Assessing the effects of genetic modifications on photosynthetic capacity in Nicotiana tabacum (tobacco) and Glycine max (soybean)

The global population is projected to exceed nine billion people by the year 2050, which means an ever-increasing strain on the world’s natural resources, especially food, fuel, and fiber. The challenge comes with trying to produce more food crops on the same amount of land while maintaining or lessening the amount of inputs, including water and fertilizer. One avenue for meeting this demand is to engineer increased photosynthetic conversion efficiency to in turn increase genetic yield potential, which is defined as the maximum amount of yield a plant can produce in optimal growing conditions based on genetics. This study assesses the resulting plants from two different approaches to increase photosynthetic conversion efficiency. The first approach explores five transformations of Nicotiana tabacum cv. Petite Havana. Three of the transformations encode different changes in the binding specificity of ribulose-1,5-bisphosphate carboxylase/oxygenase for carbon dioxide, one encodes a gene for expression of a bicarbonate transporter, and one overexpresses the native rubisco by 15%. Plants were phenotyped in an agricultural field trial and then in two controlled environment experiments. It was predicted that these modifications would increase rubisco-limited photosynthesis. No comparisons made between wild type tobacco and the modified tobacco types were shown to be significantly better in the modified tobacco types. For this reason, determining the rubisco activation rates of the lines that have an altered binding specificity for CO2 at a range of temperatures would inform how these changes are altering rubisco kinetics on a molecular scale and could inform future decisions about modifications to rubisco. The second approach explores two transformations of Glycine max cv. Thorne. One transformation encodes a cyanobacterial gene that affects carbon dioxide concentrations around rubisco and the other encodes a cyanobacterial gene fructose-1,6-bisphosphate/sedoheptulose-bisphosphatase. Plants were examined in two controlled environment experiments in addition to an agricultural field trial. This approach has multiple predictions. 1) Expressing the ictB gene increases rates of rubisco-limited photosynthesis and RuBP regeneration-limited photosynthesis. 2) Expressing the SBFB gene will show significantly increased RuBP regeneration-limited photosynthesis. No comparisons made between wild type soybean and the modified soybean types were shown to be significantly better in the modified soybeans. In the cases of ictB and SBFB genes, it would be beneficial to elucidate their functions in cyanobacteria before transforming them into higher plants again. Fully understanding their function and mechanism would allow for the optimization of introducing such cyanobacterial genes into higher plants. Though the genetic alterations made to the plants in this study did not have the predicted outcomes based on previous research, this study has potentially contributed to the knowledge of which genes do and do not have strong impacts on photosynthetic capacity and efficiency