Unraveling developmental patterns and differentiation trajectories in a single developing internode of Moso Bamboo (Phyllostachys edulis)

Bamboo, a significant carbon sink and eco-friendly resource, possesses substantial economic value and ecological benefits. A single internode represents the fundamental unit of bamboo culm, yet research focusing on the pivotal cellular destinies and molecular mechanisms underpinning the growth and development of a single internode remains comparatively scarce. In the study, we pioneered the establishment of a high-resolution single-cell transcriptomic atlas for a single internode of Moso bamboo. Utilizing known marker genes, we identified six major cell clusters (meristem, epidermis, phloem, xylem, pre-xylem/phloem, and vascular bundle sheath) and found many potential marker genes in the internode of Moso bamboo. Subsequently, we reconstructed the developmental trajectories of the epidermis and vascular tissues and further unveiled the key regulatory factors determining cell fates. Moreover, ectopic expression of PheIAA15 in Arabidopsis thaliana resulted in a marked reduction in the number of vascular bundles within the stems, as well as a significant decrease in their cross-sectional areas, diverging from existing research in Arabidopsis. The interaction between PheIAA15 and PheWOX4c suggested a potential novel auxin response mechanism in Moso bamboo. We subsequently elucidated that PheIAA15 bound to the promoter region of PheCLE25, thereby down-regulating the expression of PheCLE25, whereas PheWOX4c can activate the transcription of PheCLE25, which suggested that these two factors regulated the expression of PheCLE25 through an antagonistic mechanism. This finding highlighted the critical role of the complex regulatory network established among these elements in the differentiation of vascular tissues in the internodes of Moso bamboo. Overall, the study fills a critical research void concerning internodal development in bamboo plants at the single-cell level, laying a foundation for future studies to unravel the origin and differentiation of vascular bundle cells during internode development in perennial Gramineous plants.