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The Density and Length of Root Hairs Are Enhanced in Response to Cadmium and Arsenic by Modulating Gene Expressions Involved in Fate Determination and Morphogenesis of Root Hairs in Arabidopsis

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ABSTRACT

Root hairs are tubular outgrowths that originate from epidermal cells. Exposure of Arabidopsis to cadmium (Cd) and arsenic [arsenite, As(III)] increases root hair density and length. To examine the underlying mechanism, we measured the expression of genes involved in fate determination and morphogenesis of root hairs. Cd and As(III) downregulated TTG1 and GL2 (negative regulators of fate determination) and upregulated GEM (positive regulator), suggesting that root hair fate determination is stimulated by Cd and As(III). Cd and As(III) increased the transcript levels of genes involved in root hair initiation (RHD6 and AXR2) and root hair elongation (AUX1, AXR1, ETR1, and EIN2) except CTR1. DR5::GUS transgenic Arabidopsis showed a higher DR5 expression in the root tip, suggesting that Cd and As(III) increased the auxin content in the root tip. Knockdown of TTG1 in Arabidopsis resulted in increased root hair density and decreased root hair length compared with the control (Col-0) on 1/2 MS media. This phenotype may be attributed to the downregulation of GL2 and CTR1 and upregulation of RHD6. By contrast, gem mutant plants displayed a decrease in root hair density and length with reduced expression of RHD6, AXR2, AUX1, AXR1, ETR1, CTR1, and EIN2. Taken together, our results indicate that fate determination, initiation, and elongation of root hairs are stimulated in response to Cd and As(III) through the modulation of the expression of genes involved in these processes in Arabidopsis.

No MeSH data available.


Effect of Cd and As(III) on expressions of genes participated in the differentiation (fate determination) and elongation of root hairs in ttg1 Arabidopsis.(A) Semi-quantitative RT-PCR results showing relative transcript levels of various genes involved in the differentiation (GL2), initiation (RHD6 and AXR2) and elongation (AUX1, AXR1, ETR1, CTR1, and EIN2) of root hairs in Col-0 and ttg1 Arabidopsis. RT-PCR was performed using total RNA isolated from 1-week old plants which were germinated and grown on 1/2 MS agar media treated with no metal, 40 μM CdSO4 and 10 μM As(III). The gel photography represents three experimental replicates. (B) Quantitative real-time PCR results of various genes involved in root hair differentiation and elongation shown in (A). Transcript levels were normalized to the transcript level of Actin.
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Figure 6: Effect of Cd and As(III) on expressions of genes participated in the differentiation (fate determination) and elongation of root hairs in ttg1 Arabidopsis.(A) Semi-quantitative RT-PCR results showing relative transcript levels of various genes involved in the differentiation (GL2), initiation (RHD6 and AXR2) and elongation (AUX1, AXR1, ETR1, CTR1, and EIN2) of root hairs in Col-0 and ttg1 Arabidopsis. RT-PCR was performed using total RNA isolated from 1-week old plants which were germinated and grown on 1/2 MS agar media treated with no metal, 40 μM CdSO4 and 10 μM As(III). The gel photography represents three experimental replicates. (B) Quantitative real-time PCR results of various genes involved in root hair differentiation and elongation shown in (A). Transcript levels were normalized to the transcript level of Actin.

Mentions: To understand the molecular mechanism underlying the enhanced root hair density and slightly reduced root hair length in ttg1 plants, the expression of genes involved in fate determination, initiation, and elongation of root hairs was examined (Figure 6 and Supplementary Figure S2). The expression of GL2, which was reported as a negative regulator of root hair fate determination, was repressed and not induced by Cd and As(III). This result supports previous reports that GL2 is induced by TTG1, resulting in the suppression of root hair differentiation (Hung et al., 1998). In addition, the expression of RHD6, which is inhibited by GL2 and involved in root hair initiation (Masucci and Schiefelbein, 1996), was upregulated in ttg1 plants and this effect was enhanced by Cd and As(III). However, AXR2 expression was not increased in ttg1 plants, despite the fact that the axr2 mutant has a lower number of root hairs (Masucci and Schiefelbein, 1996), implying that AXR2 is involved in root hair initiation similar to RHD6. The expression of auxin/ethylene signaling genes (AUX1, AXR1, ETR1, CTR1, and EIN2) involved in root hair elongation in ttg1 plants was similar to that in Col-0 plants, confirming that auxin/ethylene signaling genes are not controlled by TTG1/GL2. However, it was not clear why root hair length was shorter in ttg1 than in Col-0, since the expression of root hair elongation genes was not decreased. Regarding root hair initiation and elongation in response to Cd and As(III), similar to Col-0, the expression of genes involved in root hair initiation (RHD6 and AXR2) and elongation (AUX1, AXR1, ETR1, and EIN2) was increased, while CTR1 expression was reduced.


