Abstract
Trithorax group (TrxG) proteins are evolutionarily conserved in eukaryotes and play critical roles in transcriptional activation via deposition of histone H3 lysine 4 trimethylation (H3K4me3) in chromatin. Several Arabidopsis TrxG members have been characterized, and among them SET DOMAIN GROUP 2 (SDG2) has been shown to be necessary for global genome-wide H3K4me3 deposition. Although pleiotropic phenotypes have been uncovered in the sdg2 mutants, SDG2 function in the regulation of stem cell activity has remained largely unclear. Here, we investigate the sdg2 mutant root phenotype and demonstrate that SDG2 is required for primary root stem cell niche (SCN) maintenance as well as for lateral root SCN establishment. Loss of SDG2 results in drastically reduced H3K4me3 levels in root SCN and differentiated cells and causes the loss of auxin gradient maximum in the root quiescent centre. Elevated DNA damage is detected in the sdg2 mutant, suggesting that impaired genome integrity may also have challenged the stem cell activity. Genetic interaction analysis reveals that SDG2 and CHROMATIN ASSEMBLY FACTOR-1 act synergistically in root SCN and genome integrity maintenance but not in telomere length maintenance. We conclude that SDG2-mediated H3K4me3 plays a distinctive role in the regulation of chromatin structure and genome integrity, which are key features in pluripotency of stem cells and crucial for root growth and development.
Highlights
During multicellular organism development, each cell type elaborates a specific developmental program, and the acquired cell fate needs to be stably maintained
Our results indicate that SET DOMAIN GROUP 2 (SDG2) function is required for stem cell niche (SCN) establishment for lateral root (LR) development and is critical for stable maintenance of SCN organization and function in primary roots
We provide evidence that Trithorax group (TrxG) gene and H3K4me3 play crucial roles in root stem cell fate establishment and maintenance during plant postembryonic development
Summary
Each cell type elaborates a specific developmental program, and the acquired cell fate needs to be stably maintained. The well-defined and rather stereotypical cell organization of Arabidopsis roots makes it an excellent experimental system to study cell fate maintenance and cell differentiation [1,2]. The root meristem contains four types of stem cells: epidermis/lateral root cap initials, cortex/endodermis initials, stele initials, and columella root cap initials. These stem cells surround the quiescent centre (QC), which is composed of a small number of mitotically lessactive cells, together forming the root stem cell niche (SCN). QC promotes the continuous cell division of the initial cells and provides short-range signals to prevent stem cells from differentiation [3]
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