胍代谢在发状念珠藻耐旱中的作用机理研究

The habitats of desiccation-tolerant cyanobacteria are poor in nutrition, and the available nitrogen sources for organisms are strictly limited. However, the unique pathway of nitrogen metabolism and the molecular mechanism of adaptation to extraordinary desiccation remain unknown. In a previous research, through in-depth study of molecular biology, functional genomics and transcriptomics of Nostoc flagelliforme on ecological niche adaptation, we found that desiccation-tolerant cyanobacteria obtained a conserved gene cluster involved in guanidine degradation from proteobacteria through horizontal gene transfer, which might play an important role in providing nitrogen source for protein resynthesis during rehydration. Meanwhile, a conserved Guanidine-I riboswitch was found to be involved in the regulation of the gene cluster expression. Based on the previous results, this project intends to study the correlation between the protein resynthesis in Nostoc flagelliforme and guanidine degradation to reveal the potential biological function of the gene cluster involved in guanidine metabolism. Futher more, the applicant will investigate the physiological characteristics of different strains during rehydration process by phenotype analysis on Guanidine-I riboswitch and guanidine binding site mutants and complementary strains, and to elucidate the mechanism of guanidine metabolism affecting the adaptation of Nostoc flagelliforme to arid and exposed niches. The results will help to expand the understanding of desiccation-tolerant cyanobacteria with guanidine as a new nitrogen source to adapt to extreme drought environments, and it will lay a solid theoretical foundation for guiding future utilization of desiccation-tolerant cyanobacteria for the restoration of desert ecosystem.

耐旱发状念珠藻的生境营养贫瘠，可利用的氮源受到严格限制，然而其独特的氮代谢途径及适应干旱环境的机制尚不清楚。前期通过深入研究发状念珠藻逆境适应的分子生物学、功能基因组学和转录组学，申请人发现耐旱蓝藻通过水平基因转移的方式，从变形菌获得了一个参与胍代谢的基因簇。该基因簇可能在发状念珠藻耐旱复苏过程中，为蛋白质重新合成提供氮源起重要作用。同时，申请人还发现一个保守的胍基核糖开关参与此基因簇的表达调控。本项目拟在此基础上，研究发状念珠藻复水过程中胍代谢与蛋白质重新合成间的相关性，鉴定胍代谢相关基因的功能。通过构建胍基核糖开关与胍结合位点突变株和互补株，分析不同株系在复水过程中的生理生化特性，阐明胍代谢影响发状念珠藻耐旱能力的作用机理。研究结果拓展人们对耐旱蓝藻以胍作为新型氮源适应干旱环境的认知，为培育耐旱蓝藻治理荒漠化奠定理论基础。

发菜作为一种世界性分布的陆生耐旱蓝藻，常年遭受着极端干旱和极强的紫外辐射等非生物胁迫，生境中生物可利用氮源极度匮乏。项目以耐旱蓝藻发菜作为研究对象，旨在研究胍代谢影响其适应干旱环境的作用机理。生物信息学预测出了发菜中胍基核糖开关的二级结构，并在其二级结构中引入点突变与互补突变，通过体外转录合成相应的RNA片段，采用等温滴定量热实验证实了此类核糖开关为胍-I型核糖开关。通过使用高效液相色谱和液相色谱–质谱技术分析胍代谢产物，鉴定了发菜胍代谢相关基因簇的功能。检测以细菌荧光素酶为报告基因的胍基核糖开关式基因表达，结合分析胞内氮含量的变化与此核糖开关作用模式之间的关系，揭示了胍基核糖开关的生物学功能。综上所述，发菜通过水平基因转移的方式获得了一个参与胍代谢的基因簇。该基因簇受到胍基核糖开关的精密调控。胍的降解代谢作为发菜新的氮源利用途径，有助于其适应极端干旱和营养贫瘠的恶劣环境。