Rubisco activity and regulation as targets for crop improvement

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 CO(2) and NH(3) 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 CO(2) 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.

Structure-Function Studies with the Unique Hexameric Form II Ribulose-1,5-bisphosphate Carboxylase/Oxygenase (Rubisco) from Rhodopseudomonas palustris

“…The hexameric assembly is consistent with native molecular weight determinations from size exclusion chromatography and static light scattering experiments yielding an approximate molecular mass of 300 kDa. 4 It is thus likely that this quaternary structure arrangement is biologically relevant. The average root mean square deviation between ␣-carbon chains of all the dimers from both structures is 0.318 Å with a range from 0.11 to 0.45 Å.…”

“…There has been much interest in manipulating Rubisco because it is an inefficient biological catalyst, and the carboxylation efficiency of the enzyme is further diminished by its competition with O 2 . With increased potential to use Rubisco and other catalysts for enhancing carbon capture strategies and to engineer autotrophic organisms for biofuel production, it is clear that even small but incremental additions to knowledge about the catalytic mechanism of this enzyme may have a significant impact (4,5).…”

“…Using random mutagenesis, a second-site suppressor was isolated for a negative mutant using a previously described biological selection system (23). The structure-function analyses presented here help in better understanding the structural basis for catalysis in form II Rubisco, and these studies might prove useful for engineering a Rubisco with optimized properties for a variety of applications (4,5).…”

Transplastomic plants for innovations in agriculture. A review

“…These data clearly show that (1) a better understanding of factors regulating RuBisCO assembly and activity, (2) potential co-integration with other biotechnological strategies to improve photosynthetic carbon assimilation, and (3) novel methods and further efforts are needed to achieve beneficial changes in RuBisCO activity via genetic engineering which has been restricted until now by the very complex catalytic chemistry and high level expression of the enzyme (Whitney et al 2011a;Parry et al 2013).…”

“…The catalytic activity of RuBisCO is slow and inefficient because it is limited by several factors including different CO 2 and O 2 concentrations, high light intensity, etc., and it also considerably varies among the different organisms. Therefore, successful manipulation of the kinetics and regulation of RuBisCO offers a promising target for genetic engineering to improve crop photosynthesis, productivity, and yield, especially under changing environmental conditions such as increasing CO 2 levels and temperature, and limited water and nitrogen supply Whitney et al 2011a;Hanson et al 2013;Parry et al 2013).…”