Genetic Engineering
Since RuBisCO is often rate-limiting for photosynthesis in plants, it may be possible to improve photosynthetic efficiency by modifying RuBisCO genes in plants to increase its catalytic activity and/or decrease the rate of the oxygenation activity. This could improve biosequestration of CO2 and be an important climate change strategy. Approaches that have begun to be investigated include expressing RuBisCO genes from one organism in another organism, increasing the level of expression of RuBisCO subunits, expressing RuBisCO small chains from the chloroplast DNA, and altering RuBisCO genes so as to try to increase specificity for carbon dioxide or otherwise increase the rate of carbon fixation.
One avenue is to introduce RuBisCO variants with naturally high specificity values such as the ones from the red alga Galdieria partita into plants. This might be expected to improve the photosynthetic efficiency of crop plants although possible negative impacts have yet to be studied. Advances in this area include the replacement of the tobacco enzyme with that of the purple photosynthetic bacterium Rhodospirillum rubrum.
A recent theory explores the trade-off between the relative specificity (i.e., ability to favour CO2 fixation over O2 incorporation, which leads to the energy-wasteful process of photorespiration) and the rate at which product is formed. The authors conclude that RuBisCO may actually have evolved to reach a point of 'near-perfection' in many plants (with widely varying substrate availabilities and environmental conditions), reaching a compromise between specificity and rate of reaction.
Since photosynthesis is the single most effective natural regulator of carbon dioxide in the Earth's atmosphere, a biochemical model of RuBisCO reaction is used as the core module of climate change models. Thus, a correct model of this reaction is essential to the basic understanding of the relations and interactions of environmental models. A new theory and model of the biochemical reaction of photosynthesis and the draw-backs of today's most widely used model of photosynthesis is discussed in the new volume of Advances in Photosynthesis and Respiration ( chapter 12).
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