Gibberellins (GAs) are a class of plant hormones that can affect plant growth and development. GA-oxidases are rate-limiting enzymes, which play a direct role in GA accumulation in plants. However, the roles of GA-oxidase on carrot (Daucus carota L.) taproot development are still unclear. In this study, two GA-oxidase genes, DcGA20ox2 and DcGA2ox1, were identified in carrot. Transgenic carrot plants were obtained by using Agrobacterium-mediated genetic transformation method. The results showed that overexpression of DcGA20ox2 significantly promoted the accumulation of active GAs in carrot, increased plant height, generated more branches, and enhanced xylem development. Overexpression of DcGA2ox1 significantly reduced the total contents of active GAs compared with the control group, resulting in a dwarf phenotype and markedly increased lignin content of the transgenic carrot. The expression profiling showed that the genes of GA metabolic pathway responded to the negative feedback regulation mechanism. At the same time, the expression of most genes in lignin biosynthesis and polymerization process was up-regulated, corresponding to the massive accumulation of lignin. These findings indicated that DcGA20ox2 and DcGA2ox1 affected carrot growth and development by regulating the levels of endogenous GAs. The results from current work might shed light on further studies aimed to regulate lignification in carrot and other crops.

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.