Identification of <i>CqCYP76AD5v1</i>, a gene involved in betaxanthin biosynthesis in <i>Chenopodium quinoa</i>, and its product, betaxanthin, which inhibits amyloid-β aggregation

Betalain pigments, primarily produced by the order Caryophyllales, are categorized into betacyanins (red/purple) and betaxanthins (yellow/orange). While the biosynthetic pathways of these pigments are well-studied, the genes responsible for betaxanthin biosynthesis in quinoa were previously unknown. This study identified three candidate genes, <i>CqCYP76AD5v1</i>, <i>CqCYP76AD5v2</i>, and <i>CqCYP76AD130</i>, as quinoa orthologs of beet <i>CYP76AD5</i> and <i>CYP76AD6</i>. Agroinfiltration experiments in <i>Nicotiana benthamiana</i> revealed that <i>CqCYP76AD5v1</i> exhibited L-DOPA synthesis activity, whereas <i>CqCYP76AD130</i> did not. To enable large-scale production of betaxanthins, we developed a tobacco BY-2 cell line expressing <i>CqCYP76AD5v1</i> and <i>CqDODA1-1</i>, with vulgaxanthin I identified as the predominant product. Furthermore, the betaxanthin mixture extracted from this line inhibited amyloid-β (Aβ) aggregation, a key factor associated with Alzheimer's disease. These findings demonstrate the potential of betaxanthins derived from quinoa betaxanthin-biosynthesis genes for applications in health supplements and pharmaceuticals.