Identification of , a gene involved in betaxanthin biosynthesis in , 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, , , and , as quinoa orthologs of beet and . Agroinfiltration experiments in revealed that exhibited L-DOPA synthesis activity, whereas did not. To enable large-scale production of betaxanthins, we developed a tobacco BY-2 cell line expressing and , 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.