Dr Robert Sharwood, Australian National University
Prospects for improving photosynthesis in food and fiber under future climates
The uncertainty of future climate change and the continued reductions in arable land are placing significant pressures on cropping systems to maintain annual increases in productive yield. To mitigate future climates and the increasing threat towards global food security, new solutions to manipulate photosynthesis are required. One crucial enzyme in this process is Rubisco (Ribulose-1,5-bisphosphate carboxylase /oxygenase), which catalyses the rate-limiting step of CO2 fixation of substrate RuBP (ribulose-1,5-bisphosphate carboxylase/oxygenase. The carboxylation of RuBP and the subsequent cycling of the catalytic product 3-phosphoglycerate through the Calvin cycle provides the carbohydrate building blocks for maintaining plant growth and crucial for yield potential. Remarkably, Rubisco is a bifunctional enzyme that often confuses its substrate CO2 with O2 and suffers from numerous catalytic imperfections. These include a slow catalytic turnover rate (2–4 turnovers per second in C3 plants), low affinity for substrate CO2 (KmCO2) and a poor specificity for CO2 as opposed to O2. To circumvent these catalytic inefficiencies, C3 plants invest significant resources into Rubisco synthesis and can constitute up to 50% of total soluble leaf protein to maintain a suitable CO2 assimilation rate. My lab focuses on improving the catalytic properties of Rubisco from food and fiber crops by interrogating the catalytic properties of naturally occurring forms from photosynthetic organisms and to engineer improved Rubisco into higher plants through chloroplast transformation. This talk will focus on the prospects for improving photosynthetic CO2 assimilation to cope better to future climate extremes through tailoring Rubisco catalysis to these variable climates.