背景回顾：Plant secondary growth depends on the activity of the vascular cambium, which produces xylem and phloem. Wood derived from xylem is the most abundant form of biomass globally and has played key socio-economic and subsistence roles throughout human history. 

提出问题：However, despite intensive study of vascular development, the full diversity of cell types and the gene networks engaged are still poorly understood. 

主要研究：Here, we have applied an optimized protoplast isolation protocol and RNA sequencing to characterize the high-resolution single-cell transcriptional landscape of highly lignified poplar stems.

结果1-细胞类群和标记基因鉴定：We identify 20 putative cell clusters with a series of novel cluster-specific marker genes and find that these cells are highly heterogeneous based on the transcriptome. 

结果2-韧皮部和木质部发育轨迹：Analysis of these marker genes’ expression dynamics enables reconstruction of the cell differentiation trajectories involved in phloem and xylem development. 

结果3-激素响应模式、基因功能冗余：We find that different cell clusters exhibit distinct patterns of phytohormone responses and emphasize the use of our data to predict potential gene redundancy and identify candidate genes related to vascular development in trees. 

结论：These findings establish the transcriptional landscape of major cell types of poplar stems at single-cell resolution and provide a valuable resource for investigating basic principles of vascular cell specification and differentiation in trees.

 摘 要 

植物次生生长依赖于维管形成层的活性，而维管形成层是形成木质部和韧皮部的源头。木材来源于植物的木质部，是全球生物量最丰富的形式，在人类历史上一直发挥着十分重要的社会经济和生存作用。尽管对于植物维管的发育有了十分深入的研究，但是有关植物维管组织全部的细胞类型多态性及所涉及的基因调控网络仍然还不是很清楚。本文中，作者采用了优化的原生质体分离策略和RNA测序方法，检测杨树高度木质化茎段的高分辨率单细胞转录图谱。作者共鉴定了约20个细胞类群以及一系列的新的细胞类群特异性标记基因，发现这些细胞在转录层面上高度异质。通过对这些标记基因的表达动态分析，作者重建了韧皮部和木质部发育的细胞分化轨迹。作者发现不同的细胞类群存在不同的激素响应模式，并且利用了scRNA-seq数据预测了潜在的基因冗余性，鉴定了林木中与维管发育相关的候选基因。这些发现建立了杨树茎干中主要细胞类群的单细胞转录图谱，为林木维管细胞特化和分化的基础生物学研究提供了宝贵的资源。