SlAN2 overexpression improves cold resistance in tomato (Solanum lycopersicum L.) by regulating glycolysis and ascorbic acid metabolism.

Chilling stress seriously affects the growth and yield of tomato. Anthocyanin is a typical chilling-induced metabolite with strong antioxidant activity and photoprotective capacity. Here, we found that anthocyanin was also involved in ascorbic acid biosynthesis and glycolysis under chilling stress. SlAN2 is an important positive gene in anthocyanin biosynthesis. The results of physiological indicators showed that SlAN2 overexpression lines (A189) had a greater ability to tolerate cold stress than wild-type (WT) plants. Conjoint analysis of transcriptomics and metabonomics of A189 lines and WT plants was used to analyze the metabolic difference and the cold resistance mechanisms caused by anthocyanin under chilling stress. The anthocyanin accumulated more in A189 than that in WT under chilling stress at 4 °C for 24 h, which led to hexoses and ascorbic acid increased significantly. Results indicate that SlAN2 overexpression reduces the expression of key enzyme genes in glycolytic pathway such as phosphofructokinase (PFK) and pyruvate kinase (PK) genes, weakens glycolysis ability, and promotes accumulation of hexoses in A189 lines at 4 °C for 24 h compared with wild lines. Additionally, ascorbic acid content is increased by up-regulated the genes of ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR). The increased hexose content can reduce cell osmotic potential, freezing point and synthesize more ascorbic acid, while the increased ascorbic acid content can enhance the ability to scavenge reactive oxygen species, so improves the cold resistance of tomato. The glycolysis and ascorbic acid metabolism pathway mediated by SlAN2 provides a new insight for the molecular mechanism of anthocyanins in improving the cold resistance of tomato and provides a new theoretical basis for cultivating new cold-tolerant tomato varieties.