Biological clock acts as an endogenous molecular timer in plants, coordinating and maintaining core physiological processes. Although multiple biological clock proteins have been proven to participate in controlling seed germination, whether this process is specifically regulated by time signals and its potential molecular mechanisms need further research.

In a study published in The Plant Cell, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences uncovered a key mechanism by which plants use their internal circadian clock to precisely time seed germination in response to environmental stresses, and demonstrated how core clock components directly regulated hormone signaling to optimize seedling emergence.

Researchers found that the seeds of wild-type Arabidopsis thaliana exhibited robust daily rhythms in germination rates under stress conditions (abscisic acid, salt, or osmotic stress). Seeds transferred to growth conditions at dawn showed the highest rates of germination and cotyledon greening, while those transferred near dusk had a significant decrease in germination success. However, the "high during the day and low at night" rhythm vanished in mutants of core clock genes, proving the clock’s essential role.

Furthermore, researchers revealed that the genes of the biological clock evening complex (ELF3, ELF4, and LUX) exhibited circadian rhythm expression during the seed germination stage, and their transcription levels were inhibited by abscisic acid (ABA). ELF3/ELF4/LUX physically interacted with ABA-activated transcription factors, ABI3 and ABI5, inhibiting their activity and promoting their degradation.

Notably, during the seed germination phase, transcriptional regulatory relationships still existed between the core components of the circadian clock genes, suggesting that these components might collaboratively regulate the seed germination process mediated by circadian rhythm signals.

"Our study reveals that evening complex proteins play a critical role in the regulation of gibberellin signaling and seed germination time by antagonizing ABI3 and ABI5. This mechanism is an important component in the plant seed germination regulatory network, which is of great significance for plants to adapt to environmental changes," said HU Yanru from XTBG.

This study elucidates how plants synchronize developmental processes with environmental cycles. By modulating ABA signaling intensity across the day-night cycle, the clock ensures that germination occurs at biologically favorable times, enhancing seedling survival.