Abstract
BackgroundStevia rebaudiana (Bertoni) is considered one of the most valuable plants because of the steviol glycosides (SGs) that can be extracted from its leaves. Glycosyltransferases (GTs), which can transfer sugar moieties from activated sugar donors onto saccharide and nonsaccharide acceptors, are widely distributed in the genome of S. rebaudiana and play important roles in the synthesis of steviol glycosides.ResultsSix stevia genotypes with significantly different concentrations of SGs were obtained by induction through various mutagenic methods, and the contents of seven glycosides (stevioboside, Reb B, ST, Reb A, Reb F, Reb D and Reb M) in their leaves were considerably different. Then, NGS and single-molecule real-time (SMRT) sequencing were combined to analyse leaf tissue from these six different genotypes to generate a full-length transcriptome of S. rebaudiana. Two phylogenetic trees of glycosyltransferases (SrUGTs) were constructed by the neighbour-joining method and successfully predicted the functions of SrUGTs involved in SG biosynthesis. With further insight into glycosyltransferases (SrUGTs) involved in SG biosynthesis, the weighted gene co-expression network analysis (WGCNA) method was used to characterize the relationships between SrUGTs and SGs, and forty-four potential SrUGTs were finally obtained, including SrUGT85C2, SrUGT74G1, SrUGT76G1 and SrUGT91D2, which have already been reported to be involved in the glucosylation of steviol glycosides, illustrating the reliability of our results.ConclusionCombined with the results obtained by previous studies and those of this work, we systematically characterized glycosyltransferases in S. rebaudiana and forty-four candidate SrUGTs involved in the glycosylation of steviol glucosides were obtained. Moreover, the full-length transcriptome obtained in this study will provide valuable support for further research investigating S. rebaudiana.
Highlights
Stevia rebaudiana (Bertoni) is considered one of the most valuable plants because of the steviol glycosides (SGs) that can be extracted from its leaves
The results demonstrated that all of the analytical glucosides in the experimental genotypes were clearly varied and provided a potential basis for Weighted gene co-expression network analysis (WGCNA) co-expression network analysis to uncover the glucosyltransferases involved in the biosynthesis pathway of the corresponding glycosides
Data obtained separately from the leaves of the seedling, adult, and budding stages of the ‘023’ genotype revealed that the accumulation of steviol glycosides in S. rebaudiana peaked in the budding period
Summary
Stevia rebaudiana (Bertoni) is considered one of the most valuable plants because of the steviol glycosides (SGs) that can be extracted from its leaves. Stevia rebaudiana (Bertoni) belongs to the Asteraceae family and is one of the only two members (S. rebaudiana and S. phlebophylla) in this genus to produce steviol glycosides (SGs), compounds that appeal to people looking for more natural plant-based low-calorie sustainable sweeteners [1, 2]. With the discovery of new glycosides and the characteristics of genetic heterozygosity of stevia [9, 10], elucidating the biosynthetic pathways (especially for the enzymes in the UDPG-dependent glucosyltransferase (UGT) family, which play a critical role in the production of SGs) and regulatory mechanisms of active SGs has attracted the attention of scientists
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