Transcriptomic Characterization of Nitrate-Enhanced Stevioside Glycoside Synthesis in Stevia (Stevia rebaudiana) Bertoni.

Yuming Sun,Luis Alejandro Jose Mur,Xiaoyang Xu,Haiyan Yuan,Haiying Tong,Yongheng Yang,Ting Zhang

doi:10.3390/ijms22168549

Abstract

Nitrogen forms (nitrate (NO3−) or ammonium (NH4+)) are vital to plant growth and metabolism. In stevia (Stevia rebaudiana), it is important to assess whether nitrogen forms can influence the synthesis of the high-value terpene metabolites-steviol glycosides (SGs), together with the underlying mechanisms. Field and pot experiments were performed where stevia plants were fertilized with either NO3− or NH4+ nutrition to the same level of nitrogen. Physiological measurements suggested that nitrogen forms had no significant impact on biomass and the total nitrogen content of stevia leaves, but NO3−-enhanced leaf SGs contents. Transcriptomic analysis identified 397 genes that were differentially expressed (DEGs) between NO3− and NH4+ treatments. Assessment of the DEGs highlighted the responses in secondary metabolism, particularly in terpenoid metabolism, to nitrogen forms. Further examinations of the expression patterns of SGs synthesis-related genes and potential transcription factors suggested that GGPPS and CPS genes, as well as the WRKY and MYB transcription factors, could be driving N form-regulated SG synthesis. We concluded that NO3−, rather than NH4+, can promote leaf SG synthesis via the NO3−-MYB/WRKY-GGPPS/CPS module. Our study suggests that insights into the molecular mechanism of how SG synthesis can be affected by nitrogen forms.

Highlights

As the global standard of living improves, people are aiming to pursue a healthier lifestyle
Different forms of N fertilization ((NH4 + ) vs. (NO3 − )) did not significantly affect the biomass of stevia leaves. This was reflected in the similarities in total N (TN), total carbon (TC) and C/N ratio between NH4 + - and NO3 − -fed stevia plants (Table 1)
The leaf contents of STV and Reb-C were increased by NO3 − rather than NH4 + treatment (Figure 1B,C)

Summary

Introduction

As the global standard of living improves, people are aiming to pursue a healthier lifestyle. The excessive intake of sugars has increased the risk of dental caries, diabetes, obesity and hyperlipidemia, so that the alternative new sugar crop, stevia Stevia plants are rich in steviol glycosides (SGs), a class of tetracyclic diterpenoid compounds, especially in leaf tissue [3]. SGs can be used as food additives and are sweeter than cane sugar and beet sugar, but have a lesser calorific value. These properties have greatly increased worldwide demand for SGs and resulted in increased commercial cultivation of stevia plants [5,6]. Improving the SG levels in stevia plants through agricultural practices is of vital importance for the development of the stevia industry

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Discussion

Conclusion