Differential gene expression of anthocyanin biosynthetic genes under low temperature and ultraviolet-B radiation in bell pepper (Capsicum annuum)

Anthocyanins are colored water-soluble pigments found widespread in plants, which are strongly accumulated during development and under biotic and abiotic stress favoring plant adaptation. Bell pepper (Capsicum annuum L.) exhibits anthocyanin pigmentation during development and abiotic stress conditions, making it an interesting model to study anthocyanin biosynthesis. Therefore, the aim of this study was to investigate the temporal expression of the anthocyanin biosynthetic genes MYB, F3H, F35H, DFR and ANS, in stems from C. annuum plants after exposure to LT, UV-B and combined LT+UV-B. In our study, we found a dramatic upregulation of MYB showing a peak at 16:00 h on day 31 in all treatments. F3H expression was upregulated by LT and LT+UV-B treatments showing a higher increase in the latter. Moreover, F35H and DFR were strongly increased under LT treatments in bell pepper stems. Surprisingly, F3H, F35H and DFR showed no changes in UV-B treatment, while ANS was only slightly upregulated several hours after UV-B radiation suggesting a late response. Based on our findings, anthocyanin biosynthetic genes were more influenced by LT than UV-B in C. annuum stems. The higher expression of F3H under LT+UV-B treatment may denote the biosynthesis of other flavonoids instead anthocyanins to protect plants from combined LT+UV-B stress. Furthermore, the higher increase on DFR expression in comparison to ANS by LT treatment may suggest an enhancement toward proanthocyanidin biosynthesis over anthocyanidin production by ANS. Collectively, our results provide new insights about the transcriptional regulation of anthocyanin biosynthetic genes in response to LT and UV-B alone or in combination in bell pepper stems.