Date Published: April 25, 2019
Publisher: Public Library of Science
Author(s): Shengcai Liu, Xueli Zheng, Junfei Pan, Liyun Peng, Chunzhen Cheng, Xiao Wang, Chunli Zhao, Zihao Zhang, Yuling Lin, Xu XuHan, Zhongxiong Lai, Haitao Shi.
Amaranth plants contain large amounts of betalains, including betaxanthins and betacyanins. Amaranthin is a betacyanin, and its molecular structure and associated metabolic pathway differ from those of betanin in beet plants. The chlorophyll, carotenoid, betalain, and flavonoid contents in amaranth leaves were analyzed. The abundance of betalain, betacyanin, and betaxanthin was 2–5-fold higher in the red leaf sectors than in the green leaf sectors. Moreover, a transcriptome database was constructed for the red and green sectors of amaranth leaves harvested from 30-day-old seedlings. 22 unigenes were selected to analyze the expression profiles in the two leaf sectors. The RNA-sequencing data indicated that many unigenes are involved in betalain metabolic pathways. The potential relationships between diverse metabolic pathways and betalain metabolism were analyzed. The validation of the expression of 22 selected unigenes in a qRT-PCR assay revealed the genes that were differentially expressed in the two leaf sectors. Betalains were biosynthesized in specific tissues of the red sectors of amaranth leaves. Almost all of the genes related to betalain metabolism were identified in the transcriptome database, and the expression profiles were different between the red sectors and green sectors in the leaf. Amaranth plants consist of diverse metabolic pathways, and the betalain metabolic pathway is linked to a group of other metabolic pathways.
Plant pigments mainly include anthocyanins, betalains, carotenoids, and chlorophylls . Anthocyanins are commonly used as natural colorants [2–5]. However, betalains, which are water-soluble nitrogen pigments, are not only more hydrophilic and have a higher tinctorial strength, they also have physiological functions, including anti-oxidative  and anti-cancer . activities. Thus, betalains may be useful for developing novel products relevant to the food and medical industries.
In amaranth plants, betalain metabolism is associated with a group of metabolic pathways. Additionally, multiple source–sink relationships exist between betalain biosynthesis and the synthesis of other metabolites.
Quantitative results of the gene expression and component contents analyses were presented in terms of means ± SDs of at least three biological replicates. The gene expression and component contents were analysed by one-way analysis of variance (ANOVA) followed by Duncan’s test using SPSS version 19.0. These pictures were made using the GraphPad Prism 6.0 software and Excel 2013.