A UK research collaboration has made advances in plant science which could ultimately pave the way for more nutrient-efficient cereal crops.
The project, which was carried out between the Universities of Oxford and Cambridge, has developed a novel synthetic plant-microbe signalling system that ultimately could provide the foundation for engineering nitrogen fixation in cereal crops.
The team of plant scientists, microbiologists and chemists used synthetic biology techniques to design and then engineer a molecular dialogue between plants and the bacteria surrounding their roots in a zone called the rhizosphere.
It could be a major benefit for non-legume crops like wheat and maize.
Enhancing the root microbiota has enormous potential for improving crop yields in nutrient-poor soils and reducing chemical fertiliser use.
Joint lead author, Dr. Barney Geddes, from Oxford’s Department of Plant Sciences, said: “Plants influence the microbiota of their rhizosphere by sending out chemical signals that attract or suppress specific microbes.
Engineering cereal plants to produce a signal to communicate with and control the bacteria on their roots could potentially enable them to take advantage of the growth-promoting services of those bacteria, including nitrogen fixation.
“To do this, we selected a group of compounds normally produced by bacteria in legume nodules, called rhizopines.
First, we had to discover the natural biosynthetic pathway for rhizopine production, and then design a synthetic pathway that was more readily transferred to plants.
“We were able to transfer the synthetic signalling pathway to a number of plants, including cereals, and engineer a response by rhizosphere bacteria to rhizopine.”
Joint lead author, Dr. Amelie Joffrin, at Oxford developed a new stereoselective synthesis of key rhizopine.
She said: “The synthetic chemistry was essential to provide compounds that enabled the investigation of rhizopine biosynthesis and its transfer from bacteria to plant.
“In particular, the rhizopines produced allowed us to confirm which was the naturally active enantiomer (“hand”) of a key bioactive compound.’
Dr. Ponraj Paramasivan, joint lead author at Cambridge’s Sainsbury Laboratory, explained how the team transferred the rhizopine synthesis genes into barley to assess whether they could engineer rhizopine synthesis in cereals.
She said: ‘We confirmed the barley synthesised and then exuded rhizopine to its rhizosphere.
“We then measured the signalling between barley roots and rhizosphere bacteria and found a significant level of communication was occurring.
These results mean that we could potentially use this signalling pathway to activate root microbiota to fix nitrogen, and a host of other plant growth-promoting services, such as producing antibiotics or hormones or solubilising soil nutrients.
Dr. Paramasivan explained that this technology even has benefits over traditional fertilising methods.
“Weeds currently benefit just as much as the target crop from the application of chemical fertilisers.
“Whereas, a key advantage of this synthetic signalling pathway is that only the specific crop plant that is engineered to produce the signal will benefit.”
Future work in the Poole, Oldroyd and Conway laboratories will focus on how plants can control key processes in root bacteria such as nitrogen fixation, phosphate solubilisation and plant growth promotion.
This opens opportunities to control the bacterial microbiome and its diverse metabolism in cereals. It is likely to be a key component in attempts to engineer nitrogen fixation into cereals.
