Identification of chalcone isomerase family genes and roles of DnCHI1 in flavonoid metabolism in Dendrobium nobile

<i>Dendrobium nobile</i> is a prized orchid species with both medicinal and ornamental values, known for accumulating flavonoids that contribute to its bioactivity and flower pigmentation. Chalcone isomerase (<i>CHI</i>), a key enzyme in the flavonoid biosynthetic pathway, catalyzes the conversion of chalcone to naringenin, thereby promoting the production of anthocyanins and other flavonoids. In this study, we present the first systematic analysis of the <i>CHI</i> gene family in <i>D. nobile</i>, classifying them into two subfamilies. Expression profiling revealed that <i>DnCHI1</i>, a type IV <i>CHI</i>, is highly expressed in petals, suggesting a potential role in anthocyanin metabolism. Heterologous transient overexpression assays showed that <i>DnMYB90</i> significantly downregulated endogenous <i>PeCHI</i> expression and reduced anthocyanin accumulation, whereas <i>DnCHI1</i> overexpression resulted in a 15-fold increase in anthocyanin content. Dual-luciferase reporter and yeast one-hybrid assays further confirmed that <i>DnMYB90</i> acts as a transcriptional repressor of <i>DnCHI1</i>. These results provide new insights into the regulatory module in anthocyanin biosynthesis in <i>D. nobile</i>, highlighting the functional divergence of <i>CHI</i> genes and their interaction with MYB transcription factors.