CsWRKY13, a novel WRKY transcription factor of <i>Camellia sinensis</i>, involved in lignin biosynthesis and accumulation

Lignin is an aromatic polymer that provides the necessary mechanical strength for the transport of water and nutrients in higher plants. Lignin biosynthesis and accumulation affect growth and development of tea plant. The degree of lignification related to the tenderness of tea fresh leaves and determines the quality of tea. WRKY transcription factors play central roles in plant development and physiological processes. However, the roles of WRKY transcription factors in lignin biosynthesis of tea plant remain unclear. In this study, a WRKY gene, CsWRKY13, was cloned from tea plant 'Longjing 43'. The open reading frame (ORF) of CsWRKY13 gene was 708 bp, encoding 235 amino acids. Sequence analysis showed that CsWRKY13 contained a conserved WRKYGQK amino acid sequence and a type zinc-finger-like motif CX₄CX₂₃HXH. Subcellular localization showed that CsWRKY13 was localized in the nucleus. The yeast trans-activation assay showed that CsWRKY13 had no transcriptional activity. Expression analysis showed that CsWRKY13 gene was highly expressed in stem. Overexpression of CsWRKY13 in Arabidopsis thaliana reduced lignin content and the expression levels of genes related to lignin biosynthesis in transgenic plants. Most flavonoids pathway related genes were significantly up-regulated. This study shows that CsWRKY13 might function as a negative regulator in regulation of lignin synthesis.