Metabolomic and transcriptomic analyses provide insights into temperature and light regulated anthocyanin accumulation in flesh of 'Furongli' plum ( Prunus <underline>salicina</underline> Lindl.)

Anthocyanins are health-promoting pigments that contribute to the quality of fruits. Anthocyanin biosynthesis is affected by light and temperature. However, there is no information available on the effects of light and temperature on anthocyanin accumulation in plum flesh. In this study, we investigated the effects of temperature and light on anthocyanin accumulation in postharvest 'Furongli' plum (Prunus salicina Lindl.) flesh and found that 20oC promoted anthocyanin accumulation with or without light. However, no significant anthocyanin accumulation was detected in the flesh of plums treated with 30 oC/light. RNA-Seq analysis showed that the transcript levels of anthocyanin accumulation-related genes in the flesh were upregulated by 20oC/light and 20oC/ dark treatments. Moreover, several genes involved in sucrose metabolism as well as plant hormone biosynthesis and signal transduction were transcriptionally correlated with anthocyanin accumulation. NAA treatment confirmed that auxin promoted anthocyanin accumulation in plum flesh. Transcription factors differentially regulated by temperature and light were identified. The anthocyanin MYB activator, PsMYB10.2, was only upregulated in the flesh of 20oC/light and 20oC/dark treated fruits, wheras the anthocyanin repressor, PsMYB18, was upregulated in flesh of fruits under all treatment conditions. The PsMYB10.2 promoter was responsive to light, but not to temperature. Transient overexpression assays showed that PsMYB18 inhibited PsMYB10.2 and PsbHLH3 induced anthocyanin accumlation in tobacco leaves. Dual luciferase assays further showed that PsMYB18 repressed the activation activity of PsMYB10.2 on the promoters of PsANS, PsUFGT and PsGST. Yeast one-hybrid and dual luciferase assays showed PsMYB10.2 could bind to and activated the PsMYB18 promoter. These results suggest that temperature and light modulate anthocyanin accumulation in the flesh of 'Furongli' plum by regulating the expression of structural genes involved in anthocyanin accumulation via the cooperation of anthocyanin regulators PsMYB10.2 and PsMYB18.