Advancing Our Understanding and Capacity to Engineer Nature’s CO2-Sequestering Enzyme, Rubisco  

Abstract

There is a growing impetus in developing novel strategies to address global concerns regarding food security. As crop productivity gains through traditional breeding begin to lag and arable land becomes scarcer, it seems that we are heading for unsustainable global populations. It has been foreshadowed that global food production will need to rise more than 50% before 2050 to meet the ever-increasing demand. Compounding the problem are the uncertainties of climate change and its impact on agriculture. Strategies to improve crop yield potential have begun to examine aspects of supercharging photosynthesis to drive a new "green revolution." Central to many of these strategies is addressing the limitation of nature's CO 2 -fixing enzyme, Rubisco.The catalytic incorporation of CO 2 into ribulose 1,5-bisphosphate (RuBP) by Rubisco is the first step in the production of carbohydrates by plants, which are used to build biomass and produce energy during growth and development. Despite the pivotal role of Rubisco in linking the inorganic (CO 2 ) and the organic (biomass) phases of the global carbon cycle, it is a slow and confused catalyst, limiting productivity and resource (e.g. water and nutrients) use efficiency in many plants (Long et al., 2006). Understandably, Rubisco has been studied intensively and is a prime target for genetic engineering to improve photosynthetic efficiency (Raines, 2006;Parry et al., 2007). Although the challenge of making a "better Rubisco" has exceeded the grasp and career of many scientists, recent advances indicate that it is not insurmountable. Here, we examine conceptual and technological breakthroughs over the last decade that have identified new and unconventional members of the Rubisco family, revealed molecular aspects of Rubisco biogenesis in plastids and cyanobacteria, advanced our understanding of its catalytic chemistry, and widened our appreciation of the challenges we face to improve Rubisco activity and plant productivity.

Rubisco small-subunit α-helices control pyrenoid formation inChlamydomonas

“…36 and 37), the link between Rubisco molecular structure, aggregation, and pyrenoid function had not previously been proven. In evolutionary terms, there is an inverse relationship between Rubisco specificity and the activity of a CCM in cyanobacteria, chlorophyte algae, and higher plants (38). C 3 plants, and green algae without a CCM (39) or reliant on CO 2 diffusion, have a Rubisco with high specificity for CO 2 (Ω ∼ 80-100).…”

Functional Incorporation of Sorghum Small Subunit Increases the Catalytic Turnover Rate of Rubisco in Transgenic Rice

“…Many attempts to improve photosynthetic efficiency by engineering Rubisco have gained little progress (Andrews and Whitney, 2003;Whitney et al, 2011). Most of these efforts were focused on altering the CO 2 /O 2 specificity of Rubisco to suppress photorespiration.…”

Isoleucine 309 acts as a C 4 catalytic switch that increases ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) carboxylation rate in Flaveria

“…These approaches include elevating the CO 2 concentration within chloroplasts using recombinant CO 2 /HCO 3 − transporters from cyanobacteria or engineering alternative pathways to bypass photorespiration and release CO 2 within the stroma (13,14). Although each strategy faces continuous challenges in its fine tuning and integration into crops, further improvements in yield and in the efficiency of water and nitrogen use are likely by concurrently "speeding up" rubisco (9).…”