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

Starch serves a crucial energy source for seed germination. While the classic starch-degradation model primarily focuses on the endosperm during late germination, little is known about starch mobilization within the embryo during the early stages. Through transcriptome analysis and weighted gene coexpression network analysis (WGCNA), we identified the transcription factor ZmbZIP29 as a hub gene regulating early germination. ZmbZIP29 transcripts primarily accumulate in the aleurone layer, scutellum, radicle, and coleoptile during early germination. Our findings indicate that the maize embryo utilizes its local starch for a rapid energy supply within the first 12 hours after imbibition. Knockout of ZmbZIP29 reduced the starch degradation rate, amylase activity, and downstream sugar content, subsequently leading to delayed germination and weakened seedling robustness. Furthermore, ZmbZIP29 positively regulates the expressions 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 (EGE) element within the ZmAMY1 gene intron. These results reveal novel genes and regulatory mechanisms for embryonic starch mobilization during early germination, significantly deepening our understanding of seed germination.