Decoding Rice Heat Tolerance at Anthesis: From Physiological Disruption to Molecular Regulation and Strategies for Climate Resilient Breeding

Global climate change has driven a persistent rise in surface temperatures, posing an existential threat to agricultural productivity and food security. Rice ( Oryza sativa L.), the primary staple crop for more than half the global population, is acutely vulnerable to heat stress during reproductive development, particularly at flowering. Brief exposure to temperatures exceeding 35 °C during anthesis severely impairs spikelet fertility, and projected increases of 2–4 °C by mid-century make understanding the mechanistic basis of rice thermo-tolerance a matter of urgency. This review provides a comprehensive, critically integrated synthesis of rice flowering responses to high-temperature stress, covering the sequential processes of floret opening, anther dehiscence, pollen viability, pollen germination, and pollen tube growth at physiological, biochemical, and molecular levels. We systematically evaluate key regulatory networks-including reactive oxygen species (ROS) signaling, calcium (Ca²⁺) second-messenger cascades, phytohormone homeostasis, heat shock protein (HSP) chaperone networks, and the endoplasmic reticulum (ER) unfolded protein response (UPR) and critically synthesize how thermo-tolerance QTLs TT1 , TT2 , and TT3 interconnect these pathways. We further examine emerging roles for epigenetic regulation and non-coding RNAs in thermo-memory and heat acclimation. Finally, we integrate molecular insights with genetic improvement strategies-ranging from conventional breeding and marker-assisted selection to CRISPR/Cas9 genome editing-alongside evidence-based agronomic practices targeting the anthesis window. By bridging mechanistic understanding with translational applications, this review identifies key unresolved questions and outlines priority research directions for developing thermally resilient rice varieties capable of sustaining productivity under ongoing climate warming.