A new study published on 8 November in Nature Communications has demonstrated that modifying the signalling of the plant steroids, known as brassinosteroids, in only the vascular tissue of plants can effectively increase drought resistance without sacrificing growth.
Decreases in rainfall and abnormally high temperatures across northern and eastern Europe have led to huge losses in cereals and potato crops, as well as other important crops. Thus, it has become increasingly evident that to ensure food security, plant varieties that are productive in drought conditions will be required. This is the first study to present a successful strategy for increased drought resistance without affecting the growth and development of a genetically modified plant.
The international team of researchers from Europe, the United States, and Japan, led by Ana Caño-Delgado from the Center for Research in Agricultural Genomics (CRAG) in Barcelona, Spain, focused on a group of plant steroids known as brassinosteroids that regulate plant development and growth. The so-called phytohormones are known to bind to cell membrane receptors resulting in a signalling cascade that can produce various effects, such as cell elongation and division. Previous attempts to infer drought-resistance on plants by modifying brassinosteroid signalling have been somewhat successful, however, owing to the important influence of these hormones on growth, have always led to much smaller plants.
This latest study investigated mutations of different brassinosteroid receptors in Arabidopsis thaliana (thale cress or mouse-ear cress), a small flowering plant widely used as a model organism in plant biology studies. The researchers discovered the over-expression of BRL3, a brassinosteroid receptor in vascular tissue, leads to increased resistance to water scarcity and importantly, unlike the other mutants, does not cause development and growth defects.
The team also analyzed the metabolites in the genetically modified plants and showed that BRL3 overexpression prepares the plant to respond to drought conditions via a mechanism known as priming ― under normal irrigation conditions, plants overexpressing the BRL3 receptor produce more osmoprotective metabolites (sugars and proline) in the aerial parts and in the roots. Then when exposed to drought conditions, these protective metabolites rapidly accumulate in the roots, thereby protecting the plant from drying out.
Thus far the results have only been demonstrated in a model plant, however, the team is currently focusing on applying the technique to important crops, such as cereals. The findings will hopefully contribute to ensuring global food security in the future. This research is part of a growing body of work seeking to develop more robust crops that can better withstand the potentially catastrophic effects of climate challenges. Another paper published last month showed that naturally occurring epigenetic variation ― changes caused by modified gene expression that do not involve changes in the underlying genetic sequence― in Arabidopsis thaliana can also contribute to rapid adaptive responses (2).
It is becoming increasingly clear that a combination of novel strategies will be necessary to feed the growing global population. Perhaps, subtle changes in gene expression could be used to produce climate-resistant crops, while selective breeding could be used to produce crops that can quickly and naturally adapt to environmental challenges through epigenetic mechanisms.
(1) Fàbregas, N. et al. Overexpression of the vascular brassinosteroid receptor BRL3 confers drought resistance without penalizing plant growth. Nature Communications (2018). DOI: 10.1038/s41467-018-06861-3
(2) Schmid, M.W. et al. Contribution of epigenetic variation to adaptation in Arabidopsis. Nature Communications (2018). DOI: 10.1038/s41467-018-06932-5.
Image: Arabidopsis thaliana, Getty Images.