ZmSSRP1-mediated chromatin accessibility modulates maize development via regulation of ZmBRD1 transcription

The FAcilitates Chromatin Transcription (FACT) complex, comprising structure-specific recognition protein 1 (SSRP1) and suppressor of Ty 16 (SPT16), plays a key role in regulating gene transcription by facilitating ATP-independent nucleosome assembly. SSRP1 contains an HMG domain that binds to DNA and regulates cell proliferation, apoptosis, and DNA repair. However, its role in plant development remains poorly understood. In this study, we identified a mutant, small kernel 301 (smk301), characterized by reduced kernel size and semi-dwarfism. Map-based cloning revealed that the mutation affects ZmSSRP1 on chromosome 8, which is expressed throughout maize (Zea mays L.) tissues. ZmSSRP1 localizes to the nucleus and interacts with ZmSPT16 to form the FACT complex. Using RNA-seq and ATAC-seq analyses, we identified 3 candidate target genes involved in hormone pathways, all of which show a significant positive correlation with ZmSSRP1 expression. Notably, ZmSSRP1 was enriched in the chromatin open region of brassinosteroid-deficient dwarf 1 (ZmBRD1), which encodes a Brassinosteroid C-6 Oxidase. This indicates that ZmSSRP1 affects maize development by regulating the transcription of ZmBRD1, thereby influencing the brassinosteroid content in maize. Our findings shed light on how the FACT complex influences maize development by modulating the expression of brassinosteroid-related genes, offering insights into the molecular mechanisms underlying plant growth.