A R1-type MYB CmREVEILLE2 regulates light-mediated chlorophyll biosynthesis and green color formation in chrysanthemum flowers

Abstract Chrysanthemum ( Chrysanthemum × morifolium Ramat.) is a widely cultivated ornamental species, among which green-flowered cultivar representing rarity and distinctiveness. However, the underlying mechanisms governing the formation and regulation of green color remain poorly understood. In this study, exposure to high-intensity light resulted in the loss of green coloration in green chrysanthemum, while low-intensity light preserved it during flower opening in chrysanthemum ‘Lv Dingdang’. A R1-type MYB transcription factor, CmREVEILLE2 ( CmRVE2 ), was identified through transcriptomic analysis of flowers subjected to different light intensities (3,000 Lux for low light, LL; 6,000 Lux for moderate light, ML; and 12,000 Lux for high light, HL). CmRVE2 expression was significantly upregulated under HL conditions, while its expression was lower under LL compared to ML. Additionally, CmRVE2 was upregulated by abscisic acid (ABA) and downregulated by gibberellin (GA). Virus-induced gene silencing (VIGS) of CmRVE2 led to a marked increase in chlorophyll content and the upregulation of chlorophyll biosynthesis-related genes, while CmRVE2 overexpression resulted in the opposite trend. Yeast one-hybrid, electrophoretic mobility shift assays (EMSA), and transient activation assays demonstrated that CmRVE2 directly bound to the promoter of CHLI1 , a gene encodes magnesium chelatase I subunit in chlorophyll biosynthesis. Furthermore, CmRVE2 repressed the expression of MAGNESIUM-PROTOPORPHYRIN IX MONOMETHYL ESTER OXIDATIVE CYCLASE1 ( C R D1 ) and PROTOCHLOROPHYLLIDE OXIDOREDUCTASE1 ( PORA1 ), thereby inhibiting chlorophyll synthesis. These findings provide new insights into how CmRVE2 mediates light signaling to negatively regulate chlorophyll biosynthesis in chrysanthemum flowers.