Abstract: The plant life cycle and the promise of crop yield start with successful seed germination, which requires an optimal balance between the phytohormones abscisic acid (ABA) and gibberellin (GA). Here, we report that the APETALA 2-type transcription factor SALT AND ABA RESPONSE ERF 1 (OsSAE1) antagonistically modulates ABA and GA signaling to control seed germination in rice (Oryza sativa L.). We show that knocking out OsSAE1 delays seed germination, concomitant with the accumulation of SLENDER RICE1 (OsSLR1), a GA signaling repressor DELLA protein; importantly, GA application rescued the seed germination defect of ossae1 mutants. OsSAE1 directly activates transcription of the GA biosynthesis gene OsKS1 and represses that of the GA metabolism gene OsGA2ox3, resulting in higher GA levels. Moreover, OsSLR1 physically interacts with ABA-INSENSITIVE 5 (OsABI5), a key ABA signaling component, enhancing the transcriptional activation capacity of OsABI5 toward its target genes to regulate seed germination. The temporal expression pattern of OsSAE1 supports its role in orchestrating GA and ABA signaling to modulate seed germination and seed dormancy. Different OsSAE1 haplotypes differentially affected OsSAE1 transcript levels and seed germination rates, illustrating the potential of the elite OsSAE1 haplotype for genetic improvement of seed germination. Overall, our study reveals that OsSAE1 controls rice seed germination by regulating the balance between ABA and GA, providing a pivotal selection target for breeding rice cultivars suitable for direct seeding.

Key words: antagonism of ABA?GA signaling, AP2 transcriptionfactor OsSAE1, elite haplotype, rice direct seeding, seed germi-nation