Dissecting the temporal genetic networks programming soybean embryo development from embryonic morphogenesis to post-germination.

Key message: Desiccation-stage transcription factors perform similar functions, with early ones focused on desiccation tolerance and later ones on development. Gene networks governing late embryo development diverge between soybean and Arabidopsis. To understand gene activities programming seed embryo development, we profiled the soybean embryo transcriptome across embryonic morphogenesis through post-germination. Transcriptomic landscapes across embryo development feature highly prevalent transcripts, categorized into early and late groups, with shared and distinct functions. During the mid-storage reserve accumulation stage, the upregulated genes are enriched with regulatory tasks at both the transcriptional and chromatin levels, including DNA methylation and chromatin remodeling. The epigenetic-related functions also dominate in the upregulated genes during germination, involving core histone variants and histone chaperones. Gene network analysis reveals both stage-specific modules and modules active across multiple stages. The desiccation-associated gene module integrates diverse transcription factors (TFs) that are sequentially active during different desiccation stages, transitioning from abiotic stress functions early on to developmental functions later. Two TFs, active during the early and mid-desiccation stages were functionally assessed in Arabidopsis overexpression lines to uncover their potential roles in desiccation processes. Interestingly, nearly half of the Arabidopsis orthologs of soybean TFs active in the desiccation-associated module are inactive during Arabidopsis desiccation. Our results reveal that chromatin and transcriptional regulation coordinate during mid-storage reserve accumulation, while distinct epigenetic mechanisms drive germination. Additionally, gene modules either perform stage-specific functions or are required across multiple stages, and gene networks during late embryogenesis diverge between soybean and Arabidopsis. Our studies provide new information on the biological processes and gene networks underlying development from embryonic morphogenesis to post-germination.