ABSTRACT
Vascular plants provide most of the biomass, food, and feed on earth, yet the molecular innovations that led to the evolution of their conductive tissues are unknown. Here, we reveal the evolutionary trajectory for the heterodimeric TMO5/LHW transcription factor complex, which is rate-limiting for vascular cell proliferation in Arabidopsis thaliana Both regulators have origins predating vascular tissue emergence, and even terrestrialization. We further show that TMO5 evolved its modern function, including dimerization with LHW, at the origin of land plants. A second innovation in LHW, coinciding with vascular plant emergence, conditioned obligate heterodimerization and generated the critical function in vascular development in Arabidopsis In summary, our results suggest that the division potential of vascular cells may have been an important factor contributing to the evolution of vascular plants.
Subject(s)
Arabidopsis Proteins/genetics , Arabidopsis/genetics , Basic Helix-Loop-Helix Transcription Factors/genetics , Evolution, Molecular , Gene Expression Regulation, Developmental , Gene Expression Regulation, Plant , Trans-Activators/genetics , Arabidopsis Proteins/metabolism , Basic Helix-Loop-Helix Transcription Factors/metabolism , Cell Proliferation/genetics , Phloem/cytology , Phloem/growth & development , Phloem/metabolism , Phylogeny , Plants, Genetically Modified , Protein Multimerization/genetics , Trans-Activators/metabolism , Xylem/cytology , Xylem/growth & development , Xylem/metabolismABSTRACT
During early plant embryogenesis, precursors for all major tissues and stem cells are formed. While several components of the regulatory framework are known, how cell fates are instructed by genome-wide transcriptional activity remains unanswered-in part because of difficulties in capturing transcriptome changes at cellular resolution. Here, we have adapted a two-component transgenic labelling system to purify cell-type-specific nuclear RNA and generate a transcriptome atlas of early Arabidopsis embryo development, with a focus on root stem cell niche formation. We validated the dataset through gene expression analysis, and show that gene activity shifts in a spatio-temporal manner, probably signifying transcriptional reprogramming, to induce developmental processes reflecting cell states and state transitions. This atlas provides the most comprehensive tissue- and cell-specific description of genome-wide gene activity in the early plant embryo, and serves as a valuable resource for understanding the genetic control of early plant development.
