Almost every living creature on Earth relies on photosynthesis for its survival, but the process is far from efficient. Now some clever genetic engineering that gets around one of the process's stumbling blocks has been shown to boost crop productivity by 40 percent in the field. The world is crying out for these kinds of transformative gains. The Green Revolution of the 1960s saw global crop yields rise dramatically as fertilizers, pesticides, and industrial agriculture became widespread. But we've more or less optimized these methods, and current productivity improvements are ticking up at around two percent per year.
The enzyme ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) is one of the most abundant proteins on Earth. During photosynthesis, it assimilates atmospheric CO2 into biomass and hence is a major driver of the global carbon cycle. However, the enzyme is catalytically imperfect. It accepts not only CO2 as a substrate, but also O2, which leads to the formation of a toxic byproduct, 2-phosphoglycolate (2-PGlycolate) (1). The metabolic pathway photorespiration detoxifies 2-PGlycolate, and it is essential for performing photosynthesis in an O2-containing atmosphere.
Biological carbon fixation requires several enzymes to turn CO2 into biomass. Although this pathway evolved in plants, algae, and microorganisms over billions of years, many reactions and enzymes could aid in the production of desired chemical products instead of biomass. Schwander et al. constructed an optimized synthetic carbon fixation pathway in vitro by using 17 enzymes--including three engineered enzymes--from nine different organisms across all three domains of life (see the Perspective by Gong and Li). The pathway is up to five times more efficient than the in vivo rates of the most common natural carbon fixation pathway. Further optimization of this and other metabolic pathways by using similar approaches may lead to a host of biotechnological applications.
Atmospheric carbon dioxide levels are rising, triggering global climate change, scientists agree. Researchers have been searching for ways to scrub some of this damaging gas from the atmosphere, and the answer may have been right in front of them. "We actually have taken our inspiration from nature itself," says Tobias Erb, a biochemist at the Max Planck Institute for Terrestrial Microbiology in Germany, in a phone interview with The Christian Science Monitor. Plants and other photosynthesizing organisms can turn carbon dioxide into biomass. And now Dr. Erb and his team have built a synthetic pathway to do that more efficiently – at least in a test tube, and perhaps someday in plants or other organisms.
Wolf and Ziska suggest that soil and species attributes can explain an unexpected 20-year reversal of C3-C4 grass responses to elevated CO2. This is consistent with our original interpretation; however, we disagree with the assertion that such explanations somehow render our results irrelevant for questioning a long-standing paradigm of plant response to CO2 based on C3-C4 differences in photosynthetic pathway. In a thoughtful consideration of the mechanisms responsible for the unexpected reversal of C3 versus C4 grass community responses to elevated CO2 observed over a 20-year period (1), Wolf and Ziska (2) make many excellent points. However, they inaccurately represent the interpretations and conclusions of our paper, include at least one key factual error, and come to several conclusions that we believe the evidence does not support. The thesis of Wolf and Ziska is that our results (1) can be explained by considering the natural history of the experimental plants and soils "…without challenging general expectations of C3 and C4 grass responses to elevated CO2 in the absence of other limitations."