What question did this study set out to answer?

The aim is to investigate how the CcMYB24 transcription factor regulates flavonoid production in orchid leaves.

March 4, 2026BMC Plant Biology0 citationsOpen Access

CcMYB24 redirects flavonoid metabolic flux toward flavonols by activating CcFLS and CcCHI to drive leaf variegation in Cymbidium

GYGuansong YangYunnan Agricultural University CYChuang YanYunnan Agricultural University QZQinghua ZhangXinjiang Medical University

Key Points

The aim is to investigate how the CcMYB24 transcription factor regulates flavonoid production in orchid leaves.
Identified CcMYB24 as a candidate regulator based on transcript levels in variegated leaf sectors.
Established a transformation protocol using Agrobacterium in Dendrobium officinale, achieving about 2.1% efficiency.
Generated CcMYB24 overexpression lines to assess impacts on flavonoid content and leaf color.
Ectopic expression of CcMYB24 led to a 2-fold increase in flavonol content without significantly altering chlorophyll or carotenoid levels.
Stable yellow-green leaf phenotype was achieved in transformed D. officinale.
CcMYB24 activates promoters of CcFLS and CcCHI, enhancing flavonoid metabolism.

Abstract

Leaf color polymorphism strongly influences the ornamental and commercial value of orchids, yet the transcriptional mechanisms that partition flavonoid flux between flavonols and anthocyanins in variegated leaves remain poorly resolved, especially in monocots. Based on our previous findings in γ-ray-induced hybrid Cymbidium cultivars, the R2R3-MYB transcription factor CcMYB24 was identified as a candidate regulator. Its transcript levels were selectively enhanced in the yellow leaf sectors and showed positive correlation with flavonol content, suggesting its potential role in the metabolic partitioning of flavonoids. To functionally test the regulatory capacity of CcMYB24 in a tractable orchid system, we established an optimized Agrobacterium-mediated protocorm transformation protocol in Dendrobium officinale (transformation efficiency ~ 2.1%) and generated CcMYB24-overexpression lines. In D. officinale, ectopic expression of CcMYB24 resulted in substantial increases in flavonol (~ 2-fold) and total flavonoid contents without significantly altering chlorophyll or carotenoid levels, producing a stable yellow-green foliar phenotype (RHS Green Group 143). Dual-luciferase reporter assays showed that CcMYB24 activates the promoters of CcFLS and CcCHI, while yeast one-hybrid and EMSA assays revealed preferential binding to the MYB core motif 5′-CTACC-3′. UV-B (Ultraviolet-b radiation) irradiation further enhanced this regulatory module by elevating CcMYB24 transcript abundance and amplifying flavonol accumulation. Our study establishes the first monocot model demonstrating that a single MYB transcription factor (CcMYB24) orchestrates spatial leaf variegation through coordinated transcriptional activation and preferential flux partitioning, defining a CcMYB24-CcFLS/CcCHI regulatory module with conserved capacity to bias flavonoid output toward flavonols in orchids. These findings provide new insights into the regulatory basis of flavonoid flux partitioning in planta and offer a molecular tool for precision breeding of patterned orchid cultivars.

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