The hub transcription factor ZmbZIP29 controls the speed of seed germination by promoting starch degradation within the maize embryo

Starch serves as a crucial energy source for seed germination. The classic starch degradation model focuses primarily on the endosperm during late germination, but little is known about starch mobilization within the embryo during early germination stages. Using transcriptomics and weighted gene co-expression network analysis, we identified ZmbZIP29 as a hub transcription factor that regulates early germination. ZmbZIP29 transcripts accumulate primarily in the aleurone layer, scutellum, radicle, and coleoptile during early germination. Our findings indicated that the maize embryo uses its local starch for a rapid energy supply within the first 12 hours after imbibition. Knockout of ZmbZIP29 reduced starch degradation rate, amylase activity, and downstream sugar content, ultimately delaying germination and reducing seedling robustness. ZmbZIP29 positively regulates the expression of three starch degradation genes by binding to classical ABRE elements within the ZmDPE2 and ZmGWD promoters, as well as a newly identified early germination element within an intron of ZmAMY1. These results reveal novel genes and regulatory mechanisms for mobilization of embryonic starch during early germination, significantly deepening our understanding of seed germination.