Optimizing Rubisco and its regulation for greater resource use efficiency

Abstract

Rubisco catalyses the carboxylation of ribulose-1,5-bisphosphate (RuBP), enabling net CO2 assimilation in photosynthesis. The properties and regulation of Rubisco are not optimal for biomass production in current and projected future environments. Rubisco is relatively inefficient, and large amounts of the enzyme are needed to support photosynthesis, requiring large investments in nitrogen. The competing oxygenation of RuBP by Rubisco decreases photosynthetic efficiency. Additionally, Rubisco is inhibited by some sugar phosphates and depends upon interaction with Rubisco activase (Rca) to be reactivated. Rca activity is modulated by the chloroplast redox status and ADP/ATP ratios, thereby mediating Rubisco activation and photosynthetic induction in response to irradiance. The extreme thermal sensitivity of Rca compromises net CO2 assimilation at moderately high temperatures. Given its central role in carbon assimilation, the improvement of Rubisco function and regulation is tightly linked with irradiance, nitrogen and water use efficiencies. Although past attempts have had limited success, novel technologies and an expanding knowledge base make the challenge of improving Rubisco activity in crops an achievable goal. Strategies to optimize Rubisco and its regulation are addressed in relation to their potential to improve crop resource use efficiency and climate resilience of photosynthesis.

Surveying Rubisco diversity and temperature response to improve crop photosynthetic efficiency

“…A large number of studies have previously described Rubisco catalysis (for review, see Parry et al, 2007Parry et al, , 2013Whitney et al, 2011b;Carmo-Silva et al, 2015). However, this still represents a very small fraction of known lands plants (approximately 0.2% based on current literature).…”

“…Potential unintended effects on assembly could be a factor when mutating residues known to be involved in interactions between the large and small subunits. Careful consideration must also be given to avoiding effects on holoenzyme assembly and compatibility with ancillary proteins or assembly chaperones (Carmo-Silva et al, 2015;Whitney et al, 2015). This presents a promising avenue for future work in model systems, testing these residues either singly or in combination, with previous studies having shown strong potential for modifying Rubisco catalysis with targeted amino acid substitutions (Whitney et al, 2011b).…”

“…Previous characterization of Rubisco from a limited number of species has not only demonstrated significant differences in the underlying catalytic parameters, but also suggests that further undiscovered diversity exists in nature and that the properties of some of these enzymes could be beneficial if present in crop plants (Carmo-Silva et al, 2015). Recent studies clearly illustrate the variation possible among even closely related species (Galmés et al, 2005(Galmés et al, , 2014b(Galmés et al, , 2014cKubien et al, 2008;Andralojc et al, 2014;Prins et al, 2016).…”

“…In addition, the ability to coanalyze catalytic properties and DNA or amino acid sequence provides the opportunity to correlate sequence and biochemistry to inform engineering studies (Christin et al, 2008;Kapralov et al, 2011;Rosnow et al, 2015). While the amount of gene sequence information available grows rapidly with improving technology, knowledge of the corresponding biochemical variation resulting has yet to be determined (Cousins et al, 2010;Carmo-Silva et al, 2015;Sharwood and Whitney, 2014;Nunes-Nesi et al, 2016).…”

Crops, Nitrogen, Water: Are Legumes Friend, Foe, or Misunderstood Ally?

“…In a review of resource use efficiency and climate resilience, Carmo-Silva et al [103] noted that a negative relationship between Rubisco activase and Rubisco content could cancel out potential benefits for WUE of additional allocation of N to the latter. At a molecular level, and in the absence of considerations of N, drought downregulates many photosynthesis-related genes, possibly enhancing WUE i and aiding survival via a slowing of growth [104].…”