Scientists unveil key genetic mechanism that improves drought tolerance in Sorghum

A team of researchers from the Centre for Research in Agricultural Genomics (CRAG) has made an exciting breakthrough that could significantly improve drought resistance in crops. By studying sorghum, a cereal widely grown in semi-arid regions, the researchers have identified a molecular mechanism that enables the plant to thrive under water-scarce conditions. This discovery could pave the way for developing more resilient crops to help secure global food supplies in the face of increasing climate crisis.

Sorghum is a vital crop for millions of people living in regions prone to drought, such as Saharan regions of Africa, Southeast Asia, and Central America. While sorghum is naturally more drought-resistant than other cereals, extreme droughts still cause considerable reductions in yield. To address this issue, the CRAG-led research team has focused on understanding how plants respond to drought at a molecular level, identifying key genes that could be modified to boost drought resilience.

The research, led by Ana I. Caño-Delgado, CSIC researcher at CRAG, and published in the Plant Biotechnology Journal, focuses on the plant steroid hormones called brassinosteroids and their receptor BRASSINOSTEROID-INSENSITIVE 1 (BRI1). Brassinosteroids are critical for plant growth, but their role in drought adaptation has remained unclear. The team has now discovered that by modifying in the BRI1 receptor of sorghum (known as SbBRI1), sorghum plants can significantly improve their drought tolerance.

Understanding the response of plants to drought

The team’s study reveals that the SbBRI1 receptor plays a dual role. Under normal conditions, it regulates lignin biosynthesis through a downstream protein called SbBES1. Lignin is a critical component in cell wall formation, but it also requires significant energy and resources. However, during drought conditions, this process changes. The SbBES1 protein becomes less active, and the plant switches to a different metabolic pathway that activates flavonoid production.

Flavonoids are compounds that protect plants from environmental stressors such as UV light and drought. The shift in metabolic activity enables the plant to conserve energy, improve photosynthesis efficiency, and protect itself from the harsh conditions brought on by drought. ″This adaptive shift is a very exciting finding, it shows how plants can reallocate their resources to survive under stress″, Ana I. Caño-Delgado says.

In their experiments, researchers generated mutant sorghum plants with a loss-of-function mutation in the SbBRI1 gene, to produce inactive BRI1 receptors. These mutant plants were tested under controlled drought conditions, and the results were remarkable. Compared to their non-mutated counterparts, the mutant plants displayed significantly improved water retention and photosynthetic efficiency, showing that BRI1 protein enchances the susceptibility to drought in sorghum.

When analysing these Sbbri1 mutant plants more in depth, researchers found that they were defective in a specific molecular route: the phenylpropanoid pathway, leading to reduced levels of lignin precursors and accumulation of flavone.

″One of the most striking findings was how well these plants maintained photosynthesis during severe drought″, says Juan Fontanet-Manzaneque, the first author of the study. ″Normally, drought causes a decrease in photosynthesis, which leads to stunted growth and lower yields. But these mutants kept functioning at a higher level, which could mean better yields under drought conditions″.

Potential impact on global agriculture

This discovery is more than just a scientific breakthrough; it holds tremendous potential for improving food security in regions vulnerable to climate change. As droughts become more frequent and severe, the ability to grow crops that are more resilient to these conditions will be crucial for maintaining stable food supplies.

Sorghum is already a staple crop in many dry regions, and by leveraging this knowledge, breeders could develop new varieties that are even more drought-tolerant. This research could also extend beyond sorghum. The BRI1 receptor exists in many plants, including maize, wheat, and rice, which are even more vulnerable to drought. ″Undertanding the brassinosteroid signaling in sorghum is key to develop climate-resilient agriculture″ Ana I. Caño-Delgado explains.

Reference article

Juan B. Fontanet-Manzaneque, Natalie Laibach, Iván Herrero-García, Veredas Coleto-Alcudia, David Blasco-Escámez, Chen Zhang, Luis Orduña, Saleh Alseekh, Sara Miller, Nanna Bjarnholt, Alisdair R. Fernie, José Tomás Matus, Ana I. Caño-Delgado. Untargeted mutagenesis of brassinosteroid receptor SbBRI1 confers drought tolerance by altering phenylpropanoid metabolism in Sorghum bicolor. Plant Biotechnology Journal, https://doi.org/10.1111/pbi.14461

About the authors and funding of the study

A.I.C.-D has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement 683163). J.B.F.-M., I.H.G and D.B.-E. were funded by ERC-2015-CoG-683163 granted to A.I.C.-D. J.B.F.-M. has received funding from the Ministry of Science, Innovation and Universities of Spain Grant PID2020-118218RB. N.L. has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No: 945043 and was additionally supported by grant CEX2019-000902-S funded by MCIN/AEI/10.13039/501100011033. I.H.G. is funded by FPU19/04332 grant from the Spanish Ministry of Universities. V.C.-A. is recipient of grant PRE2019-088780 funded by MCIN/AEI/10.13039/501100011033 and by ‘ESF Investing in your future’. L.O. was supported by FPI scholarship (PRE2019-088044), provided by MCIN/AEI/10.13039/501100011033 and FSE ‘invierte en tu futuro’. J.T.M. acknowledges the Grant PID2021- 128865NB-100, provided by MCI-N/AEI/10.13039/501100011033/ and FEDER ‘Una manera de hacer Europa’. C.Z. is supported by China Scholarship Council (CSC; no.: 201906300087). S.A. and A.R.F. acknowledge the European Union’s Horizon 2020 research and innovation programme, project PlantaSYST (SGA-CSA No: 739582 under FPA No: 664620) and the BG05M2OP001-1.003-001-C01 project, financed by the European Regional Development Fund through the Bulgarian ‘Science and Education for Smart Growth’ Operational Programme. S.M. and N.B. acknowledge the support from VILLUM FONDEN, Denmark, Grant No: 19151, awarded to N.B., and the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No: 801199, awarded to S.M.