Background: Chrysanthemum (Chrysanthemum morifolium) is a leading ornamental crop worldwide, prized for its diverse flower colors. Green-flowered varieties are rare and highly valued, yet the molecular mechanisms governing their unique coloration, particularly in response to light, are not well understood. Chlorophyll accumulation in petals is the basis for this green phenotype, but the specific transcription factors that mediate light-induced chlorophyll biosynthesis in chrysanthemum flowers remain to be fully elucidated.

Results: In this study, we investigated the molecular basis of greening in chrysanthemum ray florets. Transcriptomic analysis of light-exposed versus dark-treated florets identified a candidate R1-type MYB transcription factor, designated CmREVEILLE2, whose expression was strongly correlated with light-induced chlorophyll accumulation. CmREVEILLE2 was confirmed to be a nuclear-localized protein, and its expression was rapidly and significantly induced by light. Functional characterization using virus-induced gene silencing (VIGS) indicated that downregulating CmREVEILLE2 resulted in a significant reduction in chlorophyll content and a visually attenuated green phenotype in the ray florets. Mechanistically, yeast one-hybrid (Y1H) and dual-luciferase (DLR) reporter assays revealed that CmREVEILLE2 appears to directly bind to the promoters of key chlorophyll biosynthesis genes, including CmHEMA1 and CmPOR, to activate their transcription.

Conclusion: Our findings suggest that CmREVEILLE2 functions as a critical positive regulator in the light signaling pathway associated with green color formation in chrysanthemum flowers. It appears to act by directly promoting the expression of essential chlorophyll biosynthesis genes, thus driving chlorophyll accumulation. This study provides a novel understanding of flower color regulation and identifies CmREVEILLE2 as a key target for the future molecular breeding of green-flowered chrysanthemum cultivars.

Chrysanthemum morifolium, Flower color, Greening, Chlorophyll biosynthesis

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