Low temperature modulates spike development and yield via ABA pathway at post-reproductive transition stage in wheat.

Wheat (Triticum aestivum L.) yield is very sensitive to environmental temperature. Here, we integrated field sowing experiments and controlled-temperature treatments to explore how low temperature affects spike differentiation and yield formation in wheat. Early sowing allowed the wheat to undergo the reproductive transition before the winter, supporting prolonged spikelet differentiation under low-temperature conditions. By contrast, late sowing markedly shortened the reproductive growth period, reducing effective tiller number per plant and grain number per spike. Exposure to low temperature after the reproductive transition (Vs) significantly delayed heading while increasing spike length, the number of fertile spikelets, and the number of grains per spike. Temperature-gradient experiments (8, 16, and 22 °C) revealed that abscisic acid (ABA) signaling functions as a central hub integrating temperature cues: ABA signaling activates plant defense against cold at 8 °C, maintains developmental homeostasis at 16 °C, and is suppressed at 22 °C to prioritize reproductive growth. Integrated transcriptomic and plant hormonal analyses during floret differentiation showed that Vs treatment triggered extensive transcriptional reprogramming, with significant enrichment of phytohormone signaling pathways. These observations reveal that exposure to low temperatures after the reproductive transition, rather than vegetative vernalization, optimizes yield potential through ABA-mediated transcriptional reprogramming and crosstalk among multiple plant hormones. This provides a theoretical basis and molecular targets for optimizing sowing time and breeding climate-resilient wheat varieties under global climate change.