背景回顾：High-throughput single-cell RNA sequencing (scRNA-seq) has advantages over traditional RNA-seq to explore spatiotemporal information on gene dynamic expressions in heterogenous tissues. 

主要研究：We performed Drop-seq, a method for the dropwise sequestration of single cells for sequencing, on protoplasts from the differentiating xylem of Populus alba × Populus glandulosa. 

结果1-细胞数与细胞类群数：The scRNA-seq profiled 9,798 cells, which were grouped into 12 clusters. 

结果2-细胞类型鉴定：Through characterization of differentially expressed genes in each cluster and RNA in situ hybridizations, we identified vessel cells, fiber cells, ray parenchyma cells and xylem precursor cells. 

结果3-细胞轨迹分析：Diffusion pseudotime analyses revealed the differentiating trajectory of vessels, fiber cells and ray parenchyma cells and indicated a different differentiation process between vessels and fiber cells, and a similar differentiation process between fiber cells and ray parenchyma cells. 

结果4-标记基因鉴定：We identified marker genes for each cell type (cluster) and key candidate regulators during developmental stages of xylem cell differentiation. 

结论：Our study generates a high resolution expression atlas of wood formation at the single cell level and provides valuable information on wood formation.

 摘 要 

高通量单细胞RNA测序（scRNA-seq）相比于传统的RNA-seq具有明显的优势，能够同时从时空层面研究异质性组织的基因动态表达。作者采用了一种液滴测序Drop-seq的单细胞测序方法，对用银腺杨已分化的木质部制备的原生质体进行了scRNA-seq。最终，作者获得了9789个测序的细胞，可以聚成12个细胞类群。通过对每一个细胞类群中差异基因的鉴定和RNA原位杂交，作者鉴定到了导管细胞、纤维细胞、射线薄壁细胞和木质部前体细胞。扩散拟时分析揭示了导管细胞、纤维细胞和射线薄壁细胞的分化轨迹，揭示了导管和纤维细胞之间的不同的细胞分化进程，以及纤维细胞和射线薄壁细胞之间相似的细胞分化进程。作者还鉴定了木质部细胞分化过程中过不同发育阶段每一个细胞类型的标记基因和关键调控基因。本文的研究从单细胞层面上揭示了木材形成的高分辨率表达谱，为木材形成的研究提供了宝贵的信息。