ABA Delays Seed Germination and Seedling Establishment via ABI5-FLZ13 Module-Mediated Gene Repression in Arabidopsis. Arabidopsis

The phytohormone abscisic acid (ABA) has long been known for its role in inhibiting plant growth, but the underlying molecular mechanism remains to be further characterized. Here, we report that ABA suppresses seed germination and subsequent seedling establishment at the start of a plant life cycle, through transcriptional repression of a subset of growth-related genes involved in chlorophyll biosynthesis, photosynthesis, cell wall organization, and hormone signaling pathways. Additionally, our data reveals that inhibition of chloroplast biogenesis is a preferred target of ABA signaling and a bZIP transcription factor ABSCISIC ACID INSENSITIVE5 (ABI5) plays an important role during this process. Furthermore, by employing proximity-labeling-based proteomic approach, we identify FCS-LIKE ZINC FINGER PROTEIN 13 (FLZ13) as an up-to-now unknown ABI5-interacting partner, which works synergistically with ABI5 to downregulate the transcription of ABA-repressed and growth-related genes, thereby coordinately modulating seed germination and seedling establishment in response to ABA. Collectively, our study reveals a previously uncharacterized transcriptional regulatory mechanism regarding ABA-mediated inhibition of plant growth.