Field trials to phenotype transgenic tobacco plants with improved RuBP regeneration

Evidence has accumulated indicating that improving photosynthetic capacity can lead to increase in yield. The aims of this project were firstly to produce and identify homozygous transgenic tobacco plants and then to test these plants in field conditions for improved photosynthesis and yield. Transgenic Nicotiana tabacum plants were produced using gene constructs designed to either overexpress the native H-protein of the glycine cleavage system or express the foreign genes for the cyanobacterial bifunctional FBPase/SBPase and algal cytochrome c6 proteins. The bifunctional FBPase/SBPase protein catalyses two steps in the regenerative phase of the Calvin-Benson-Bassham cycle. The H-protein upregulates the complex that facilitates the conversion of glycine to serine in the photorespiratory pathway, while the cytochrome c6 protein is an electron transport protein that assists the flow of electrons from the cytochrome b6f complex to photosystem I. These plants were tested in field conditions as single, double (bifunctional FBPase/SBPase + cytochrome c6) and triple (bifunctional FBPase/SBPase + cytochrome c6 + H-protein) gene manipulations. To determine if the transgenic plants had an increase in productivity over the wildtype and whether combining manipulations could lead to an additive/synergistic increase in productivity. A preliminary trial was held, that targeted single manipulations, which demonstrated significant increases in biomass over the control plants of between 25 to 40%. Due to these results, fully replicated trials were held 2017 and 2018 seasons, where single, the double and triple manipulations were trialled in unison. The 2017 field trials provided maximum increases in biomass of 8% for the single manipulations whereas this was around 18% for the double and triple manipulation. This data provided the strongest evidence that multiple manipulations have a increased effect on growth and productivity than single manipulations. The next stage is to test these manipulations in crop plants and in a range of environmental conditions.