Identification of key gene networks controlling polysaccharide accumulation in different tissues of Polygonatum cyrtonema Hua by integrating metabolic phenotypes and gene expression profiles

Integrative Metabolome and Transcriptome Analyses Reveal the Effects of Plucking Flower on Polysaccharide Accumulation in the Rhizomes of Polygonatum cyrtonema Hua

Polysaccharides are the major bioactive components of Polygonatum cyrtonema Hua, and their biosynthesis and accumulation are influenced by many agronomic practices. In this study, we applied integrative metabolome and transcriptome analyses to investigate the accumulation of bioactive components in one-year-old (1Y) and six-year-old (6Y) rhizomes of P. cyrtonema Hua treated with a plucking flower. The compound content analysis suggested that six-year-old treated rhizomes (T6) accumulated the highest polysaccharide content compared to that of one-year-old treated rhizomes (T1), one-year-old untreated rhizomes (C1), and six-year-old untreated rhizomes (C6). Metabolomics analysis showed that 4-O-galactopyranosylxylose, 6-O-α-l-arabinopyranosyl-d-glucopyranose, d-arabinose and dl-xylose significantly accumulated in T6 rhizomes. Carbohydrate metabolic pathways, including "glycolysis/gluconeogenesis", "pentose and glucoronate interconversions" and "amino sugar and nucleotide sugar metabolism" were highly correlated with polysaccharide biosynthesis and accumulation. The transcriptome data indicated that UPG2, GPI, and GALE were positively upregulated in T6_vs_C6. In parallel, RHM and PEI were down-regulated in T6_vs_C6. Taken together, this study not only indicates that the candidate metabolites/metabolic pathways and genes affected by plucking flowers may influence the accumulation of polysaccharides in the rhizomes but also provides an easy and feasible agronomic practice to facilitate the accumulation of polysaccharides in the rhizomes of P. cyrtonema Hua.

Integrative analysis of the transcriptome and metabolome provides insights into polysaccharide accumulation in Polygonatum odoratum (Mill.) Druce rhizome

Background

Polygonatum odoratum (Mill.) Druce is a traditional Chinese herb that is widely cultivated in China. Polysaccharides are the major bioactive components in rhizome of P. odoratum and have many important biological functions.

Methods

To better understand the regulatory mechanisms of polysaccharide accumulation in P. odoratum rhizomes, the rhizomes of two P. odoratum cultivars 'Y10' and 'Y11' with distinct differences in polysaccharide content were used for transcriptome and metabolome analyses, and the differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) were identified.

Results

A total of 14,194 differentially expressed genes (DEGs) were identified, of which 6,689 DEGs were down-regulated in 'Y10' compared with those in 'Y11'. KEGG enrichment analysis of the down-regulated DEGs revealed a significant enrichment of 'starch and sucrose metabolism', and 'amino sugar and nucleotide sugar metabolism'. Meanwhile, 80 differentially accumulated metabolites (DAMs) were detected, of which 52 were significantly up-regulated in 'Y11' compared to those in 'Y10'. The up-regulated DAMs were significantly enriched in 'tropane, piperidine and pyridine alkaloid biosynthesis', 'pentose phosphate pathway' and 'ABC transporters'. The integrated metabolomic and transcriptomic analysis have revealed that four DAMs, glucose, beta-D-fructose 6-phosphate, maltose and 3-beta-D-galactosyl-sn-glycerol were significantly enriched for polysaccharide accumulation, which may be regulated by 17 DEGs, including UTP-glucose-1-phosphate uridylyltransferase (UGP2), hexokinase (HK), sucrose synthase (SUS), and UDP-glucose 6-dehydrogenase (UGDH). Furthermore, 8 DEGs (sacA, HK, scrK, GPI) were identified as candidate genes for the accumulation of glucose and beta-D-fructose 6-phosphate in the proposed polysaccharide biosynthetic pathways, and these two metabolites were significantly associated with the expression levels of 13 transcription factors including C3H, FAR1, bHLH and ERF. This study provided comprehensive information on polysaccharide accumulation and laid the foundation for elucidating the molecular mechanisms of medicinal quality formation in P. odoratum rhizomes.

Research overview on the genetic mechanism underlying the biosynthesis of polysaccharide in tuber plants

Tuber plants are of great significance in the world as human food crops. Polysaccharides, important metabolites in tuber plants, also serve as a source of innovative drugs with significant pharmacological effects. These drugs are particularly known for their immunomodulation and antitumor properties. To fully exploit the potential value of tuber plant polysaccharides and establish a synthetic system for their targeted synthesis, it is crucial to dissect their metabolic processes and genetic regulatory mechanisms. In this article, we provide a comprehensive summary of the basic pathways involved in the synthesis of various types of tuber plant polysaccharides. We also outline the key research progress that has been made in this area in recent years. We classify the main types and functions of tuber plant polysaccharides and analyze the biosynthetic processes and genetic regulation mechanisms of key enzymes involved in the metabolic pathways of starch, cellulose, pectin, and fructan in tuber plants. We have identified hexokinase and glycosyltransferase as the key enzymes involved in the polysaccharide synthesis process. By elucidating the synthesis pathway of polysaccharides in tuber plants and understanding the underlying mechanism of action of key enzymes in the metabolic pathway, we can provide a theoretical framework for enhancing the yield of polysaccharides and other metabolites in plant culture cells. This will ultimately lead to increased production efficiency.