Brassinosteroid-mediated drought tolerance in Arabidopsis thaliana and translation to Sorghum bicolor

Abstract

The present PhD thesis dissertation unveils novel mechanisms of the brassinosteroid receptor BRI1-LIKE 3 (BRL3) and its downstream molecular players in coping with abiotic stresses in Arabidopsis thaliana. Additionally, it reports a significant advancement in Sorghum bicolor genetic transformation, leading to the development of cultivars better adapted to drought stress. _x000D_ Brassinosteroids, essential plant steroid hormones, are perceived by plasma membrane leucine-rich repeat receptor-like kinases, with BRASSINOSTEROID INSENSITIVE 1 (BRI1) driving cell elongation and growth from the outer cell layers and BRL3 regulating drought and temperature stress adaptation from the vascular tissues. Through an interdisciplinary approach encompassing molecular biology, genetics, biotechnology, biochemistry, physiology, and bioinformatics, this thesis deciphers BRL3 transcriptional regulation under abiotic stress and its downstream transcription factors that modulate drought stress tolerance in Arabidopsis thaliana. _x000D_ Key findings include the characterization of CLASS III HOMEODOMAIN-LEUCINE ZIPPER (HD-Zip III) transcription factors in regulating BRL3 vascular expression and the uncovering novel roles for MYB transcription factors MYB96 (AT5G62470), MYB305 (AT3G24310), and HD-Zip II transcription factor HAT9 (AT2G22800) as critical players in vascular BRL3-mediated signaling through BRASSINAZOLE RESISTANT 1 (BZR1) to control plant abiotic stress adaptation._x000D_ In this PhD thesis, translational work of these findings to Sorghum bicolor, a cereal of great agronomical importance, demonstrates that modulation of brassinosteroid signaling can enhance abiotic stress tolerance in crops. By employing transcriptomics, metabolomics, and physiological assays of untargeted mutagenesis of the Sorghum BRI1 receptor, the study reveals BRI1 as a negative regulator of drought stress, primarily affecting the phenylpropanoid pathway involved in lignin and flavonoid synthesis. Additionally, the thesis establishes a highly efficient Agrobacterium-mediated transformation protocol for Sorghum bicolor, leveraging morphogenic regulators and a ternary vector system and overcoming the difficulty of genetic transformation in Sorghum for the first time in European academic laboratories. This breakthrough enabled the generation of transgenic plants that enhance Sorghum bicolor BRL3 receptor levels, resulting in plants better adapted to drought stress by altering leaf epinasty._x000D_ Overall, this dissertation not only deciphers novel components of the BRL3-mediated signaling in drought stress tolerance, but also paves the way for creating smart crops better adapted to climate change, underscoring the potential of brassinosteroid signaling modulation and advanced genetic transformation techniques in crop improvement.

Date of Award	12 Sept 2024
Original language	English
Supervisor	Ana Isabel Caño Delgado (Director)