Abstract
Intercalary meristems (IcMs), specialized developmental zones that drive rapid stem elongation in monocots, exhibit distinct spatiotemporal dynamics; however, their genetic basis remains poorly understood due to their transient activity and cellular heterogeneity. Moso bamboo (Phyllostachys edulis)-with its exceptional daily growth rates of up to 114.5 cm, prolonged IcM activity spanning 45 to 60 d, and large, accessible culm structure-provides an ideal system for building a comprehensive IcM cell atlas. Here, we integrated a chromosome-level genome assembly of Moso bamboo with a high-resolution anatomical atlas to delineate three critical developmental stages of IcM activity: the initial cell division phase (ID), the rapid cell division phase (RD), and the rapid cell elongation phase (RE). By combining single-nucleus RNA sequencing (snRNA-seq) and spatial transcriptomics, we reconstructed a dynamic single-nucleus transcriptomic continuum spanning from proliferative to elongation states. Multiomics integration, along with in situ hybridization and ultrastructural imaging, identified IcM cells as short-columnar cells adjacent to elongating ground tissue parenchyma (Gp) cells, with the IcM1 subpopulation functioning as stem-like cells essential for maintaining the proliferative capacity. Pseudotemporal trajectory analysis revealed transcriptional transitions from stem-like IcM states to differentiated Gp cells. Functional experiments revealed that clrGene008562, a WOX2 homolog, enhances callus regeneration, indicating its potential role in promoting cell division and differentiation processes relevant to IcM development. These findings provide a comprehensive molecular and cellular framework for understanding IcM function and offer valuable multiomics resources for advancing meristem research in bamboo and other Poaceae species.