Single-cell transcriptomics unveils xylem cell development and evolution

Abstract

As the most abundant tissue on Earth, xylem is responsible for lateral growth in plants. Typical xylem has a radial system composed of ray parenchyma cells and an axial system of fusiform cells. In most angiosperms, fusiform cells are a combination of vessel elements for water transportation and libriform fibers for mechanical support, while both functions are performed together by tracheids in other vascular plants. However, little is known about the developmental programs and evolutionary relationships of these xylem cell types. Through both single-cell and laser-capture microdissection transcriptomic profiling, here we demonstrate the developmental lineages of ray and fusiform cells in stem-differentiating xylem across four divergent woody angiosperms. Cross-species analyses of single-cell trajectories reveal highly conserved ray, yet variable fusiform, lineages across angiosperms. Core eudicots Populus trichocarpa and Eucalyptus grandis share nearly identical fusiform lineages. The tracheids in the basal eudicot Trochodendron aralioides, an evolutionarily reversed character, exhibit strong transcriptomic similarity to vessel elements but not libriform fibers, suggesting that water transportation, instead of mechanical support, is the major feature. We also found that the more basal angiosperm Liriodendron chinense has a fusiform lineage distinct from that in core eudicots. This evo-developmental framework provides a comprehensive understanding of the formation of xylem cell lineages across multiple plant species spanning over a hundred million years of evolutionary history.

Single-cell transcriptomics unveils xylem cell development and evolution

“…Sequence data from this article can be found in the NCBI GEO under accession number GSE180121 [ 120 ]. For E. grandis , T. aralioides , and P. trichocarpa , the plate barcode and Illumina i7 index were used to extract raw reads belonging to E. grandis , T. aralioides , and P. trichocarpa (Additional file 16 ).…”

“…pyramidalis wood tissues [ 124 ], and RNA-seq data for P. trichocarpa SDX [ 125 ]. All custom code is available on Zenodo [ 126 ] and under the MIT license in the GitHub repository [ 127 ].…”