Nitrogen is one of the crucial micronutrients for plant growth. Plants take up nitrate and ammonium from soil, which are then assimilated and used for the biosynthesis of nitrogen-containing compounds such as amino acids, proteins, nucleotides, and chlorophyll. The amount of assimilated nitrogen strongly affects plant growth and crop yields, and vast quantities of nitrogen fertilizers are applied to agricultural fields to maximize crop yield. However, plants only take up less than half of applied nitrogen fertilizers, whereas the rest leeches off as a pollutant into subterranean water and rivers, which induces hypertrophication of water bodies. The generation of crops with high nitrogen use efficiency will be crucial for sustainable and oligotrophic agriculture.
Nitrogen assimilation in plants starts with inorganic nitrogen compounds in soil and the 2-oxoglutarate (2-OG) carbon skeleton. As 2-OG is produced by sequential reactions of photoassimilated carbohydrates, enhancing the activity of one enzyme in the sequential process would not be sufficient to increase the 2-OG levels. To increase the 2-OG levels and reveal effects of enhanced 2-OG production on nitrogen assimilation, we generated transgenic Arabidopsis plants by introducing a Dof1 gene that encodes a transcription factor regulating the expression of several genes involved in the 2-OG production pathway. The transgenic plants displayed enhanced nitrogen assimilation and improved growth under low-nitrogen conditions (Proc. Natl. Acad. Sci. USA 101, 7833-7838, 2004). This work was first published in PNAS, and was a news feature in Science, Scientific American, Le Monde (France), and other mass media. We are currently investigating the effect of Dof1 in other plant species, and continue to search for new genes to improve the nitrogen use efficiency in plants.

Publications (selected)

• Ueda Y., Yanagisawa, S. (2017) Engineering nitrogen use effciency with transcription factors, in Engineering Nitrogen Utilization in Crop Plants, (eds.), Springer Science+Business Media LLC, in press.
• Kurai, T., Wakayama, M., Abiko, T., Yanagisawa, S., Aoki, N., Ohsugi, R. (2011) Introduction of ZmDof1 gene into rice enhances carbon and nitrogen assimilation under low nitrogen condition, Plant Biotechnol. J. 9: 826–837.
• Yanagisawa S, Akiyama A, Kisaka H, Uchimiya H, Miwa T. (2004) Metabolic engineering with Dof1 transcription factor in plants: Improved nitrogen assimilation and growth under low nitrogen conditions. Proc. Natl. Acad. Sci. USA, 101, 7833-7838. [Abstract]
• Yanagisawa, S. (2000) Dof1 and Dof2 transcription factors are associated with expression of multiple genes involved in carbon metabolism in maize. Plant J. 21: 281-288. [Abstract]