Betalain has received increased attention because of its high nutritional value and crucial physiological functions. Based on the elucidation of its core biosynthetic pathway, betalain can be produced in additional plants by metabolic engineering. Synthesis of betalain in carrot (Daucus carota L.) can improve its nutritional quality and economic value by extracting betalain from the fleshy root, non-edible part, and processing residue of carrot. In this study, two different constructs, namely, pYB:mCD (AomelOS, BvCYP76AD1S, and BvDODA1S) and pYB:CDD (BvCYP76AD1S, BvDODA1S, and MjcDOPA5GTS), were introduced into carrot for betanin synthesis by Agrobacterium-mediated transformation. Betanin can be synthetized in both transgenic calli, and pYB:mCD-transgenic callus can be used to produce betacyanin by suspension culture. However, pYB:mCD-transgenic seedlings can synthetize betanin only by tyrosine feeding. The pYB:CDD-transgenic lines can synthetize betanin in whole plants. The betanin content in fleshy root of pYB:CDD-transgenic carrot was (63.4 ± 9) μg ·g⁻¹ fresh weight according to quantitative analysis. These betanin-producing carrot plant materials can be used to synthesize betanin for industrial application or consumption as dietary sources.

Commonly used reporters rely on a single property, such as the fluorescence of GFP and visible color of anthocyanins, therefore these reporters hardly handle the complicated condition in practice. Betaxanthins are a group of plant natural products derived from the amino acid tyrosine. Its visible yellow-orange color and green fluorescence under blue light make it a promising new reporter. Only two enzymatic reactions are required to convert tyrosine into betaxanthins. Here, we synthesized an open reading frame named Bx that contained all the betaxanthins biosynthetic genes and demonstrated its use as a powerful and efficient reporter in tobacco, carrot, and tomato.