A WD40 Repeat Protein from Camellia sinensis Regulates Anthocyanin and Proanthocyanidin Accumulation through the Formation of MYB–bHLH–WD40 Ternary Complexes.

Flavan-3-ols and oligomeric proanthocyanidins (PAs) are the main nutritional polyphenols in green tea (<italic>Camellia sinensis</italic>), which provide numerous benefits to human health. To date, the regulatory mechanism of flavan-3-ol biosynthesis in green tea remains open to study. Herein, we report the characterization of a <italic>C. sinensis</italic> tryptophan-aspartic acid repeat protein (CsWD40) that interacts with myeloblastosis (MYB) and basic helix-loop-helix (bHLH) transcription factors (TFs) to regulate the biosynthesis of flavan-3-ols. Full length <italic>CsWD40</italic> cDNA was cloned from leaves and was deduced to encode 342 amino acids. An in vitro yeast two-hybrid assay demonstrated that CsWD40 interacted with two bHLH TFs (CsGL3 and CsTT8) and two MYB TFs (CsAN2 and CsMYB5e). The overexpression of <italic>CsWD40</italic> in <italic>Arabidopsis thaliana transparent testa glabra 1</italic> (<italic>ttg1</italic>) restored normal trichome and seed coat development. Ectopic expression of <italic>CsWD40</italic> alone in tobacco resulted in a significant increase in the anthocyanins of transgenic petals. <italic>CsWD40</italic> was then coexpressed with <italic>CsMYB5e</italic> in tobacco plants to increase levels of both anthocyanins and PAs. Furthermore, gene expression analysis revealed that <italic>CsWD40</italic> expression in tea plants could be induced by several abiotic stresses. Taken together, these data provide solid evidence that CsWD40 partners with bHLH and MYB TFs to form ternary WBM complexes to regulate anthocyanin, PA biosynthesis, and trichome development. [ABSTRACT FROM AUTHOR]