UV-B pre-irradiation-promoted flavonoid accumulation enhances cold tolerance in tea plants by mediating CsHY5 pathways

Abstract

Flavonoids derived from the phenylpropane pathway are polyphenolic secondary metabolites in plants, which are involved in various processes of plant growth and abiotic stress. Based on metabolome and transcriptome analysis, we speculated that UV-B irradiation may be a convenient method to improve the cold resistance of tea plants. In our study, tea plants pre-irradiated with 2 μmol·m^-2·s^-1 UV-B exhibited a cold tolerant phenotype at -4 °C. HY5 plays a pivotal role in mediating the crosstalk between light and temperature signaling pathways in plants. To further explore the internal mechanisms, the role of CsHY5, acted as UV-B photoreceptors, in cold tolerance was investigated. CsHY5-silenced in tea leaves dramatically impaired UV-B pre-irradiation-enhanced effects on cold tolerance of tea plants, also the contents of flavonoid and the downstream gene expression level of CsMYB12, CsFLS, CsDFR, CsUGT78A14 and CsANR in CsHY5-silenced tea leaves were significantly decreased. On the contrary, CsHY5 overexpression lines of in Arabidopsis thaliana pre-irradiated with UV-B significantly elevated cold tolerance, and the higher flavonoid content and AtFLS, AtDFR and AtANR expression level was detected compared with WT under cold stress. Therefore, our study indicated UV-B preirradiation of tea plants enhances cold tolerance by inducing CsHY5 expression and triggering an increase in flavonoid accumulation.