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SDG2-mediated H3K4 methylation is required for proper Arabidopsis root growth and development.

Yao X, Feng H, Yu Y, Dong A, Shen WH - PLoS ONE (2013)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Genetic Engineering, International Associated Laboratory of CNRS-Fudan-HUNAU on Plant Epigenome Research, School of Life Sciences, Fudan University, Shanghai, PR China.

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.

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Loss of SDG2 impairs the primary root stem cell niche maintenance. Aand B, Comparison of primary root apical meristem sizes between wild-type Col and the mutant sdg2-3, respectively. DIC images were taken on the roots of 6-day-old seedlings. Arrowheads indicate positions of the transition from meristem to elongation zone. Bar = 100µm. C and D, Comparison of QC25:GUS expression and root cap cell layer organization between Col and sdg2-3, respectively. DIC images were taken on GUS- and Lugol-stained root tips of 6-day-old seedlings. Arrowheads indicate the columella initial cell layer. Bar = 20 µm. E and F, Comparison of cell layer organization of root apical meristem between Col and sdg2-3, respectively. Confocal images were taken on PI-stained roots of 6-day-old seedlings. Bar = 50 µm. The close-up regions are shown by color indication of different cell types: QC cell in blue, columella root cap and columella initial cells in rose, lateral root cap cells in sky-blue, epidermal cells and epidermis/lateral root cap initials in red, cortex cells in green, endodermal cells in yellow, cortex/endodermis initials in purple, stele cells and stele initials in gray. G and H, Comparison of cell layer organizations of root apical meristem between Col and sdg2-3, respectively. Confocal images were taken on PI-stained roots of 14-day-old seedlings. Bar = 50 µm. The close-up regions are shown with colorations as described in E and F.
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pone-0056537-g003: Loss of SDG2 impairs the primary root stem cell niche maintenance. Aand B, Comparison of primary root apical meristem sizes between wild-type Col and the mutant sdg2-3, respectively. DIC images were taken on the roots of 6-day-old seedlings. Arrowheads indicate positions of the transition from meristem to elongation zone. Bar = 100µm. C and D, Comparison of QC25:GUS expression and root cap cell layer organization between Col and sdg2-3, respectively. DIC images were taken on GUS- and Lugol-stained root tips of 6-day-old seedlings. Arrowheads indicate the columella initial cell layer. Bar = 20 µm. E and F, Comparison of cell layer organization of root apical meristem between Col and sdg2-3, respectively. Confocal images were taken on PI-stained roots of 6-day-old seedlings. Bar = 50 µm. The close-up regions are shown by color indication of different cell types: QC cell in blue, columella root cap and columella initial cells in rose, lateral root cap cells in sky-blue, epidermal cells and epidermis/lateral root cap initials in red, cortex cells in green, endodermal cells in yellow, cortex/endodermis initials in purple, stele cells and stele initials in gray. G and H, Comparison of cell layer organizations of root apical meristem between Col and sdg2-3, respectively. Confocal images were taken on PI-stained roots of 14-day-old seedlings. Bar = 50 µm. The close-up regions are shown with colorations as described in E and F.

Mentions: We further examined SCN organization in the primary roots. Consistent with the short-root phenotype, the size of the root apical meristem (RAM) was reduced in sdg2-3 compared to WT (Figure 3A and 3B). A close examination of the root tip revealed that WT roots contain the regular and arc-shaped arrangement of the four layers of starch granule-rich columella cells and a layer of starch granule-lacking columella initial cells located under the QC layer (Figure 3C). In sdg2-3 roots, the columella cells were displayed in disorganized cell layers and starch granules were observed in cells adjacent to QC (Figure 3D), indicating a loss of columella initial cell identity. In addition, expression of the QC specific marker QC25:GUS[44] was detected at lower levels and in a fewer number of cells in sdg2-3 compared to WT roots (Figure 3C, D). Further propidium iodide (PI) staining and microscopy analysis revealed that, compared with WT (Figure 3E), the sdg2-3 mutant contains a disorganized SCN with reduced number of QC cells, fewer and less recognizable stem cells of stele initials, as well as fewer cortex/endodermis initials, epidermis initials, and columella root cap initials (Figure 3F). The cell size was also largely more variable, with either increased or reduced volume, in each type of cells within SCN of sdg2-3 as compared to WT. As compared to the so far described defects in the primary roots of 6-day-old sdg2-3 seedlings, the primary roots of 14-day-old sdg2-3 seedlings showed similar SCN defects but to a more severe degree (Figure 3H), whereas the regular SCN organization in WT was stably maintained (Figure 3G). It appears that during postembryonic seedling growth the sdg2-3 root SCN gradually loses cell identity and stem cell function, causing root growth arrest.


