NtPHYB1, a homologous gene of Arabidopsis PHYB, positively regulates the content of phenolic compounds in tobacco.

Polyphenols are important secondary metabolites and bioactive compounds in plants. Light is a vital abiotic factor that greatly impacts the content of polyphenols in plants. In spite of their importance the mechanism of polyphenol regulation still remains unknown in tobacco. A phytochrome B homolog, NtPHYB1, was isolated from Nicotiana tabacum cv. K326 to investigate the role of light receptors in the regulation of polyphenol metabolism in tobacco leaves. Furthermore, role of NtPHYB1 in polyphenol metabolism was analyzed by over-expression and RNAi-silencing approaches. Consistent and complemented results indicated involvement of NtPHYB1 in the regulation of polyphenol metabolism in tobacco leaves. Moreover, high levels of NtPHYB1 transcripts favor the accumulation of chlorogenic acid and its isomers, the key polyphenol component in tobacco leaves. Transcriptome analysis was also carried out for exploring the regulation mechanism of NtPHYB1 in the polyphenol metabolism. Compared with WT, 1665 and 1421 differentially-expressed genes were found in NtPHYB1-GFP and NtPHYB1-RNAi transgenic lines, respectively. Among these, about 30 genes were related to phenylpropanoid pathway, which is predominantly involved in synthesis of polyphenols. Further evidences from quantitative RT-PCR confirmed that NtPHYB1 may control phenylpropanoid pathway through regulating the transcription of PAL4 (phenylalanine ammonialyase 4), 4CL1 (4-coumarate:coenzyme A ligase 1) and COMT (caffeic acid 3-O-methyltransferase) genes.