Regulation of dual nitrogenases in response to nitrogen stress in a cyanobacterium

蓝藻是古老的微生物，是地球上最早产生氧气的生物之一。今天，蓝藻是环境中重要的生物。它们的能量来自阳光，碳来自空气中的二氧化碳，氮气来自空气中的氮气。它们不仅作为自由生活的有机体很重要，而且作为许多与植物和真菌共生的伙伴也很重要。蓝藻鱼腥藻可以利用阳光的能量将空气中的氮气转化为氨。这个过程被称为固氮。相比之下，化肥的化学生产需要大量的化石燃料，并产生温室气体。该项目将研究鱼腥藻的固氮规律，鱼腥藻是生长、生理和遗传学方面最具特征的蓝藻之一。这个项目的第二个关键目标是让不同的学生成为研究团队的成员，并对他们进行教育和支持。这个项目将包括高中生，特别是来自服务不足的学区的高中生，本科生和研究生，作为研究的积极参与者。鱼腥藻在蓝藻模型系统中是独一无二的，因为它有两个同源的固氮酶系统。其中一种只在有氧生长条件下称为异形胞的特殊厌氧细胞中起作用，而另一种只在厌氧生长的营养细胞中起作用。这项研究将确定控制这些互补固氮酶表达的机制，重点是响应氮胁迫的全球机制。本项目将表征两个主要的激活蛋白CnfR1和CnfR2，它们导致两个固氮酶基因簇在异形胞或营养细胞中的差异表达。此外，这项研究将在系统范围的水平上确定已知的全球应激因子和转录因子在调节这两个固氮酶系统中的作用。采用合成生物学的方法，鱼腥藻的固氮酶基因将在缺乏这种能力的菌株中表达，这是生产“硝化体”的长期目标的一部分，这是一种假想的植物细胞中类似蓝藻的细胞器，可以为植物固定氮素。将固氮酶基因转移到植物上的目标是减少对作物生产中含氮肥料的依赖。这些目标将通过将传统基因技术与合成生物学方法相结合来实现。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Cyanobacteria are ancient microorganisms that were among the first organisms to produce oxygen on earth. Today, cyanobacteria are important organisms in the environment. They get their energy from sunlight, their carbon from carbon dioxide in the air, and their nitrogen from the nitrogen gas in the air. They are important not only as free-living organisms, but also as partners in many symbiotic associations with plants and fungi. The cyanobacterium Anabaena can use the energy from sunlight to convert nitrogen gas in the air to ammonia. This process is called nitrogen fixation. In contrast, chemical production of fertilizer requires large amounts of fossil fuels and produces greenhouse gases. The project will investigate the regulation of nitrogen fixation in Anabaena, one of the best characterized cyanobacteria in terms of growth, physiology and genetics. A second key objective of this project is to involve, educate, and support diverse students as members of the research team. This project will include high school students, especially from underserved school districts, undergraduates and graduate students, working together as active participants in the research.Anabaena is unique in model cyanobacterial systems in that it has two homologous nitrogenase systems. One functions only in specialized anaerobic cells called heterocysts under aerobic growth condition, while the other functions only in anaerobically-grown vegetative cells. This research will determine the mechanisms that control expression of these complementary nitrogenases, focusing on global mechanisms that respond to nitrogen stress. This project will characterize the two primary activator proteins, CnfR1 and CnfR2, which lead to differential expression of the two nitrogenase gene clusters in heterocysts or vegetative cells. Further, the research will determine, at a system-wide level, the role of known global stress factors and transcription factors, in regulation of the two nitrogenase systems. Taking a synthetic biology approach, nitrogenase genes from Anabaena will be expressed in a strain that lacks this capability, as part of the longer term goal of producing a "nitroplast", a hypothetical cyanobacterial-like organelle in a plant cell that could fix nitrogen for the plant. The goal of moving nitrogenase genes to plants is to reduce reliance on nitrogen-containing fertilizers for crop production. These objectives will be achieved by combining traditional genetic techniques with synthetic biology approaches.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.