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Improving Drought Resistance in Crops and Arabidopsis

Periodic Reporting for period 3 - IDRICA (Improving Drought Resistance in Crops and Arabidopsis)

Período documentado: 2019-11-01 hasta 2021-04-30

Drought is the primary cause of agricultural loss globally, and represents a major threat to food security. Currently, plant biotechnology stands as one of the most promising strategies to produce crops capable of producing high yields in rainfed conditions. From the study of whole plants, the main response mechanisms to drought stress have been uncovered, and multiple drought resistance genes have been engineered into crops. So far, most of the plants with enhanced drought resistance have displayed reduced crop yield, meaning there is a need to search for novel approaches to uncouple drought resistance from plant growth. In the framework of ERC CoG “IDRICA” we have recently shown that the receptors of brassinosteroid (BR) hormones use cell-specific pathways to allocate different developmental responses during root growth. In Arabidopsis, we have found that increasing BR receptor in the vascular plant tissues confers resistance to drought without penalizing yield, opening up an exceptional opportunity to investigate the mechanisms that confer drought resistance with cellular specificity in plants. Currently, our goal is to identify the most promising phenotypical drought traits that could be improved biotechnologically to obtain drought-tolerant crops, using Sorghum as a model cereal. Furthermore, we are implementing genome editing technologies in Sorghum in order to identify and manipulate novel genes able to confer resistance to drought stress. At the completion of IDRICA great contributions are expected in terms of the identification of sustainable solutions for enhancing crop production in water-limited environments.
During the first 30 months of the ERC CoG grant IDRICA we have started to characterize the molecular components of the Brassinosteroid (BR)-signaling involved in drought stress adaptation in Arabidopsis and have implemented great part of the proposed Objective 1. We have investigated the local roles of BR receptors in Arabidopsis, discovered that vascular brassinosteroid receptors BRL3 were also able to generate drought-resistant plants without penalizing drought (Fabregas et al., Nat Comms 2018). These findings support 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. Thus, engineering cell-specific signaling pathways in the plant offers 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 on Earth.
Furthermore, we have advanced in the capabilities 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) that will be released during the next months. These new tools will be instrumental for the accomplishment of the genetic and chemicals screenings proposed in Objective 2. Finally, we have started the transferred of our findings to cereal Sorghum. Right now, we have been able to set up microscopical tools for the analysis of root using embryonic roots. In addition, we have already identified BR-receptor mutations in Sorghum by TILLING that are under characterization. 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 is deeding in 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.

Figure 1. The BRL3 receptor pathway is a central regulator of drought stress responses. BRL3 receptors activates transcriptional responses in the phloem tissues that lead to the accumulation a sugar-enriched metabolic signature. Many of the accumulated sugars travel from shoot to roots where they act as osmoprotectants, which yield drought tolerant plants of normal size (Fabregas, Lozano, et al., 2018)
The project Objective 1 has evolved faster than expected, as we have identified a number of 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.
In Objective 2, we are not going 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.
At Objective 3, we are following the proposed task up and in light of our recent analysis we also encourage the molecular analysis of BRL3 promoter in Sorghum that will further input in the present state of the art in Objective 3. Above all, we are doing our best to rapid transfer of the project from model system Arabidopsis to Sorghum. We are so far limited by the technical difficulty on Sorghum transformation, but we are positive that will be able to do it soon. So far, no lab in Europe is able to stably transform this cereal, so it is essential to position our research lab in the field to achieve this goal, and we are investing our time and energy in this task. In addition, as part of Obj. 3, we have been able to carry an unprecedented visualization of sorghum stem cells in the root apex, we are also exploring how to perform single cell genomics of these cell vascular exposed to stress (not originally planned) and move faster in understanding how these cells contribute to drought stress adaptation in cereals.
Figure 1. The BRL3 receptor pathway is a central regulator of drought stress responses.