Integrated Molecular and Physiological Mechanisms Underlying Rice Adaptation to Heat, Salinity, and Drought Stress

Rice faces increasing threats from climate change, driven by heat, salinity, and drought stresses. Although researchers have extensively studied individual stresses, growing evidence indicates that combined stresses elicit unique physiological, biochemical, and molecular responses that single-stress studies cannot predict. This review comprehensively synthesizes current knowledge of the integrated signaling networks and adaptive mechanisms underlying rice responses to heat, salinity, and drought stress, with particular emphasis on stress crosstalk and multi-stress responses. We examine the roles of mechanosensitive ion channels, calcium signaling, salt overly sensitive (SOS) pathway, heat shock response regulators, mitogen-activated protein kinase (MAPK) cascades, and ABA-dependent and -independent signaling networks in stress tolerance systems. Furthermore, we discuss major adaptive responses involving reactive oxygen species (ROS) homeostasis, osmoprotectant accumulation, antioxidant defense systems, and phytohormone crosstalk involving abscisic acid, auxin, salicylic acid, cytokinin, brassinosteroids, ethylene, and gibberellins. Particular attention is given to the detrimental effects of combined stresses on growth, development, and yield. In addition, recent advances in enhancing stress tolerance through CRISPR/Cas9-mediated genome editing, marker-assisted breeding, and molecular marker technologies are also highlighted. Despite significant progress, critical knowledge gaps remain regarding primary stress-sensing mechanisms, epigenetic stress memory, organelle-specific signaling, and the translation of laboratory findings to field conditions. By integrating current knowledge across molecular, physiological, and breeding perspectives, we provide a comprehensive integrated signaling network model and crosstalk among signaling pathways for understanding rice adaptation to combined stresses and highlight potential strategies for enhancing crop resilience and global food security.