Physiological Biochemistry-Combined Transcriptomic Analysis Reveals Mechanism of Bacillus cereus G2 Improved Salt-Stress Tolerance of Glycyrrhiza uralensis Fisch. Seedlings by Balancing Carbohydrate Metabolism.

Xiang Xiao,Xinhui Zhang,Duoyong Lang,Xin Ma,Zhenggang Guo,Qiuli Wang

doi:10.3389/fpls.2021.712363

Xiang Xiao, Xinhui Zhang + Show 4 more

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https://doi.org/10.3389/fpls.2021.712363

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Abstract

Salt stress severely threatens the growth and productivity of Glycyrrhiza uralensis. Previous results found that Bacillus cereus G2 enhanced several carbohydrate contents in G. uralensis under salt stress. Here, we analyzed the changes in parameters related to growth, photosynthesis, carbohydrate transformation, and the glycolysis Embden-Meyerhof-Parnas (EMP) pathway-tricarboxylic acid (TCA) cycle by G2 in G. uralensis under salt stress. Results showed that G2 helped G. uralensis-accumulating photosynthetic pigments during photosynthesis, which could further increase starch, sucrose, and fructose contents during carbohydrate transformation. Specifically, increased soluble starch synthase (SSS) activity caused to higher starch content, which could induce α-amylase (AM) and β-amylase (BM) activities; increased sucrose content due to the increase of sucrose synthase (SS) activity through upregulating the gene-encoding SS, which decreased cell osmotic potential, and consequently, induced invertase and gene-encoding α-glucosidase that decomposed sucrose to fructose, ultimately avoided further water loss; increased fructose content-required highly hexokinase (HK) activity to phosphorylate in G. uralensis, thereby providing sufficient substrate for EMP. However, G2 decreased phosphofructokinase (PFK) and pyruvate kinase (PK) activities during EMP. For inducing the TCA cycle to produce more energy, G2 increased PDH activity that enhanced CA content, which further increased isocitrate dehydrogenase (ICDH) activity and provided intermediate products for the G. uralensis TCA cycle under salt stress. In sum, G2 could improve photosynthetic efficiency and carbohydrate transformation to enhance carbohydrate products, thereby releasing more chemical energy stored in carbohydrates through the EMP pathway-TCA cycle, finally maintain normal life activities, and promote the growth of G. uralensis under salt stress.

Highlights

In plants, salt stress leads to reduced water uptake, excessive accumulation of toxic elemental ions, and production of reactive oxygen species (ROS) causing oxidative stress (Salimi et al, 2016; Ahmadi et al, 2018)
Salt stress significantly decreased the contents of total soluble sugar (TSS), starch, fructose, sucrose, and the ratio of sucrose/starch, while G2 significantly increased the contents of TSS, starch, fructose, and sucrose in G. uralensis under salt stress (Figure 2)
Present results showed that salt stress inhibited the growth of G. uralensis, and this effect was partly reversed by G2 inoculation (Figure 2), agreeing with previous findings on wheat (Triticum turgidum subsp. durum) (Ibarra-Villarreal et al, 2021), soybean (G. max L.) (El-Esawi et al, 2018), and Artemisia ordosica (Hou et al, 2021)

Summary

Introduction

Salt stress leads to reduced water uptake, excessive accumulation of toxic elemental ions, and production of reactive oxygen species (ROS) causing oxidative stress (Salimi et al, 2016; Ahmadi et al, 2018). This combination of osmotic, ionic, and oxidative effects promotes cellular damage, declines K+ and Ca2+ efficiency, reduces photosynthetic rate, impairs metabolism, and inhibits plant growth and reduces productivity (Salimi et al, 2016; Brahimova et al, 2021). It can be concluded that plants exposed to salt stress are unable to maintain the required carbohydrate and energy levels, and, certain measures must be adopted to regulate carbohydrate metabolism in salt-stressed plants

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