Temporal and spatial expression analysis of AtbZIP9 during seed and silique development in Arabidopsis thaliana (L.) Heynh

In Arabidopsis thaliana , seed dispersal is mediated by the silique, a specialized fruit that undergoes a complex developmental program involving cell division, expansion, and programmed cell death. Transcription factors (TFs) from the bZIP family are key regulators of these transitions. In this study, we focused on the C-group bZIP TF AtbZIP9 to characterize its expression, potential regulatory roles, and functional relevance during silique development and early seedling growth. Promoter-reporter assays and qPCR analyses revealed that AtbZIP9 is broadly expressed, with strong activity in vascular tissues and the funiculus during early and mid-stages of silique development. AtbZIP9 physically interacts with the S1-group member AtbZIP44, as shown by yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assays, supporting the formation of heterodimeric complexes. Despite the lack of major phenotypic alterations in AtbZIP9 knockout mutants during germination and early development—even under salt stress conditions—its co-expression with AtbZIP44 and the CW-modifying gene AtMAN7 suggests a role in transcriptional regulation during silique development. Recent evidence further links AtbZIP9 to ABA-responsive gene expression and identifies it as a likely component of redundant regulatory networks involving other C-group bZIPs. These findings highlight AtbZIP9 as a candidate transcriptional modulator of silique and seed developmental processes, potentially acting in coordination with AtbZIP44 and other factors.