Single-Cell and Spatial Multi-Omics Reveal Mechanical Stress Driving Heterogeneous Xylem Development in Populus [Phosphoproteomics]

Xylem, the predominant tissue for structural support, forms tension wood with G-layer-rich fibers under mechanical stress. Despite being recognized over a century ago, three key biological questions remained unclear: (1) Are fibers in normal and tension wood distinct cells due to morphological differences? (2) Do tension wood fibers arise from different lineages? (3) What are the key genes regulating tension wood formation? We conducted single-cell RNA-seq on normal, tension and opposite xylem. Fibers in normal and tension wood belong to the same cell type and lineage. Differential developmental speed and cell-type ratio in tension and opposite xylem were further validated by spatial transcriptomics and metabolomics. Phosphoproteomics uncovered mechanical sensing mechanisms conserved between stems and roots across angiosperms. We identified a group of genes involved in the cell fate transition in tension wood. The knowledge on the heterogeneity of cell development offers insights for optimizing biomass production and bioenergy yield.

木质部（Xylem）作为植物主要的结构支持组织，在机械胁迫条件下可形成富含G层纤维的张力木材。尽管该现象在一个多世纪前便已被学界认知，但仍有三个核心生物学问题尚未明确：(1) 正常木材与张力木材中的纤维是否因形态差异而属于不同的细胞类群？(2) 张力木材纤维是否起源于不同的细胞谱系？(3) 调控张力木材形成的关键基因是什么？本研究对正常木质部、张力木质部与对侧木质部开展了单细胞RNA测序（single-cell RNA-seq）。分析结果显示，正常木材与张力木材中的纤维属于同一细胞类型及细胞谱系。进一步通过空间转录组学（spatial transcriptomics）与代谢组学（metabolomics）验证了张力木质部与对侧木质部在发育速度及细胞类型比例上的差异。磷酸化蛋白质组学（phosphoproteomics）揭示了被子植物（angiosperms）茎与根之间保守的机械感应机制。本研究鉴定出一组参与张力木材细胞命运转变的基因。有关细胞发育异质性的研究成果，可为优化生物质生产与生物能源产量提供理论借鉴。