Hypomagnetic field inhibits seed germination via ROS signaling and reprogramming transcriptome in Arabidopsis thaliana

The geomagnetic field (GMF) is a ubiquitous yet poorly understood environmental factor that affects plant growth and development. It has been suggested that the blue-light photoreceptor cryptochrome (CRY) functions as a critical magnetic-field sensor in birds and insects through the radical-pair mechanism (RPM). However, whether CRY acts as a bona fide transducer of GMF signals and what are the downstream cascades remain largely elusive in plants. To address these key issues, we generated hypomagnetic field (HMF) via Helmholtz coils and passive magnetic shielding to investigate the GMF deprivation effects in Arabidopsis thaliana. HMF significantly delays the germination speed without altering the final germination rate, suggesting that HMF specifically modulates germination kinetics rather than seed viability. Time-resolved transcriptomic profiling revealed a coordinated transcriptional shift characterized by downregulation of growth-promoting genes and concurrent upregulation of defense-related genes under HMF. This biphasic transcriptional reprogramming coincides with a significant increase of reactive oxygen species (ROS), linking redox perturbation to the germination delay. Consistently, supplementation with ROS-scavenging antioxidants (e.g., reduced glutathione and ascorbic acid) rescues both germination speed and the misregulated expression of a subset of HMF-responsive genes, suggesting the central role of ROS in mediating HMF bioeffects. Genetic analysis using cry1 cry2 double mutants further indicated that HMF-induced germination delay operates through both CRY-dependent and -independent signaling pathways, suggesting the involvement of additional magnetosensitive modules beyond the canonical CRY-based RPM. These findings suggest that the GMF acts as a positive environmental cue that fine tunes the growth-defense trade-off through a redox-dependent signaling.