Take a Deep BReath: Manipulating brassinosteroid homeostasis helps cereals adapt to environmental stress

Global climate change leads to the increased occurrence of environmental stress (including drought and heat stress) during the vegetative and reproductive stages of cereal crop development. Thus, more attention should be given to developing new cereal cultivars with improved tolerance to environmental stress. However, during the development of new stress-tolerant cereal cultivars, the balance between improved stress responses (which occur at the expense of growth) and plant yield needs to be maintained. Thus, the urgent need for developing new cereal germplasm with improved stress tolerance could be fulfilled using semi-dwarf cereal mutants defective in brassinosteroid (BR) biosynthesis or signaling. BRs are steroid phytohormones that regulate various developmental and physiological processes throughout the plant life cycle. Mutants defective in BR biosynthesis or responses show reduced plant height (dwarfism or semi-dwarfism). Importantly, numerous reports indicate that genetic modification or biotechnological manipulation of BR biosynthesis or signaling genes in cereals such as rice (Oryza sativa), maize (Zea mays), wheat (Triticum aestivum), and barley (Hordeum vulgare), which are of crucial importance for global agriculture, may facilitate the development of cereal germplasm with improved stress tolerance. This review presents a comprehensive overview of the genetic manipulation of BR homeostasis in the above-mentioned cereal crops aimed at improving plant responses to various environmental stresses, such as drought, salinity, oxidative stress, thermal stress, and biotic stresses. We highlight target BR-related genes and the effects of genetic manipulation (gene editing, overexpression, silencing or miRNA-mediated regulation) on plant adaptability to various stresses and provide future perspectives.