Studies On The Mechanism Of Plastidic 2 Glucose-6-phosphate Dehydrogenase Involvement In Nitrogen-related Metabolism

The pentose phosphate pathway?OPPP?is one of the classical metabolic pathways in plants.In the process of sugar metabolism,except that sugar is metabolized by the metabolic pathway of TCA,the other major pathway is OPPP.One of the important functions of OPPP is the production of reduced coenzyme II?NADPH?.Glucose-6-phosphate dehydrogenase?G6PD?,the first enzyme of OPPP,is also a rate-limiting enzyme and plays a decisive role in OPPP.In recent years,studies have shown that plastidic G6PD?P2-G6PD?,G6PD2 and G6PD3 in the G6PD family have obvious responses to exogenous nitrate?NO₃^-?,indicating that G6PD2 and G6PD3 may be involved in nitrogen metabolism.However,the mechanisms and metabolic processes are still unclear.Using the model plant Arabidopsis thaliana as material,we discovered that P2-G6PD is involved in the mechanism of nitrogen metabolism by a new way through genetics,molecular biology,and physiological and biochemical patterns.The main results are as follows:1.G6PD2 and G6PD3 genetic mutations g6pd2 and g6pd3 had no significant phenotypic differences with wild type?WT,Col-0?under conventional soil culture conditions.2.g6pd3 showed obvious phenotypic differences with WT under exogenous glutamate?Glu?as the only nitrogen source,which was reflected in the shorter root length of g6pd3 than that of WT and obvious shoot.Differences in chlorophyll reduction and anthocyanin increase exist in g6pd3;the above information indicates that G6PD3 is involved in Glu-related mechanisms.3.No obvious phenotypic differences between WT and g6pd3 were observed with NO₃^-or ammonium?NH₄⁺?as the nitrogen source.4.In addition to g6pd3,the remaining four G6PD family mutants g6pd2,g6pd4,g6pd5,g6pd6 owned by our laboratory had no significant phenotypic differences with WT under the condition of exogenous Glu as a nitrogen source.5.Under the condition of Glu as a nitrogen source,overexpression of G6PD3 gene has a similar phenotype to WT,indicating that increasing G6PD3 gene expression does not make Arabidopsis more adaptable to Glu as a nitrogen source.6.Glu also promoted the lateral root branching of g6pd3 to a greater extent than WT,and the cells in the elongation and mature zones of WT were significantly longer than those of g6pd3,and more primordiums in the mature zones of g6pd3 are observed.7.The results of gene expression showed that G6PD3 gene had obvious response to exogenous NO₃^-and Glu.Additionally NO₃^-and Glu had different inductions for some genes,and different genes also had different responses to these two nitrogen sources..8.Further experiments showed that except Glu,exogenously added Val,Thr,Leu,Asp,Pro and Ile also causes a significant phenotypic difference between WT and g6pd3,indicating that amino acids do participate in these amino acid-related mechanisms.In summary,we discovered a new mechanism of G6PD3 and nitrogen metabolism through a series of experiments.The mutant g6pd3 showed some incompatibility with some amino acids compared with WT,indicating that G6PD3 participates in nitrogen metabolism in a special way.It participates in the amino acid-related mechanisms and acts as an amino acid when exogenously added as a nitrogen source and act as an important role.