EAGER: Preventing N2O Emissions by Expressing N2O Reductase in Plant Mitochondria

一氧化二氮(N2O)是一种强有力的大气污染物，通过一种名为原核生物一氧化二氮还原酶(N2OR)的细菌酶来生物去除。在高产农业土壤中，N2OR往往活性不足。因此，N2O在后工业化大气中不断增加，约占目前温室气体辐射强迫的12%。N2O也是一种重要的臭氧消耗化学品。该项目将研究一种新的、具有潜在变革性的农业N2O排放解决方案。N2OR将在植物线粒体中表达，从而持续活跃，从土壤和大气中清除N2O。据报道，在体外缺氧条件下，N2OR在常规转化nosZ的植物提取物中具有活性。nosZ是N2OR的结构基因。利用研究人员在实验室开发的用于构建用于植物修复的新型合成遗传载体的专业知识，他们将表达以氨基酸序列修饰的nosZ，这些氨基酸序列将蛋白质靶向线粒体基质和线粒体内周膜。线粒体是细胞内呼吸减少的部位，即耗氧部位，类似于反硝化细菌中N2O还原的部位。这是一个高风险的项目，但具有巨大的全球重要性的潜在利益。通过一年的资助，该项目试图确定：1.利用现有的nosZ序列和线粒体靶向序列，是否有可能在整个植物中减少N2O；2.nos操纵子中假定的辅助基因nosXDFYL是否对最佳N2OR表达是必需的；以及3.如果能使N2OR在植物中活跃起来，并将这项技术大规模应用于玉米和水稻等作物，预计谷物种植的N2O排放将显著减少，导致N2O增加的突然减少。这种削减有可能以可持续的方式实现，几乎不需要额外的能源支出。这将是温室气体和臭氧消耗排放的一次重大而受欢迎的削减，这是目前IPCC项目没有预料到的。这一奖项反映了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。

Nitrous oxide (N2O) is a potent atmospheric pollutant that is removed biologically by a bacterial enzyme called prokaryotic nitrous oxide reductase (N2OR). In high yield agricultural soils N2OR is often inadequately active. Thus, N2O has been continuously increasing in post-industrial atmosphere, so that it accounts for about 12% of present radiative forcing by greenhouse gases. N2O is also a significant ozone depleting chemical. A novel and potentially transformative solution to agricultural emissions of N2O will be investigated in this project. N2OR will be expressed in plant mitochondria so that it is active continuously, removing N2O from soil and atmosphere. N2OR has been reported to be active under anoxic conditions in vitro in extracts of plants conventionally transformed with nosZ, the structural gene for N2OR. Using the expertise that the investigators have developed in their lab for the construction of novel synthetic genetic vectors for phytoremediation, they will express nosZ modified with the amino acid sequences that target the proteins to the mitochondria matrix and inner periplasmic membrane of the mitochondria. The mitochondrion is the site of respiratory reduction in the cell, i.e., the site of oxygen consumption, and is analogous to the site of N2O reduction in denitrifying bacteria. This is a high-risk project, but with great potential benefits of global importance. With one year of funding, the project seeks to determine:1. whether N2O reduction in whole plants is possible using current nosZ sequences and mitochondrial targeting sequences,2. whether the putative helper genes in the nos operon, nosXDFYL, are necessary for optimal N2OR expression, and3. whether N2OR expressing plants can prevent N2O emissions from fertilized soils.If N2OR can be made to be active in plants and if this technology is applied on a large scale to crops such as maize and rice, it is expected that N2O emissions from grain cultivation could be cut significantly, resulting in a sudden reduction in N2O increases. Potentially this reduction could be accomplished sustainably with little to no additional energy expenditure. This would be a major and welcome cut in greenhouse gas and ozone depleting emissions, unanticipated by present IPCC projections.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.