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Acta Prataculturae Sinica ›› 2021, Vol. 30 ›› Issue (5): 42-51.DOI: 10.11686/cyxb2020220

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Boron promotes secretion of extracellular polysaccharides and indole-3-acetic acid by Rhizobium

Yong-gang CHEN(), Wen-juan KANG, Fang WU, Yun A, Shang-li SHI(), Cui-mei ZHANG, Zi-li LI   

  1. College of Grassland Science,Gansu Agricultural University,Lanzhou 730070,China
  • Received:2020-05-13 Revised:2020-06-29 Online:2021-05-20 Published:2021-04-16
  • Contact: Shang-li SHI

Abstract:

The aim of this study was to determine how boron promotes the production of extracellular polysaccharides and indole-3-acetic acid (IAA) by the Rhizobium strain gn5f. A label-free protein quantitative technique was used to analyze the effect of boron on the protein expression of Rhizobium strain gn5f. The results showed that 100 mg?L-1 was the optimum boron concentration for inducing polysaccharide and IAA production by Rhizobium strain gn5f. A comparison between the control (no boron) and the 100 mg?L-1 boron treatment identified 54 differentially expressed proteins; 7 up-regulated proteins and 47 down-regulated proteins. Bioinformatics analysis showed that these differentially expressed proteins were related to energy production and conversion, fatty acid β-oxidation, gluconeogenesis, amino acid metabolism, and various metabolic processes. The proposed mechanism by which boron promotes the production of extracellular polysaccharides and IAA by Rhizobium gn5f is as follows: boron up-regulates NAD-dependent succinate-semialdehyde dehydrogenase, acetyl-coenzyme A synthetase, and succinate-semialdehyde dehydrogenase (NADP+), which promote metabolic pathways related to the tricarboxylic acid cycle such as pyruvate metabolism, γ-aminobutyric acid (GABA) bypass metabolism, and glutamate metabolism. The energy and various carbohydrates (D-galactose and D-glucose residues, D-glucuronic acid) provided by these metabolic pathways promote the synthesis of extracellular polysaccharides. Finally, IAA is synthesized from tryptophan via indole-3-acetamide (IAM) or indole-3-pyruvate under the action of related enzymes, and boron contributes to this process by improving tryptophan synthesis.

Key words: boron, rhizobia, extracellular polysaccharides, IAA, proteomics