One-step metabolic engineering for genetic improvement of hybrid poplar to increase carbon and nitrogen assimilation, and biomass production
Subhash C. Minocha1, Rakesh Minocha2
1University of New Hampshire, USA
2USDA Forest Service, USA
Abstract: Nitrogen perhaps is the costliest nutrient input into agriculture that often limits carbon uptake in plants, thus restricting their growth and productivity. Also, nitrogen (as NO3) is a major cause of water pollution due to leaching and run-offs. A better understanding of genetic and physiological regulation of N assimilation and nitrogen use efficiency could help us deal with both challenges, particularly in relation to reforestation and management of land for cultivated forestry.
Our research is aimed at testing if genetic manipulation of the core pathway of glutamate-ornithine-polyamines-gamma-aminobutyric acids/proline (that regulates major nitrogen and carbon metabolic interactions) will lead to increased nitrogen use efficiency and higher carbon sequestration in poplar. The primary target of genetic engineering is the metabolism of one of the ubiquitous metabolites in all living organisms (i.e. putrescine (a polyamine). Poplars are of great economic importance for bioenergy production and phytoremediation of heavy metals and organic pollutants.
Our research is focused specifically on a short-rotation hybrid poplar (Populus nigra x maximowiczii-NM6) through genetic manipulation of polyamines, a group of metabolites that are essential for growth and tolerance to drought, freezing, salinity, and oxidative stress among other type of abiotic stresses, and biotic stresses. Additionally, polyamines participate in key molecular and cellular processes mediated by signaling pathways involving gamma-aminobutyric acid, NO, and ethylene. The results show that genetic manipulation of a single step in the polyamine biosynthetic pathway (i.e. ornithine-to-putrescine) in poplar cells and Arabidopsis thaliana plants can lead to increased assimilation of both nitrogen and carbon. Using techniques of genetic engineering, transcriptomics and metabolomics, we found that increased accumulation of putrescine causes a net increase in total carbon and nitrogen accumulation and biomass production in transgenic cells/plants. Furthermore, increased putrescine production does not affect the: (1) content of spermidine and spermine, (2) turnover rates (half-life) of the three major polyamines, (3) expression of a broad spectrum of genes in the Glu-Orn-Put-Spd-Spm-GABA pathway; and (4) production of Put via the Arg pathway. However, many of the genes whose expression is altered are involved in transcription, translation, membrane transport, osmoregulation, shock/stress/wounding, and cell wall metabolism. The most noteworthy metabolic changes are in organic acids, carbohydrates and nitrogen-containing metabolites. The results provide valuable information about the role of polyamines in regulating both nitrogen and carbon assimilation pathways in plants. The results also provide guidance in designing transgenic plants with increased nitrogen use efficiency as well as increased carbon assimilation and biomass production. This approach will contribute to agriculture, forestry and rural life improvements by enhancing sustainable agroforestry as a source of renewable energy.
After receiving Ph.D. from University of Washington, Seattle (1972-1974), Dr. Minocha joined the University of New Hampshire as assistant professor in 1974 where he is currently a professor of Plant Biology and Genetics. During his tenure at UNH, he has been involved in: (1) teaching a variety of courses in Plant Physiology, Plant Developmental Biology, Plant Biotechnology, Biotechnology and Society, Cell Culture, and Plant Growth Regulators; (2) research on a broad range of projects, like cyto differentiation of xylem cells in cell cultures of Jerusalem artichoke, somatic embryogenesis in carrot, tissue culture of a diverse group of plant species; genetic manipulation of plant metabolism using techniques of genomics, transcriptomics and metabolomics; (3) Establishing national and international collaborations in research through sabbatical leaves, and reciprocal visits of scientists and scholars from five continents; (4) Founded and directed various academic and outreach programs; (5) had a very active and productive graduate student, post docs, and visiting scientists mentorship programs; and (6) research supervision of more than 250 undergraduate thesis.
At UNH, Dr. Minocha has received “Excellence in Public Service” award (1995), the “UNH Distinguished Professorship” (2002), and “Excellence in International Engagement Award” (2013). In addition, he has received prestigious international fellowships from the Humboldt Foundation (Germany), the Norwegian Research Council (Norway), the Japanese Society for the Promotion of Science (Japan) and the Transfer of Knowledge through Expatriate Nationals (United Nations through the Government of India). He has about 120 peer-reviewed publications and three (edited) books to his credit.