The transgenic key to more productive crops

Transgenic tobacco plants engineered with synthetic metabolic pathways designed to bypass the inefficient and costly side effects of natural photorespiration show large increases in productivity - as much as 40% over unmodified tobacco plants, a new study says.

The results suggest a method that could be used to overcome the inherent limitations of natural photosynthesis to improve productivity and yields for other important crops globally, such as rice or wheat. As existing efforts to boost crop yields, like increased use of pesticides, fertilizers and irrigation, are now largely optimized, photosynthetic efficiency is a major focus.

The carbon-fixing enzyme RuBisCO, which is critical in transforming atmospheric carbon dioxide into plant biomass, also reacts with oxygen to produce dysfunctional biproducts. Photorespiration detoxifies these byproducts and converts them into useful molecules.

However, this process comes at a cost of energy lost and it also reduces the photosynthetic efficiency - a key determinant of yield potential - of some of the planet's most important crops by 20-50%. Overcoming the yield penalty imposed by inefficient photorespiratory pathways has the potential to greatly increase crop productivity, an achievement which is necessary if our rapidly growing global agricultural demand is to be met, according to the authors.

Using tobacco as a model crop, Paul South and colleagues introduced non-native and synthetic metabolic pathways that more efficiently recycled the biproducts of RuBisCO oxygenation. Tobacco was used due partly to its ease of genetic manipulation as well as because of its hardy nature and bountiful seed production, which make it well-suited for research purposes.

Building upon previous work, South et al. engineered a transgenic variety of the plant which carried a synthetic glycolate metabolic pathway designed to bypass the regular routes of natural photorespiration.

According to the results of experiments in both greenhouse conditions and in the field under agricultural conditions, the synthetic pathways drove large increases in dry weight biomass. In a Perspective, Marion Eisenhut and Andreas Weber discuss the implications of the study's findings in more detail.