SDG2-mediated H3K4 methylation is required for proper Arabidopsis root growth and development.

Yao X, Feng H, Yu Y, Dong A, Shen WH - PLoS ONE (2013)

Loss of SDG2 impairs the primary root stem cell niche maintenance. Aand B, Comparison of primary root apical meristem sizes between wild-type Col and the mutant sdg2-3, respectively. DIC images were taken on the roots of 6-day-old seedlings. Arrowheads indicate positions of the transition from meristem to elongation zone. Bar = 100µm. C and D, Comparison of QC25:GUS expression and root cap cell layer organization between Col and sdg2-3, respectively. DIC images were taken on GUS- and Lugol-stained root tips of 6-day-old seedlings. Arrowheads indicate the columella initial cell layer. Bar = 20 µm. E and F, Comparison of cell layer organization of root apical meristem between Col and sdg2-3, respectively. Confocal images were taken on PI-stained roots of 6-day-old seedlings. Bar = 50 µm. The close-up regions are shown by color indication of different cell types: QC cell in blue, columella root cap and columella initial cells in rose, lateral root cap cells in sky-blue, epidermal cells and epidermis/lateral root cap initials in red, cortex cells in green, endodermal cells in yellow, cortex/endodermis initials in purple, stele cells and stele initials in gray. G and H, Comparison of cell layer organizations of root apical meristem between Col and sdg2-3, respectively. Confocal images were taken on PI-stained roots of 14-day-old seedlings. Bar = 50 µm. The close-up regions are shown with colorations as described in E and F.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585709&req=5

pone-0056537-g003: Loss of SDG2 impairs the primary root stem cell niche maintenance. Aand B, Comparison of primary root apical meristem sizes between wild-type Col and the mutant sdg2-3, respectively. DIC images were taken on the roots of 6-day-old seedlings. Arrowheads indicate positions of the transition from meristem to elongation zone. Bar = 100µm. C and D, Comparison of QC25:GUS expression and root cap cell layer organization between Col and sdg2-3, respectively. DIC images were taken on GUS- and Lugol-stained root tips of 6-day-old seedlings. Arrowheads indicate the columella initial cell layer. Bar = 20 µm. E and F, Comparison of cell layer organization of root apical meristem between Col and sdg2-3, respectively. Confocal images were taken on PI-stained roots of 6-day-old seedlings. Bar = 50 µm. The close-up regions are shown by color indication of different cell types: QC cell in blue, columella root cap and columella initial cells in rose, lateral root cap cells in sky-blue, epidermal cells and epidermis/lateral root cap initials in red, cortex cells in green, endodermal cells in yellow, cortex/endodermis initials in purple, stele cells and stele initials in gray. G and H, Comparison of cell layer organizations of root apical meristem between Col and sdg2-3, respectively. Confocal images were taken on PI-stained roots of 14-day-old seedlings. Bar = 50 µm. The close-up regions are shown with colorations as described in E and F.
Mentions: We further examined SCN organization in the primary roots. Consistent with the short-root phenotype, the size of the root apical meristem (RAM) was reduced in sdg2-3 compared to WT (Figure 3A and 3B). A close examination of the root tip revealed that WT roots contain the regular and arc-shaped arrangement of the four layers of starch granule-rich columella cells and a layer of starch granule-lacking columella initial cells located under the QC layer (Figure 3C). In sdg2-3 roots, the columella cells were displayed in disorganized cell layers and starch granules were observed in cells adjacent to QC (Figure 3D), indicating a loss of columella initial cell identity. In addition, expression of the QC specific marker QC25:GUS[44] was detected at lower levels and in a fewer number of cells in sdg2-3 compared to WT roots (Figure 3C, D). Further propidium iodide (PI) staining and microscopy analysis revealed that, compared with WT (Figure 3E), the sdg2-3 mutant contains a disorganized SCN with reduced number of QC cells, fewer and less recognizable stem cells of stele initials, as well as fewer cortex/endodermis initials, epidermis initials, and columella root cap initials (Figure 3F). The cell size was also largely more variable, with either increased or reduced volume, in each type of cells within SCN of sdg2-3 as compared to WT. As compared to the so far described defects in the primary roots of 6-day-old sdg2-3 seedlings, the primary roots of 14-day-old sdg2-3 seedlings showed similar SCN defects but to a more severe degree (Figure 3H), whereas the regular SCN organization in WT was stably maintained (Figure 3G). It appears that during postembryonic seedling growth the sdg2-3 root SCN gradually loses cell identity and stem cell function, causing root growth arrest.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Genetic Engineering, International Associated Laboratory of CNRS-Fudan-HUNAU on Plant Epigenome Research, School of Life Sciences, Fudan University, Shanghai, PR China.

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.

Show MeSH
Related in: MedlinePlus