Single-nucleus and spatial transcriptomics reveal the cell populations of intercalary meristems in bamboo

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.