Rubisco activity and regulation as targets for crop improvement

Authors: PARRY, MARTIN - Rothamsted Research; ANDRALOJC, P - Rothamsted Research; SCALES, JOANNA - Rothamsted Research; Salvucci, Michael; Carmo Silva, Ana; ALONSO, HERNAN - Australian National University; WHITNEY, SPENCER - Australian National University

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2012
Publication Date: 11/16/2012
Citation: Parry, M.A., Andralojc, P.J., Scales, J.C., Salvucci, M.E., Do Carmo Silva, A., Alonso, H., Whitney, S. 2012. Rubisco activity and regulation as targets for crop improvement. Journal of Experimental Botany. 64(3):717-730.

Interpretive Summary: In the process of photosynthesis, plants convert light into chemical energy. The energy produced by photosynthesis is then used to synthesize sugars and other foodstuffs from atmospheric carbon dioxide (CO2). To meet the nutritional and energy needs of growing world population, greater plant productivity is needed. However, the yields of the major grain crops are rapidly approaching a plateau and further increases through conventional breeding are unlikely, particularly as the plant warms and episodes of heat stress impair photosynthetic performance. Thus, new strategies are needed to increase the productivity of major crop plants in the face of climate change. The most obvious strategy is to improve the efficiency of photosynthesis by removing certain bottlenecks that limit how much CO2 is taken up by plants. This authoritative review article discusses how ribulose-1,5-bisphospahte carboxylase/oxygenase (Rubisco), the rate-limiting enzyme in photosynthesis, represents an important target that if improved would increase photosynthetic carbon uptake. The article describes the progress made thus far and the challenges that lie ahead in the various strategies for improving Rubisco. The article highlights the tremendous gains in crop productivity, and water- and nitrogen use efficiencies that would be realized from improving Rubisco.

Technical Abstract: Rubisco (ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase) enables net carbon fixation through the carboxylation of RuBP. However, some characteristics of Rubisco make it surprisingly inefficient and compromise photosynthetic productivity. For example, Rubisco catalyses a wasteful reaction with oxygen that leads to the release of previously fixed CO2 and NH3, and the consumption of energy, during photorespiration. Furthermore, Rubisco is slow and large amounts are needed to support adequate photosynthetic rates. Consequently, Rubisco has been studied intensively as a prime target for manipulations to 'supercharge' photosynthesis and improve both productivity and resource use efficiency. The catalytic properties of Rubiscos from diverse sources vary considerably, suggesting that changes in turnover rate, affinity or specificity for CO2 can be introduced to improve Rubisco performance in specific crops and environments. While attempts to manipulate plant Rubisco by nuclear transformation have had limited success, modifying its catalysis by targeted changes to its catalytic large subunit via chloroplast transformation have been much more successful. However, this technique is still in need of development for most major food crops including maize, wheat and rice. Other bioengineering approaches for improving Rubisco performance include improving the activity of its ancillary protein, Rubisco activase, in addition to modulating the synthesis and degradation of Rubisco’s inhibitory sugar phosphate ligands. As the rate-limiting step in carbon assimilation, even modest improvements in the overall performance of Rubisco pose a viable pathway for obtaining significant gains in plant yield, particularly under stressful environmental conditions.