Distinct identities of leaf phloem cells revealed by single cell transcriptomics

第一作者：Ji-Yun Kim

第一单位：德国杜塞尔多夫大学

通讯作者：Wolf B Frommer

 Abstract 

背景回顾：The leaf vasculature plays a key role in solute translocation. Veins consist of at least seven distinct cell types, with specific roles in transport, metabolism, and signaling.

提出问题：Little is known about leaf vascular cells, in particular the phloem parenchyma (PP). 

研究对象：PP effluxes sucrose into the apoplasm as a basis for phloem loading, yet PP has been characterized only microscopically.

主要研究：Here, we enriched vascular cells from Arabidopsis leaves to generate a single-cell transcriptome atlas of leaf vasculature.

结果1-细胞聚类：We identified at least 19 cell clusters, encompassing epidermis, guard cells, hydathodes, mesophyll, and all vascular cell types, and used metabolic pathway analysis to define their roles.

结果2-功能富集：Clusters comprising PP cells were enriched for transporters, including SWEET11 and SWEET12 sucrose and UmamiT amino acid efflux carriers.

结果3-PP与韧皮部：We provide evidence that PP development occurs independently from APL, a transcription factor required for phloem differentiation. 

结果4-PP独特特征：PP cells have a unique pattern of amino acid metabolism activity distinct from companion cells (CC), explaining differential distribution/metabolism of amino acids in veins.

结果5-PP与CC：The kinship relation of the vascular clusters is strikingly similar to the vein morphology, except for a clear separation of CC from the other vascular cells including PP.

结论：In summary, our scRNA-seq analysis provides a wide range of information into the leaf vasculature and the role and relationship of the leaf cell types

 摘 要 

叶片维管组织在溶质迁移中发挥重要作用。叶脉至少由七种不同的细胞类型组成，每一种细胞类型都有其特异的作用，比如转运、代谢和信号转导。对于叶片中的维管细胞，尤其是韧皮部薄壁组织，我们目前的认识较为浅薄。韧皮部薄壁组织将蔗糖往外运输到质外体，由此构成了韧皮部装载的基础，但是目前我们也仅仅从显微结构大的角度认识了韧皮部薄壁组织。本文中，作者从拟南芥的叶片中富集维管细胞，并进行了单细胞转录组测序，获得了叶片维管的scRNA转录图谱。作者鉴定了至少19个细胞群，包括表皮、保卫细胞、吐水细胞、叶肉细胞以及各种其他维管细胞类型，并且通过代谢通路分析定义了这些细胞的作用。包含韧皮部薄壁细胞的细胞群富集到了转运蛋白，包括SWEET11和SWEET12蔗糖和鲜味氨基酸外排载体。作者发现韧皮部薄壁组织的发育独立于韧皮部分化必需转录因子APL。韧皮部薄壁细胞具有独特的氨基酸代谢模式，与伴胞明显不同，这也解释了叶脉中差异的氨基酸分布/代谢。维管细胞的聚类群与叶脉形态学的聚类十分相近，只是伴胞与包括韧皮部薄壁细胞在内的其它维管细胞有明显的分化。综上，本文所报道的拟南芥叶片维管组织单细胞转录组分析为叶片的维管以及叶片不同细胞类型之间的关系提供了广泛的信息。

 通讯作者 

**Wolf B. Frommer**

doi: https://doi.org/10.1093/plcell/koaa060

Journal: Plant Cell

Published date: Jan 07, 2021