Generating colorful carrot germplasm through metabolic engineering of betalains pigments

Betalains are tyrosine-derived plant pigments exclusively found in the Caryophyllales order and some higher fungi and generally classified into two groups:red-violet betacyanins and yellow-orange betaxanthins.Betalains attract great scientific and economic interest because of their relatively simple biosynthesis pathway,attractive colors and health-promoting properties.Co-expressing two core genes BvCYP76AD1 and BvDODA1 with or without a glycosyltransferase gene MjcDOPA5GT allowed the engineering of carrot(an important taproot vegetable)to produce a palette of unique colors.The highest total betalains content,943.2μg·g^(−1) DW,was obtained in carrot taproot transformed with p35S:RUBY which produces all of the necessary enzymes for betalains synthesis.Root-specific production of betalains slightly relieved tyrosine consumption revealing the possible bottleneck in betalains production.Furthermore,a unique volcano-like phenotype in carrot taproot cross-section was created by vascular cambium-specific production of betalains.The betalains-fortified carrot in this study is thus anticipated to be used as functional vegetable and colorful carrot germplasm in breeding to promote health.