A Novel <i>bHLH</i> Transcription Factor Involved in Regulating Anthocyanin Biosynthesis in Chrysanthemums (<i>Chrysanthemum morifolium</i> Ramat.)

<div><p>Chrysanthemums (<i>Chrysanthemum morifolium</i> Ramat.) exhibit a variety of flower colors due to their differing abilities to accumulate anthocyanins. One <i>MYB</i> member, <i>CmMYB6</i>, has been verified as a transcription regulator of chrysanthemum genes involved in anthocyanin biosynthesis; however, the co-regulators for <i>CmMYB6</i> remain unclear in chrysanthemum. Here, the expression pattern of <i>CmbHLH2</i>, which is clustered in the IIIf bHLH subgroup, was shown to be positively correlated with the anthocyanin content of cultivars with red, pink and yellow flower colors, respectively. <i>CmbHLH2</i> significantly upregulated the <i>CmDFR</i> promoter and triggered anthocyanin accumulation when co-expressed with <i>CmMYB6</i>. Yeast one-hybrid analyses indicated that <i>CmbHLH2</i> was able to bind directly to the <i>CmDFR</i> promoter. Moreover, yeast two-hybrid assays indicated protein-protein interaction between <i>CmbHLH2</i> and <i>CmMYB6</i>. These results suggest that <i>CmbHLH2</i> is the essential partner for <i>CmMYB6</i> in regulating anthocyanin biosynthesis in chrysanthemum.</p>