Heat stress impact on rice reproductive processes: challenges and new approaches.

Heat stress represents one of the most severe abiotic constraints to rice (Oryza sativa L.) productivity and is expected to intensify under ongoing climate change, particularly affecting the reproductive phase and leading to substantial yield and grain quality losses. This review synthesizes current knowledge on the impacts of heat stress on rice reproduction, with a focus on both male and female reproductive structures and their interactions. Evidence from anatomical, physiological, transcriptomic, and metabolomic studies to describe how elevated temperatures disrupt key reproductive processes, including microsporogenesis, anther dehiscence, pollen viability, pollen-pistil interactions, fertilisation, and embryo sac development were integrated in this review. It further discusses the genotype-dependent differences in reproductive thermotolerance; and key genes, metabolites, and pathways associated with heat stress perception, signalling, and tolerance are highlighted. Finally, it is briefly discussed how recent advances in breeding strategies, functional genomics and genome-editing technologies, particularly CRISPR-based approaches, are providing new opportunities to enhance reproductive resilience to heat stress and how it is essential to close the existing molecular knowledge gaps in the development of heat-tolerant rice varieties capable of sustaining productivity in a warming climate.