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热凝胶是土壤杆菌在环境氮源限制时产生的水不溶性多糖,其合成与氮源代谢调控相关,但其机理还不清楚。作者使用荧光定量PCR的方法比较了土壤杆菌野生菌株和其ntrC突变株在氮源充足和限制条件下氮源代谢相关基因和碳代谢相关基因的转录水平差异,探索了土壤杆菌对氮源限制环境的应答机制及氮源调控蛋白NtrC和热凝胶合成之间的关系。结果表明土壤杆菌在环境氮源限制时,ntrB,glnA,glnB,nifR等4种氮代谢相关基因和exoC,exoN,crd,cisY,ndk,glmU等6种碳代谢基因的相对转录水平都有不同程度的提高,表明当环境氮源缺乏时土壤杆菌调整细胞整体代谢(包括氮源吸收代谢、碳代谢、能量合成等),同时使碳代谢流进入热凝胶合成途径用于能量储存。NtrC蛋白参与调控热凝胶合成,而且热凝胶合成过程相关酶的调控,除了存在转录水平调控外,还可能还存在翻译水平的调控。ntrC突变株的热凝胶合成能力相对于野生菌显著降低,且热凝胶合成基因crd在氮源缺乏时的相对转录水平较野生菌株高,推测NtrC蛋白并非crd基因的转录因子。
Thermogels are water-insoluble polysaccharides produced by Agrobacterium when it is limited by environmental nitrogen sources. Its synthesis is related to the regulation of nitrogen metabolism, but its mechanism is not clear. The authors compared the transcriptional levels of genes related to nitrogen metabolism and carbon metabolism related genes in Agrobacterium wild-type strains and their ntrC mutant strains using fluorescence quantitative PCR and explored the effect of Agrobacterium on the nitrogen-limited environment Response mechanism and the relationship between nitrogen source regulatory protein NtrC and thermosynthesis. The results showed that the relative transcriptional levels of four nitrogen metabolism related genes (ntrB, glnA, glnB and nifR) and six carbon metabolism genes such as exoC, exoN, crd, cisY, ndk and glmU were all different The degree of improvement indicates that Agrobacterium mediates the overall cellular metabolism (including nitrogen uptake and metabolism, carbon metabolism, energy synthesis, etc.) when environmental nitrogen sources are lacking, while allowing carbon metabolism to flow into the thermal gel synthesis pathway for energy storage. NtrC protein is involved in the regulation of thermogel synthesis, and the regulation of enzymes involved in the synthesis of thermogels, in addition to the regulation of transcriptional level, may also regulate the translational level. The thermal gel synthesis ability of ntrC mutant strain was significantly lower than that of wild strain, and the relative transcriptional level of crd gene in crd gene was not higher than that in wild strain. It is speculated that NtrC protein is not the transcription factor of crd gene.