Betalains are tyrosine-derived red-violet and yellow pigments found exclusively in plants of the Caryophyllales order,which have drawn both scientific and economic interest.Nevertheless,research into betalain chemistry,biochemistry,and function has been limited as comparison with other major classes of plant pigments such as anthocyanins and carotenoids.The core biosynthetic pathway of this pigment class has only been fully elucidated in the past few years,opening up the possibility for betalain pigment engineering in plants and microbes.In this review,we discuss betalain metabolism in light of recent advances in the field,with a current survey of characterized genes and enzymes that take part in betalain biosynthesis,catabolism,and transcriptional regulation,and an outlook of what is yet to be discovered.A broad view of currently used and potential new sources for betalains,including utilization of natural sources or metabolic engineering,is provided together with a summary of potential applications of betalains in research and commercial use.