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. However, despite intensive study of vascular development, the full diversity of cell types and the gene networks engaged are still poorly understood. 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. 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. Analysis of these marker genes’ expression dynamics enables reconstruction of the cell differentiation trajectories involved in phloem and xylem development. 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. 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.

中文翻译：

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单细胞分辨率下高度木质化杨树茎的转录景观


植物的次生生长取决于维管形成层的活性，维管形成层产生木质部和韧皮部。来自木质部的木材是全球最丰富的生物质形式，在整个人类历史中发挥着关键的社会经济和生存作用。然而，尽管对血管发育进行了深入研究，但细胞类型的全部多样性和所涉及的基因网络仍然知之甚少。在这里，我们应用了优化的原生质体分离方案和 RNA 测序来表征高度木质化杨树茎的高分辨率单细胞转录景观。我们鉴定了 20 个具有一系列新的簇特异性标记基因的假定细胞簇，并发现这些细胞基于转录组具有高度异质性。对这些标记基因表达动态的分析能够重建涉及韧皮部和木质部发育的细胞分化轨迹。我们发现不同的细胞簇表现出不同的植物激素反应模式，并强调使用我们的数据来预测潜在的基因冗余并识别与树木维管发育相关的候选基因。这些发现以单细胞分辨率建立了杨树茎主要细胞类型的转录图谱，并为研究树木维管细胞规范和分化的基本原理提供了宝贵的资源。