoAOMT, in the lignin biosynthetic pathway was upregulated; and the expression of the LAR gene in the catechin pathway was upregulated. High temperature conditions caused the redirection of metabolic flux between the branches of the phenylpropane metabolic pathway, and part of the fluxes shifted from the anthocyanin biosynthetic branch to the lignin biosynthetic branch, thereby restricting the synthesis of anthocyanins.