Genetics and Genomics of Nodulation and Symbiotic Nitrogen Fixation

Abstract

‘Nitrogen’ is critical for plant productivity because of its involvement in proteins, nucleic acids and secondary metabolism. Plants are the major conduit of nitrogen assimilation into the biosphere and achieve this feat through either assimilation of mineral nitrate or biological nitrogen fixation in symbiotic structures called root nodules. The recent discovery of key genes controlling nodule initiation, nodule proliferation and plant defence now provides the opportunity to improve legumes, thereby decreasing the demands on fossil‐fuel based nitrogen fertiliser. The understanding of symbiotic nitrogen fixation led to the recognition that many of the developmental pathways are either shared or pirated from other pre‐existing regulatory mechanisms. Increasingly sustainable agricultural practices based on reduced inputs and ‘triple bottom‐line’ accounting may result. In the near future we may even hope to see the expansion of the nitrogen fixing symbiosis by either transgenic manipulation or ‘smart breeding’ to new crop species.