Single-cell spatiotemporal transcriptomics reveals the developmental dynamics and regulatory network of poplar seed fibers

Poplar seed fibers cause environmental and health concerns, yet their developmental mechanisms remain poorly understood. Here, we constructed a high-resolution spatiotemporal transcriptomic atlas of female poplar capsules by integrating single-nucleus and spatial transcriptomics. We delineated the developmental trajectory of seed fibers, confirming their origin from placenta cells, and identified three functionally distinct fiber cell subtypes involved in initiation, metabolic support, and elongation. Weighted gene co-expression network analysis (WGCNA) identified several hub transcription factors, including PtoMYB , PtoHDT1 , PtoEIF6 and PtoPDF2 , that may serve as key regulators of fiber development. Our study provides a cellular-resolution framework for understanding trichome development in woody perennials and offers candidate targets for functional characterization toward breeding low-fluff poplar cultivars.