Comparative Transcriptome Analysis Reveals the Molecular Mechanism of UV-B Irradiation in Promoting the Accumulation of Phenolic Compounds in Wounded Carrot

Abstract

Ultraviolet B (UV-B) irradiation has been demonstrated to play a synergistic effect with wounding in enhancing the accumulation of phenolic antioxidants in carrots. However, little is known about the molecular mechanisms of UV-B treatment on wounded carrots. In this study, wounded carrots were exposed to different doses of UV-B light, then stored at 15 °C for 2 d. The results showed that the content of phenolic compounds in 1 KJ m−2 UV-B–treated samples was 415% and 247% higher than that of whole and wounded carrots, respectively. Based on this, 1 KJ m−2 was selected as the optimal dose of UV-B treatment and used for further analysis. In addition, UV-B treatment greatly enhanced the enzyme activity of phenylalanine ammonia lyase (PAL) and the contents of phenolic profiles, especially 3-O-caffeoylquinic acid (3-CQA). Transcriptome analysis found that UV-B treatment could accelerate the KEGG pathways involved in signal transduction and secondary substance metabolism. The differentially expressed genes (DEGs) in phenolics biosynthesis–related metabolic processes of shikimate pathway and phenylpropanoid biosynthesis were extensively upregulated by UV-B treatment. Our results provided fundamental information for a better understanding of the molecular regulation mechanism of UV-B treatment in promoting the accumulation of phenolic compounds in wounded carrots.