The bast fiber crop ramie can be used as high-quality forage resources, especially in tropical or subtropical region where there is lack of high-quality protein feed. Hongxuan No.1 (HX_1) is a unique ramie variety with a light reddish brown leaf color, which is obviously different from elite cultivar, Zhongzhu No.1 (ZZ_1, green leaf). While, the regulatory mechanism of color difference or secondary metaboliates synthesis between these two varieties have not been studied. In this study, phenotypic, transcriptomic and metabolomic analysis of HX_1 and ZZ_1 were conducted to elucidate the mechanism of leaf color formation. Chromaticity value and pigment content measuring showed that anthocyanin was the main metabolites imparting the different leaf color phenotype between the two varieties. Based on LC/MS, at least 14 anthocyanins were identified in leaves of HX_1 and ZZ_1, and the HX_1 showed the higher relative content of malvidin-, pelargonidin-,and cyanidin-based anthocyanins. Transcriptome and metabolome co-analysis revealed that the up-regulated expression of flavonoids synthesis gene was positively correlated with total anthocyanins accumulation in ramie leaf, and the differentfially expression of “blue gene” (F3’5’H) and the “red gene” (F3’H) in leaves bring out HX_1 metabolic flow more input into the cyanidin branch. Furthermore, the enrichment of glycosylated modification pathway (UGT and AT) and the expression of flavonoid 3-O-glucosyl transferase (UFGT), anthocyanidin reductase (ANR), in leaves were significantly influenced the diversity of anthocyanins between HX_1 and ZZ_1. Phenotypic, transcriptomic and metabolomic analysis of HX_1 and ZZ_1 indicated that the expression levels of genes related to anthocyanin metabolism contribute to the color formation of ramie variety. Anthocyanins are important plant secandary metabilates with many physiological functions, the results of this study will deepened our understanding of ramie leaf color formation, and provided basis for molecular breeding of functional forage ramie.

中文翻译：

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转录组和代谢组分析揭示了与苎麻（Boehmeria nivea (L.) Gaud.）叶色形成相关的花青素生物合成途径

麻类作物苎麻可作为优质牧草资源，特别是在缺乏优质蛋白饲料的热带或亚热带地区。红轩1号（HX_1）是一种独特的苎麻品种，叶色淡红褐色，与优良品种中竹1号（ZZ_1，绿叶）明显不同。而这两个品种之间色差或次生代谢产物合成的调控机制尚未得到研究。在本研究中，对 HX_1 和 ZZ_1 进行表型、转录组学和代谢组学分析，以阐明叶色形成的机制。色度值和色素含量测定表明，花青素是赋予两个品种不同叶色表型的主要代谢产物。基于 LC/MS，在HX_1和ZZ_1的叶片中至少鉴定出14种花青素，其中HX_1中锦葵素、天竺葵素和花青素类花青素的相对含量较高。转录组和代谢组联合分析表明，黄酮类合成基因表达上调与苎麻叶片总花青素积累量、“蓝色基因”（F3'5'H）和“红色基因”的差异表达呈正相关。叶中的 (F3'H) 带出 HX_1 代谢流，更多地输入花青素分支。此外，叶片中糖基化修饰途径（UGT和AT）的富集和黄酮类3-O-葡萄糖基转移酶（UFGT）、花色素还原酶（ANR）的表达显着影响了HX_1和ZZ_1之间花青素的多样性。表型，HX_1和ZZ_1的转录组学和代谢组学分析表明，花青素代谢相关基因的表达水平有助于苎麻品种的颜色形成。花青素是重要的植物次生代谢产物，具有多种生理功能，本研究结果将加深我们对苎麻叶色形成的认识，为功能性牧草苎麻分子育种提供依据。