Cell-specific transcriptomic analyses of three-dimensional shoot development in the moss Physcomitrella patens.

Area of Science:

• Plant biology
• Developmental biology
• Evolutionary biology

Background:

• Haploid moss gametophytes possess distinct stem cell populations: tip cells for filamentous growth and bud cells for axial shoot development.
• The transition from filamentous to triplanar growth in mosses is a key evolutionary step, potentially mirroring the development of early terrestrial plants from algal ancestors.
• Understanding the molecular mechanisms underlying this growth transition is crucial for comprehending the evolution of complex plant body plans.

Purpose of the Study:

• To investigate the molecular programs governing the transition from uniplanar to triplanar meristematic growth in mosses.
• To identify differentially expressed genes distinguishing protonematal tip cells from gametophore bud cells in *Physcomitrella patens*.

Main Methods:

• Utilized single-cell type transcriptomics to analyze gene expression profiles.
• Compared transcriptomes of uniplanar protonematal tip cells and multiplanar gametophore bud cells.

Main Results:

• Identified over 4000 differentially expressed genes between tip and bud cells.
• Both cell types exhibit molecular signatures of proliferative cells.
• Bud cells show a broader range of genes with significantly increased transcript abundance compared to tip cells.

Conclusions:

• The transition to triplanar growth involves a complex interplay of genes related to shoot patterning and asymmetric cell division.
• These findings provide molecular insights into the evolution of plant multicellularity and complex body plans.