Genetics of Betalain Pigments in Amaranth Species

Abstract

Amaranth is an ancient pseudo-cereal that has been gaining research attention in recent years due to its tolerance to harsh climates, a high seed protein content and its secondary metabolites, such as betalain pigments. Betalains have been reported to have a broad spectrum of applications, ranging from human nutrition, pharmaceutical potential, crop enhancement, and antimicrobial properties. Several members of the Amaranthaceae family produce red (betacyanin) and/or yellow (betaxanthin) betalain pigments, which are chemically distinct from anthocyanins, the pigment responsible for red and blue coloration in most other plants. Although the specific roles of betalains in plant physiology are not fully understood, they are known to be involved in attracting pollinators and further hypothesized to be involved in responses against biotic and abiotic stresses. With a recent focus on sequencing and genomics in amaranth, reverse genetic tools are being developed and applied for functional gene annotation and characterization of betalain biosynthesis pathway genes via transient transformation methods. To better understand betalain genetics, this chapter presents the current status of research in Amaranthus species concentrating on the types of betalains found, their biosynthesis pathway, the evolution of pathway genes, and their ecological and physiological significance in the plant. Together, this information will create a spotlight for future research on betalain biosynthesis and will lead to the development of improved strategies to fully uncover the biological role of these pigments.