硼对根瘤菌胞外多糖和吲哚乙酸分泌的调控研究

为探究硼促进根瘤菌gn5f产胞外多糖和吲哚乙酸的调控机制，采用Label free蛋白质定量技术，分析硼对根瘤菌gn5f差异蛋白表达的影响。结果表明，最适硼浓度为100 mg?L^-1，该浓度可以显著促进根瘤菌gn5f胞外多糖和吲哚乙酸（IAA）的分泌，同时最适浓度处理根瘤菌gn5f共鉴定到54个差异表达蛋白，其中7个上调蛋白，47个下调蛋白。生物信息学分析表明，这些差异蛋白与能量产生及转化，脂肪酸β氧化、糖异生、氨基酸代谢及各种代谢酶类等有关。100 mg?L^-1硼促进根瘤菌gn5f产胞外多糖和IAA的机制为：硼通过促进烟酰胺腺嘌呤二核苷酸（NAD）依赖性琥珀酸半醛脱氢酶、乙酰辅酶A合成酶、琥珀酸半醛脱氢酶（NADP⁺）等差异蛋白上调，继而促进丙酮酸代谢、γ-氨基丁酸（GABA）旁路代谢，谷氨酸代谢等与三羧酸循环有关的代谢通路，为胞外多糖合成提供能量及所需要的各种前体物质（D-半乳糖残基，D-葡萄糖残基以及D-葡萄糖醛酸等），进而促进胞外多糖的合成；硼促进色氨酸合成，色氨酸在相关酶的作用下经吲哚-3-乙酰胺（IAM）或吲哚-3-丙酮酸途径合成IAA，继而促进IAA的合成。

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

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.