One gene, two pathways: A master switch boosts polysaccharides and pigments in Dendrobium officinale

Bioactive polysaccharides are the primary medicinal components of Dendrobium officinale, yet the transcriptional regulation underlying their biosynthesis has remained largely unclear. A new study identifies DoMYB75, a subgroup 6 R2R3-MYB transcription factor, as a central regulator that directly activates genes responsible for mannan polysaccharide synthesis. Remarkably, DoMYB75 also promotes anthocyanin accumulation by activating key structural genes in the flavonoid pathway. Functional analyses demonstrate that overexpression of DoMYB75 increases mannose and glucose levels in water-soluble polysaccharides, enhances anthocyanin pigmentation, boosts antioxidant capacity, and improves drought tolerance. These findings reveal a coordinated regulatory mechanism linking primary and secondary metabolism in a valuable medicinal orchid.

Polysaccharides derived from D. officinale are widely recognized for their antioxidant and immunomodulatory properties and serve as key quality markers in commercial products. Mannan-type polysaccharides, synthesized mainly by CELLULOSE SYNTHASE-LIKE A (CSLA) enzymes, represent the dominant bioactive fraction. Although structural genes involved in mannan formation have been characterized, their upstream regulatory mechanisms remain poorly understood. Meanwhile, subgroup 6 R2R3-MYB transcription factors are well known for controlling anthocyanin biosynthesis but have rarely been linked to polysaccharide metabolism. Given the economic and medicinal importance of D. officinale, and the lack of clarity regarding coordinated metabolic regulation, further in-depth investigation is required to elucidate the transcriptional control of polysaccharide biosynthesis.

Researchers from the South China Botanical Garden, Chinese Academy of Sciences, together with collaborators from Fujian Agriculture and Forestry University, reported (DOI: 10.1093/hr/uhaf291) the findings in Horticulture Research (2026). The team functionally characterized DoMYB75 in D. officinale, demonstrating that this transcription factor simultaneously regulates mannan polysaccharide biosynthesis and anthocyanin accumulation. Through molecular, biochemical, and genetic analyses, the study establishes DoMYB75 as a dual regulator that integrates metabolic pathways associated with medicinal compound production and stress adaptation.

The study began with a striking phenotypic observation: purple-stem cultivars of D. officinale accumulated not only higher anthocyanin levels—approximately 12-fold greater than green-stem types—but also significantly elevated water-soluble polysaccharide content. Expression analyses revealed that DoMYB75 was strongly upregulated in purple stems and predominantly expressed in stem tissues, the primary site of polysaccharide storage.

Subcellular localization confirmed that DoMYB75 is a nuclear protein with transcriptional activation activity. Promoter analyses identified secondary wall MYB-responsive elements (SMREs) within the promoters of DoCSLA3, DoCSLA9, and DoCSLA12. Yeast one-hybrid assays, electrophoretic mobility shift assays, and dual-luciferase reporter analyses demonstrated that DoMYB75 directly binds to these promoters and activates their transcription.

Functional validation further supported its role. Silencing DoMYB75 significantly reduced mannose and glucose content in water-soluble polysaccharides, whereas overexpression markedly increased these monosaccharide levels. Intriguingly, DoMYB75 also directly bound to the promoter of DoANS, a key anthocyanin biosynthetic gene, promoting pigment accumulation. Transgenic lines exhibited enhanced antioxidant capacity and improved regeneration under PEG-induced drought stress, highlighting a physiological advantage linked to metabolic enhancement.

“This is the first evidence that a subgroup 6 MYB transcription factor directly regulates mannan biosynthesis in orchids,” the authors noted. “By demonstrating that DoMYB75 activates both DoCSLA and DoANS genes, we uncover a coordinated regulatory module that connects primary carbohydrate metabolism with secondary metabolite production.” The researchers emphasized that such dual-function regulators may represent an evolutionarily conserved strategy for optimizing both metabolic output and environmental resilience.

The discovery of DoMYB75 as a master coordinator offers valuable genetic resources for breeding high-quality D. officinale cultivars with enhanced medicinal value. By simultaneously increasing bioactive polysaccharide accumulation and antioxidant-rich anthocyanin production, targeted manipulation of this transcription factor could improve both pharmacological quality and stress tolerance. Moreover, the findings broaden our understanding of how plants integrate metabolic pathways to balance growth, defense, and adaptation. Beyond orchids, this work provides a conceptual framework for engineering coordinated metabolic enhancement in other medicinal and horticultural crops, potentially advancing sustainable production under increasingly challenging environmental conditions.

###

References

DOI

10.1093/hr/uhaf291

Original Source URL

https://doi.org/10.1093/hr/uhaf291

Funding information

This work was supported by the National Natural Science Foundation of China (grants 32370384 and 32200298), the Guangdong Science and Technology Plan Project (grant 2023B1212060046), and the Guizhou Provincial Basic Research Program (Natural Science) (grant ZK[2023]454).

About Horticulture Research

Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.