Heat priming improves spikelet fertility and seed germination under heat stress with proteomic changes in IR64 (Oryza sativa L.).

Heat stress during the reproductive stage severely impairs spikelet fertility and can negatively affect subsequent seed germination in rice. Heat priming has been proposed as an effective strategy to mitigate heat stress; however, its effects depending on the timing of application and the associated protein-level responses remain insufficiently understood. In this study, heat priming was applied to the heat-sensitive rice cultivar IR64 at the tillering and booting stages, followed by heat stress at the flowering stage, to evaluate its effects on growth, reproductive traits, and progeny seed germination, together with associated proteomic changes. Heat stress significantly reduced spikelet fertility and delayed progeny germination. In contrast, heat-primed plants showed higher spikelet fertility and faster germination than non-primed plants under heat stress conditions. Under the present experimental conditions, tillering-stage priming showed greater improvements in these traits than booting-stage priming. Proteomic analysis revealed distinct protein abundance patterns between heat-primed and non-primed plants under heat stress, with a higher number of differentially abundant proteins observed following tillering-stage priming. The identified proteins were mainly associated with stress response and redox homeostasis, carbon metabolism and energy allocation, and protein synthesis and cellular regulation. The differences between the two priming treatments may reflect the combined effects of developmental stage and the priming-to-stress interval. Overall, these findings indicate that heat priming modified reproductive and progeny germination responses to subsequent heat stress in IR64 and was associated with changes across multiple protein functional categories.