2012 Annual Report
Preliminary experiments with the recombinant enzyme showed that creosote Rubisco activase was inefficient in activating camelina Rubisco, whereas cotton Rubisco activase was an effective activator. Consequently, a revised strategy for improving the thermotolerance of camelina photosynthesis has been adopted involving insertion of the alpha- and beta-isoforms of the more temperature tolerant Rubisco activase from cotton. Based on the temperature response of enzyme activity, Rubisco activase from cotton would increase the thermal stability of camelina photosynthesis by about 5°C. To increase the probability of success, camelina was also transformed with the alpha- and beta-isoforms of Rubisco activase from a wild rice species. This species of Oryza is native to hot, arid regions of northern Australia. Together with Macquarie University in Sydney, the temperature response of photosynthesis and Rubisco activation in this species exhibited considerable heat tolerance. Thus, the Rubisco activase from this species is another potential candidate for improving the thermal tolerance of camelina photosynthesis.
Considerable progress has been made in addressing aspects of the project related to Rubisco activase regulation. Significant differences in the properties of the non-redox regulated forms of Rubisco activase were found among species. The data showed that the beta-isoform of Rubisco activase from Arabidopsis was insensitive to inhibition by physiological ratios of ADP/ATP when not paired with its alpha-isoform, whereas the beta-isoform from tobacco, a species that does not express an alpha-isoform, was acutely sensitive to inhibition by ADP.
To understand the role of regulating Rubisco activase in photosynthesis, photosynthetic induction was measured. In plants like tobacco, that contain a Rubisco activase that is inhibited by physiological ratios of ADP/ATP, the rate of photosynthetic induction was dependent on the duration of low light prior to induction. In contrast, plants that contain a Rubisco activase enzyme that is insensitive to inhibition by ADP exhibited no lag in the induction of CO2 fixation upon transition from low to high light. These data indicate that the sensitivity of Rubisco activase to inhibition by ADP influences the rate of photosynthetic induction. This influence of Rubisco activase is particularly important for carbon gain in environments with highly fluctuating light regimes.
Progress performance on this agreement has been monitored through annual reports to DOE, email correspondence with the Project Manager and semi-annual PI meetings.
The research on improving plant thermotolerance using camelina relates directly to Component 4 of the Action Plan for NP301: Plant Biological and Molecular Processes and specifically to Problem Statement 4B: Biological Processes that Improve Crop Productivity and Quality