The 11th International Symposium on Root Development

MicroRNAs (miRNAs) are key regulators of gene expression and are particularly important for root development, where they fine-tune cell proliferation, differentiation, and tissue patterning. To investigate how miRNA contributes to these processes in the root, we focused on SERRATE, a scaffold protein required for multiple steps of RNA metabolism, including miRNA processing. Using the hypomorphic mutant se-3, we observed a strong root phenotype characterized by premature meristem exhaustion and complete differentiation within seven days after germination, suggesting enhanced differentiation activity. Tissue-specific functional analyses indicate that SERRATE acts within the meristem, particularly from the ground tissue, where it influences transition zone positioning. RNA sequencing of se-3 root apices revealed defects in miRNA maturation and the accumulation of target transcripts, pointing to downstream regulatory pathways. In particular, our data suggest that altered miRNA activity impacts cell expansion programs through EXPANSIN genes, and we identify candidate miRNA targets that may control transition zone positioning.