Investigating the Role of RAP2.12 and GAPDH in Photosynthetic CO2 Fixation to Improve Drought Tolerance

Manipulation of photosynthetic processes offers an opportunity to increase food production in plants. Current and previous studies have shown that various efforts have been made towards manipulation of photosynthesis to increase crop yield. VBSSM Modelling has been used to identify critical genes involved in the regulation of photosynthetic carbon assimilation. Three highly connected genes were identified as being important in influencing drought-induced transcriptional responses of the genes that encode for enzymes of the Calvin cycle. These genes are the drought-inducible transcription factor RAP2.12, the Calvin cycle gene GAPA-2 and a putative transcription factor (At1g16750) (Bechtold et al., 2016). The first objective was to investigate this model prediction and to determine if GAPA-2 and RAP2.12 are playing essential roles in the regulation of Calvin cycle enzymes under drought and non-drought condition. The single and double mutant lines of RAP2.12 with OE GAPA-2 showed highly variable, and there is no significant difference in growth analyses. Furthermore, it is evident that in the RAP2.12 mutant that the expression of the Calvin cycle genes is altered, predominately under drought stress conditions. Although these changes were not exactly as expected by the modelling these data provide new information on this gene network. Moreover, it has been revealed that the relative amounts of GAPDH plastids subunit (A2B2) and (A4) vary between species, but almost always the A2B2 form is predominant (Howard et al., 2011b). Previously, plants without A4 have been recognised, but no plants without A2B2 have been identified. The second hypothesis was to study the role of GAPB subunit in determining the photosynthetic rate in plants. Arabidopsis and tobacco plants with reduced the protein level of GAPA and GAPB were produced. Transgenic Arabidopsis lines of GAPA and GAPB showed a significant decrease in leaf number and rosette dry weight together with a reduction in photosynthetic capacity.