Improving Drought Resistance in Crops and Arabidopsis

Despite the massive amount of information gathered around the functions and mechanisms of Brassinosteroids (BRs) in plants, an important limitation persists in our knowledge of this signaling pathway: almost all we know comes from observations on the BRI1 receptor pathway, that is essential for growth and development, and for which mutants are highly pleiotropic and typically dwarf. Since the discovery of BRI1-like receptors (BRL1/3), we still do not really grasp what are their fundamental functions in plants. Twenty years of research have resumed the analysis of BRLs as redundant BRI1 receptors with a marginal vascular expression and lack of apparent mutant phenotypes. Currently, the work funded by ERC CoG “IDRICA” takes a novel perspective to explore the function of BRLs receptors in Arabidopsis plants, to understand the inner working of this pathway. We have shown that overexpression of BRL3-receptors confers drought resistance invited to investigate the components of BRL3 pathway in Arabidopsis. In the framework of ERC CoG IDRICA, novel components in this BRL3 steroid receptor pathway have been characterised that are essential to plant adaption to adverse climate. In particular we discover a native role for the vascular BRL3 receptor in plant adaptation to elevated temperatures in Arabidopsis and Sorghum, and identified the main components of this novel signaling pathway. Our new data changes the paradigm for our present understanding of BR signaling in plants and open new possibilities for producing better adapted crops. Thus, we generated new lines of Sorghum cereal that are more tolerant to drought. Our research, while contributing to the general understanding of plant steroid signaling and directly impacts on the sustainable production of climate resilient crops.

By accomplishing the proposed goals of the ERC CoG grant IDRICA we have identified and characterized a number of key molecular components of the Brassinosteroid (BR)-signaling pathway, which is essential for plant adaptation to drought and eleveted temperatures. In Objective 1. The local function of BRL3 receptors have been characterised in Arabidopsis, we has discovered that vascular brassinosteroid receptors BRL3 confer drought-resistant plants without penalising drought (Fabregas et al., Nat Comms 2018). In addition, we obtained unprecedented results on the identification of novel conditional phenotypes for brl3 mutants to different abiotic stresses, including elevated temperatures and increased CO2 levels. We found that brl3 mutants phenotypes can be recovered when the receptor are localised to the vascular phloem cells (Gupta., et al., Nat Plants; under revision). These experimental results not only change the paradigm for our present understanding of BR signaling in plants but also demonstrate the working hypothesis of the ERC CoG proposing that a vascular (stem) cell-specific signalling might be able to uncouple growth from adaptation to stress in the plant. In the years to come, engineering vascular cell-specific signaling pathways stands as a unique opportunity to improve plant adaptation to stress and impact in agriculture towards the solution of the food security crisis in the current climate change globally.

Also in the context of the ERC CoG, we have developed novel tools for plant data integration and analysis and developed software tools for this purpose (Betegon,et al., Plant Journal 2019). We have found a tight correlation between transcriptional responses of plants with increased BR receptor BRL3 levels and the accumulation of osmoprotectant metabolites (sugars and aminoacids) in the root by metabolomics analysis (Fabregas et al., Nat Comms 2018). To this aim, we are also developing a new software tool (TOTEM, a web tool that calculates tissue-enrichment values over an input gene list and visual representation. The latest developments in this direction include the singe-cell transcriptomics resolution that has also been achieved in the context of Obj. 2 of this ERC grant that will be publicly available here Lozano, Coleto et al., ms. under preparation. These new tools will be instrumental for the accomplishment of the genetic and chemicals screenings proposed in Objective 2.

In Objetive 3, we have transferred our fundamental findings in Arabidopsis to cereal Sorghum. We identified and characterised mutants for BRI1-like family member in Sorghum. We carried genetic analysis and established the set up microscopical and multi -omics tools for the analysis of root using embryonic roots. The initial characterisation of the BRI1 receptor mutants is under review (Rico-Medina et al., submitted). Finally, our greatest efforts in Sorghum are oriented towards the establishment of gene transformation protocols in order to lead genomic edition of most interested genes to improve drought resistance.
Overall, our proposal advance novel mechanisms for the molecular understanding of plants to drought stress adaptation mediated by brassinosteroid hormones, while transfers all the technologies and knowhow into agricultural value in order to improve cereal production in climate change scenarios using sorghum as a model.

Please find below the summary of the accomplished results for each proposed objective of IDRICA.
Objective 1- We managed to accomplish the tasks proposed in this objective faster than proposed. As a results number of novel results linked to the phenotypes of brl3 mutants in response to genomic and abiotic stresses that encourage the rapid progress of the project. For example, we have new results linking the role of BRL3 receptors in flowering and photoperiodism that were originally unplanned.
Objective 2- we did not go beyond the state of the art because we have not been able to establish the root phenotyping as we did not have a phenotyping facility at CRAG. Anyway, we have found an alternative way of establishing a custom phenotyping system that will enable the high throughput analyses of our plants and catch up in time the IDRICA proposed schedule. We use hytpocotyl phenotype of brl3 mutants that was found along the course of Obj. 1.
Objective 3- We accomplished the proposed tasks as proposed. In addition, we also performed the molecular analysis of BRL3 promoter in Sorghum. Although this was not proposed in the the project, we dedicated effort to establish Sorghum transformation methods, to further chase our scientific and agronomic objectives. Above all, we are doing our best to rapid transfer of the project from model system Arabidopsis to Sorghum. In addition, as part of Obj. 3, we have been able to carry an unprecedented visualization of sorghum stem cells in the root apex, establish a number of physiological, biochemical and molecular assays that will be extremely useful for the study of cereal Sorghum in the years to come.

Periodic Reporting for period 4 - IDRICA (Improving Drought Resistance in Crops and Arabidopsis)

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