High temperature affects synthesis and degradation of anthocyanin in red-fleshed kiwifruit (Actinidia chinensis): pathway and kinetics analysis

It is well known that high temperatures can lead to a decrease in anthocyanin accumulation in plant organs, but there is insufficient understanding of the internal physiological factors that cause this reduction in anthocyanin accumulation. Apart from the inhibition of synthesis by high temperature, it is not clear how the branch pathways, degradation or transport of anthocyanin change dynamically with temperature increase. Taking red-fleshed kiwifruit as the material, we employed UPLC-MS/MS to investigate the levels of intermediate metabolites in the anthocyanin biosynthesis pathway and potential degradation products. The findings indicated that as the temperature rises, the upstream and downstream branch pathways of the anthocyanin synthesis pathway are adjusted accordingly. Lignin metabolism is enhanced, while the downstream anthocyanin and adjacent branch pathways jointly decrease, but the degradation of anthocyanin accelerated, concurrently with a significant decrease in anthocyanin accumulation. Additionally, the content of a representative degradation product, protocatechuic acid, significantly increased. Kinetic analysis demonstrated that as temperature rose (25-40 °C), the degradation rate constant of anthocyanins increased with the half-life decreased, and the critical temperature range for anthocyanin degradation was between 35 and 40 °C. It is confirmed that under high-temperature conditions, the flow of metabolites in the phenylpropanoid pathway of red-fleshed kiwifruit has undergone readjustment. The inhibition of synthesis and the concurrent degradation jointly contribute to the actual accumulation level of anthocyanins. Through RNA-Seq and enzyme activity experiments, we also identified two genes/enzymes that were promoted by high-temperature stimulation, laccase-12-like (Achn037101) and glucan endo-1,3-β-glucosidase (Achn008121). This study reveals the metabolic kinetics of anthocyanin metabolism in red-fleshed kiwifruit in vivo and offers a deeper understanding of anthocyanin degradation in response to high temperature.