DoHY5/DoPIF5- <i>DoPHT1</i> Module Mediates Red-Light Modulation of Phosphorus Homeostasis in <i>Dendrobium officinale</i> Kimura et Migo

<i>Dendrobium officinale</i> Kimura et Migo, a valuable medicinal orchid, thrives in mountainous environments, the specific habitat factors promoting polysaccharide accumulation in wild plants. This study explored how light regulates phosphorus uptake in <i>D. officinale</i> and how light and phosphorus interact to influence polysaccharide synthesis. We found that red light promoted phosphorus absorption and induced polysaccharide accumulation under low phosphorus. Transcriptomic analysis revealed the upregulated expression of phosphate transporters <i>DoPHT1;2</i> and <i>DoPHT1;6</i> under red light. Transcription factors DoHY5 and DoPIF5 directly bound to the promoters of <i>DoPHT1</i> genes and regulated the transporter expression. Additionally, DoPHT1;2 and DoPHT1;6 localized to the cell membrane and functioned as high-affinity phosphate transporters. Overexpression of <i>DoHY5</i> enhanced phosphorus uptake and <i>DoPHT1</i> expression in both <i>Arabidopsis thaliana</i> and <i>D. officinale</i>, whereas DoPIF5 inhibited these processes. In conclusion, the DoHY5/DoPIF5-<i>DoPHT1</i> module mediates the red-light regulation of phosphorus uptake, providing a theoretical foundation for improving the cultivation and quality of <i>D. officinale</i>.