Abstract
BackgroundThe 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.ResultsIn 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.ConclusionsPhenotypic, 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.
Highlights
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
We found that the contents of chlorophyll and carotenoid were similar in the two varieties whereas the anthocyanin content of Hongxuan No.1 (HX_1) was significantly higher than that of ZZ_1
We inferred that anthocyanin at low concentrations can’t mask the green color of chlorophylls and color of plants is due to the different relative content of the pigments. These explanations were consistent with those of a previous study on tea [12]. These results indicated that high contents of anthocyanin play critical roles in the redness of leaf of HX_1
Summary
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. Ramie is a perennial herb of Urticaceae widely grown in some Asian countries such as southern China, Laos, Thailand and Indonesia [1]. It is nicknamed “crop with the best fiber quality” in China and has been cultivated for thousands of years. In addition to fiber applications, ramie can be used as high-quality forage resources (rude protein > 20%), especially in southern China where there is lack of high-quality protein feed [2]. As a branch of phenylalanine pathway, anthocyanin synthesis pathway has been well studied in many species. The third stage, is driven by leucoanthocyanidin reductase (LAR), anthocyanidin reductase (ANR), UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT) resulting into procyanidins and anthocyanins of various colors
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