Key signaling pathways regulating gene expression during seed germination

Seed germination represents a pivotal developmental transition in the plant life cycle, orchestrated by intricate signaling networks that integrate environmental cues with internal hormonal dynamics. This review presents a comprehensive synthesis of major signaling pathways—including light, temperature, and reactive oxygen species (ROS)—that modulate germination through transcriptional and post-translational mechanisms. Photoreceptors such as phytochromes (phys) and cryptochromes (crys) regulate the antagonistic interaction between gibberellic acid (GA) and abscisic acid (ABA), promoting germination across species. Thermal extremes induce thermoinhibition via enhanced ABA biosynthesis and suppressed GA signaling, mediated by phyB, PHYTOCHROME INTERACTING FACTORS (PIF), and DELAY OF GERMINATION1 (DOG1). Nitrate and its downstream effector, nitric oxide, alleviate dormancy by promoting ABA catabolism and activating key regulators such as NIN-like protein 8 (NLP8). ROS operate as dual regulators: at moderate levels, they promote germination by stimulating mitogen-activated protein kinase-mediated GA biosynthesis and ABA degradation; in excess, they induce seed aging and loss of viability. Hormonal cross-talk, particularly between ABA and GA, integrates these pathways through central mediators such as ABA-INSENSITIVE 5 (ABI5), PIFs, and epigenetic regulators like POWERDRESS (PWR). A deeper understanding of these signaling mechanisms offers promising avenues for improving seed vigor and enhancing crop resilience under abiotic stress.