Abstract
Chrysanthemums (Chrysanthemum morifolium Ramat.) exhibit a variety of flower colors due to their differing abilities to accumulate anthocyanins. One MYB member, CmMYB6, has been verified as a transcription regulator of chrysanthemum genes involved in anthocyanin biosynthesis; however, the co-regulators for CmMYB6 remain unclear in chrysanthemum. Here, the expression pattern of CmbHLH2, 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. CmbHLH2 significantly upregulated the CmDFR promoter and triggered anthocyanin accumulation when co-expressed with CmMYB6. Yeast one-hybrid analyses indicated that CmbHLH2 was able to bind directly to the CmDFR promoter. Moreover, yeast two-hybrid assays indicated protein-protein interaction between CmbHLH2 and CmMYB6. These results suggest that CmbHLH2 is the essential partner for CmMYB6 in regulating anthocyanin biosynthesis in chrysanthemum.
Highlights
Chrysanthemum (Chrysanthemum morifolium Ramat.) is one of the most popular ornament plants in the world
Based on the similarities with basic helix-loop-helix (bHLH) verified as being related to anthocyanin biosynthesis in other species, one partial sequence bHLH member was mined from the chrysanthemum Expressed sequence tags (ESTs) database
Phylogenetic analysis of these two members and 174 bHLHs including 158 from Arabidopsis and 14 from other plants, showed that CmbHLH2 was clustered in the subgroup containing sequences related to the regulation of anthocyanin biosynthesis, while CmbHLH1 was in a different subgroup (Fig 1)
Summary
Chrysanthemum (Chrysanthemum morifolium Ramat.) is one of the most popular ornament plants in the world. Flower color is an important trait for its commercial value. There are three classes of pigments that contribute to flower color: flavonoids, carotenoids and betalains [1]. Anthocyanins, which are derived from the phenylpropanoid pathway by a series of enzymes [2], are the most conspicuous class of flavonoids, which contribute to flower color but are important in attracting pollinators, aiding seed dispersal and protecting plants from UV irradiation damage [3,4]. PLOS ONE | DOI:10.1371/journal.pone.0143892 November 30, 2015
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