Drought stands as the most devastating natural disaster in agricultural production. Annually, the crop yield reduction caused by drought surpasses the combined impact of all pests and diseases. With the intensification of climate change, the world is facing a hotter and drier future. It is projected that by 2050, five billion people will inhabit water – scarce regions. Although the global cultivated land area has increased, an additional one million hectares of arable land are required annually to ensure food security. Moreover, by 2050, the demand for freshwater in agriculture may double, while the availability of freshwater is expected to decrease by 50% due to climate change. Therefore, the protection of crops against drought has become extremely important.
Plant Traits Related to Drought Resistance
Plants respond to changes in soil moisture gradients by regulating physiological activities, such as modifying root growth and architecture and closing stomata in the above – ground parts. These tissue – specific responses alter the dynamics of cell signaling pathways, leading to early flowering, growth retardation, or yield decline. Physiological and molecular studies on the model plant Arabidopsis thaliana have shown that plant hormone signaling pathways are crucial for regulating responses to drought or water shortage.
Roots respond to changes in soil moisture at the cellular and whole – root structure scales. The root stem cell niche, meristem, and vascular system coordinate with each other to cope with drought stress. When water is scarce, the root architecture undergoes morphological changes to enhance its water – absorption capacity. These changes can be traced back to the coordination of cell division, elongation, and differentiation at the root tip. When it comes to water acquisition, the root architecture is related to depth. Deeper roots with smaller branching angles are more effective in obtaining water from deep soil (in severely arid areas). In contrast, a shallower root structure is beneficial for water uptake in soils with low rainfall. When the water distribution in the soil is uneven, auxin signaling mediates the growth of lateral roots and root tips towards areas with higher water content. The optimization of root architecture is an environmentally adaptive behavior.
Plants Utilize Hormones to Improve Drought Resistance
Drought stress triggers the production and accumulation of ABA in different plant organs and activates downstream signal transduction. The ABA pathway is an important strategy for regulating plant drought responses and optimizing water use efficiency. Research has shown that genetic engineering of the ABA receptor PYR1 can improve the drought resistance of Arabidopsis thaliana and tomatoes. The screening of ABA receptor agonists has identified a bioactive ABA analog, OP (opabactin), which can also activate the ABA signaling pathway, thereby enhancing plant drought resistance.
Improving Drought Resistance through Tissue - Specific Drought Responses
Although ABA in leaves can regulate stomatal opening and closing according to water availability, thereby maintaining water in plants, this comes at the cost of photosynthesis, growth, and yield. Therefore, most strategies for improving plant drought resistance focus on fine – tuning stomatal conductance and regulating ABA signaling through stomatal – specific promoters. Through optogenetics, scientists introduced BLINK1 (a light – activated synthetic K+ channel) into guard cells, synchronizing stomatal behavior more closely with changes in light conditions and achieving simultaneous improvement in stomatal performance and plant production. This indicates that engineering stomata can minimize carbon fixation losses and improve water use efficiency.
Plants optimize water uptake by adjusting root architecture (such as deep or shallow root systems) and hydrotropism. For example, the DEEPER ROOTING1 gene in rice promotes the formation of deep roots to enhance drought resistance. Stomata close rapidly through ABA signaling to reduce transpiration, but excessive closure inhibits photosynthesis. Optogenetic tools (such as BLINK1) can precisely regulate stomatal dynamics, balancing water loss and carbon fixation. ABA (abscisic acid) is a core regulator of hormonal synergy. It activates drought – resistant genes through the PYR/PYL receptor – SnRK2 kinase signaling cascade, driving stomatal closure and the synthesis of osmoregulatory substances (such as proline). Brassinosteroids (BRs) interact with ABA in a cross – regulatory manner. The BRL3 receptor enhances drought resistance by promoting the accumulation of osmoregulatory substances in roots and coordinating growth and stress responses. Other hormones, such as ethylene and auxin (e.g., EXO70A3 regulates root architecture), are involved in local or systemic signal transduction. The CLE25 peptide secreted by plant roots transmits drought signals to leaves through the vascular system, inducing ABA synthesis and stomatal closure to achieve whole – plant water balance.