The catalytic conversion of carbon dioxide and water to sugar and oxygen is arguably the most important chemical reaction in the world, and one of the oldest. It is so old, in fact, that it evolved when the world’s atmosphere was much lower in oxygen than it is today. So, in a way, photosynthesis is its own worst enemy. Thousands of millions of years later, most modern plants struggle to photosynthesize because of all the darned oxygen in the air — oxygen that they helped to put there. These plants simply cannot distinguish between molecules of carbon dioxide and molecules of oxygen, so they waste their time and energy grabbing both.
Some plants can do better — for example, plenty of weeds (ever wondered why they grow so fast?) have evolved ways to concentrate carbon dioxide inside their leaves, to supercharge their photosynthesis. Cyanobacteria can do this too. But the majority of plants, including most of the crops we rely on for food, have developed a blunter strategy: produce lots and lots of the enzyme that drives the reaction. That enzyme, Rubisco, is thus among the most abundant proteins on the planet.
A significant amount of Rubisco still wastes its time grabbing useless oxygen — reducing the overall efficiency of global photosynthesis by almost one-third. When they discuss ways to boost the world’s food supplies, plenty of plant scientists see leaves’ wasted photosynthesis capacity as, well, low-hanging fruit.
What if crops could borrow the faster-acting Rubisco system of weeds and cyanobacteria? In theory, this would dramatically boost their growth rate and so their yield, all without needing any extra farmland. The appeal of such a strategy is obvious, particularly in the face of the often-quoted United Nations demand for global food production to double by 2050.
In practice, replacing the enzyme has proved difficult. But there is encouraging news: on Nature’s website, researchers report that they have made tobacco plants that use the Rubisco from a cyanobacterium (M. T. Lin et al. Nature http://dx.doi.org/10.1038/nature13776; 2014). Sure enough, the transformed plants photosynthesize faster and have higher rates of CO2 turnover than their conventional counterparts. Faster-growing tobacco plants might not sound like a boon for global welfare, but they do demonstrate what might be possible in future. (Tobacco is a common model organism for genetic-engineering research.)
As biologists Dean Price and Susan Howitt write in an accompanying News & Views (G. D. Price and S. M. Howitt Nature http://dx.doi.org/10.1038/nature13749; 2014): “The work is a milestone on the road to boosting plant efficiency. The advance can be likened to having a new engine block in place in a high-performance car engine — now we just need the turbocharger fitted and tuned.” Available in any colour you like, as long as it’s green.
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