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Drought is a major cause of crop losses worldwide. The main underlying mechanism of plant response to drought stress is already known, and drought-resistance genes have been engineered into crop plants. However, since these drought-resistant crops have low yields, there is an urgent need for novel approaches to producing high-yielding, drought-resistant crops.
As a result of the EU-funded IDRICA project, for the first time, researchers have succeeded in engineering plants with enhanced drought-resistance without adversely affecting growth. The key innovation was not to engineer plants with drought-resistance genes but to modify the signalling process for a group of plant hormones called brassinosteroids.
‘This really was an astonishing finding because normally when you make plants resistant to any stress, the first thing they do when they encounter stress is to stop growing. We were able to break this coupling between resistance to drought and arrested growth by manipulating cell signalling in vascular cells,’ explains Ana Caño-Delgado, CSIC Associate Professor at the Centre for Research in Agricultural Genomics (CRAG) in Spain.
Ignoring stress
The first part of the project focused on understanding drought-resistance in plants at the molecular level. Plant brassinosteroids, first discovered in brassicas, are important regulators of plant growth and development. Over the past 20-30 years, research on the plant Arabidopsis thaliana has revealed how these plant hormones bind to different cell-surface receptors, stimulating signals which pass through the cell to instruct the nucleus to make the proteins needed for growth and development.
‘At the time of the grant application, we were beginning to discover how these hormones act on cell-specific components,’ Caño-Delgado continues. ‘We raised the hypothesis that we could engineer cell-specific signalling to make plants more resilient to stresses.’
At the same time, the project team also filed a patent, based on their initial work with Arabidopsis, for a new process to make plants resistant to drought without penalising growth.
They have recently published a paper in Nature Communications on how they modified signalling in vascular cells. ‘It is like playing a trick on the plants; basically, we are hacking the system that responds to stress so plants don’t realise that there is stress. The plants are even moving more sugars and osmoprotective compounds through vascular cells in a more efficient manner than usual,’ says Caño-Delgado.
During trials, Arabidopsis plants were grown under severe drought conditions for two weeks. The modified plants did not exhibit typical drought responses and continued to grow. Therefore, by simply modifying brassinosteroid signalling locally in the vascular system, the IDRICA researchers obtained drought-resistant plants without affecting their growth.
Agricultural applications
‘The second part of the ERC grant is bringing these findings to agriculture,’ Caño-Delgado explains. ‘We have chosen sorghum as a model cereal. The most important crop losses caused by drought are in cereals, and sorghum is very amenable to work with in the lab.’
Sorghum already has enhanced drought-resistance compared to other cereals, is a staple crop in arid parts of Africa and India, and is regarded as a vanguard cereal under drought conditions exacerbated by climate change.
The project is using gene-editing techniques that modify plant steroid signalling to make drought-resistant sorghum. In future, the approach will be extended to wheat and other crops. It is also applicable to other types of stress, such as plant pathogens.
Caño-Delgado describes this cell-specific engineering strategy as an important step in modernising agriculture to find solutions to food security challenges. She suggests that the focus on single cells is going to be increasingly important in tackling responses to environmental change in agriculture in the future.
‘My grant is a good example of how fundamental academic research supported by Horizon 2020 can provide solutions in the short term,’ she says. ‘I think this is a new frontier for agriculture.’