Next, the team plans to replicate procedures in soybeans, cowpeas (black-eyed peas) and cassava, a tropical root crop that is a staple for more than a billion people around the world. Their goal is to increase the yields and opportunities for farmers worldwide, particularly smallholder farmers in Sub-Saharan Africa and Southeast Asia.
Led by the University of Essex, the team genetically engineered a model crop to overexpress the H-protein that is involved in this recycling process, called photorespiration. Plants such as soybeans and wheat waste between 20 and 50 percent of their energy recycling toxic chemicals created when the enzyme Rubisco—the most prevalent enzyme in the world—grabs oxygen molecules instead of carbon dioxide molecules during photorespiration. Over two years of field trials, researchers found that increasing the Rubisco enzyme in the plants’ leaves increases production 27 to 47 percent. However, increasing it throughout the plant stunts growth and metabolism, resulting in four-week-old plants that are half the size of their unaltered counterparts.
“Plant scientists have traditionally used promoters that express proteins at high levels throughout the plant and there are many examples where this has worked really well,” said the lead author Patricia Lopez-Calcagno, a senior research officer at Essex. “But for the H-protein, more is not always better. Through our work, we discovered that when we translate this method to other plants, we will need to tune our manipulations to the right levels in the right tissues.”
Previous studies manipulated H-protein levels in Arabidopsis, a small model plant used in laboratory experiments. This is the first time that the H-protein has been evaluated in a crop in real-world growing conditions. The team used tobacco, widely considered the lab rat of plant biology because it is easy to genetically engineer and can be quickly grown and tested in outdoor field trials. Once a modification has been proven to be effective in tobacco, the same approach can be applied to food crops that are needed to feed our growing population.
“The reality is that as growing season temperatures continue to increase, the yield hit caused by photorespiration will also increase,” said co-author Paul South, a USDA-ARS postdoctoral researcher in the Carl R. Woese Institute for Genomic Biology at the University of Illinois. “If we can translate this discovery to food crops, we can equip farmers with resilient plants capable of producing more food despite increasing temperature stress.”
To further increase yields, the team plans to combine this trait with others developed by the RIPE project, including a method reported in Science that boosted production by 20 percent by helping plants adapt to fluctuating light levels more quickly.
“Improvements obtained with each individual trait brings us one step closer to meeting the imminent food demands of 2050 and in combination, we believe that we can contribute to this century’s Green Revolution,” said Principal Investigator Christine Raines, a professor of plant molecular physiology at Essex. “We are committed to developing these sustainable technologies as quickly as possible and ensuring that the farmers and communities who need them most have global access.”
The paper “Overexpressing the H-protein of the glycine cleavage system increases biomass yield in glasshouse and field grown transgenic tobacco plants” is available by request. Co-authors also include Stuart Fisk, University of Essex; Kenny Brown, University of Essex; and Simon Bull, Institute of Agricultural Sciences.