The Density and Length of Root Hairs Are Enhanced in Response to Cadmium and Arsenic by Modulating Gene Expressions Involved in Fate Determination and Morphogenesis of Root Hairs in Arabidopsis
Effect of Cd and As(III) on expressions of genes participated in the differentiation (fate determination) and elongation of root hairs in ttg1 Arabidopsis.(A) Semi-quantitative RT-PCR results showing relative transcript levels of various genes involved in the differentiation (GL2), initiation (RHD6 and AXR2) and elongation (AUX1, AXR1, ETR1, CTR1, and EIN2) of root hairs in Col-0 and ttg1 Arabidopsis. RT-PCR was performed using total RNA isolated from 1-week old plants which were germinated and grown on 1/2 MS agar media treated with no metal, 40 μM CdSO4 and 10 μM As(III). The gel photography represents three experimental replicates. (B) Quantitative real-time PCR results of various genes involved in root hair differentiation and elongation shown in (A). Transcript levels were normalized to the transcript level of Actin.
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Figure 6: Effect of Cd and As(III) on expressions of genes participated in the differentiation (fate determination) and elongation of root hairs in ttg1 Arabidopsis.(A) Semi-quantitative RT-PCR results showing relative transcript levels of various genes involved in the differentiation (GL2), initiation (RHD6 and AXR2) and elongation (AUX1, AXR1, ETR1, CTR1, and EIN2) of root hairs in Col-0 and ttg1 Arabidopsis. RT-PCR was performed using total RNA isolated from 1-week old plants which were germinated and grown on 1/2 MS agar media treated with no metal, 40 μM CdSO4 and 10 μM As(III). The gel photography represents three experimental replicates. (B) Quantitative real-time PCR results of various genes involved in root hair differentiation and elongation shown in (A). Transcript levels were normalized to the transcript level of Actin.
Mentions: To understand the molecular mechanism underlying the enhanced root hair density and slightly reduced root hair length in ttg1 plants, the expression of genes involved in fate determination, initiation, and elongation of root hairs was examined (Figure 6 and Supplementary Figure S2). The expression of GL2, which was reported as a negative regulator of root hair fate determination, was repressed and not induced by Cd and As(III). This result supports previous reports that GL2 is induced by TTG1, resulting in the suppression of root hair differentiation (Hung et al., 1998). In addition, the expression of RHD6, which is inhibited by GL2 and involved in root hair initiation (Masucci and Schiefelbein, 1996), was upregulated in ttg1 plants and this effect was enhanced by Cd and As(III). However, AXR2 expression was not increased in ttg1 plants, despite the fact that the axr2 mutant has a lower number of root hairs (Masucci and Schiefelbein, 1996), implying that AXR2 is involved in root hair initiation similar to RHD6. The expression of auxin/ethylene signaling genes (AUX1, AXR1, ETR1, CTR1, and EIN2) involved in root hair elongation in ttg1 plants was similar to that in Col-0 plants, confirming that auxin/ethylene signaling genes are not controlled by TTG1/GL2. However, it was not clear why root hair length was shorter in ttg1 than in Col-0, since the expression of root hair elongation genes was not decreased. Regarding root hair initiation and elongation in response to Cd and As(III), similar to Col-0, the expression of genes involved in root hair initiation (RHD6 and AXR2) and elongation (AUX1, AXR1, ETR1, and EIN2) was increased, while CTR1 expression was reduced.

View Article: PubMed Central - PubMed

ABSTRACT

Root hairs are tubular outgrowths that originate from epidermal cells. Exposure of Arabidopsis to cadmium (Cd) and arsenic [arsenite, As(III)] increases root hair density and length. To examine the underlying mechanism, we measured the expression of genes involved in fate determination and morphogenesis of root hairs. Cd and As(III) downregulated TTG1 and GL2 (negative regulators of fate determination) and upregulated GEM (positive regulator), suggesting that root hair fate determination is stimulated by Cd and As(III). Cd and As(III) increased the transcript levels of genes involved in root hair initiation (RHD6 and AXR2) and root hair elongation (AUX1, AXR1, ETR1, and EIN2) except CTR1. DR5::GUS transgenic Arabidopsis showed a higher DR5 expression in the root tip, suggesting that Cd and As(III) increased the auxin content in the root tip. Knockdown of TTG1 in Arabidopsis resulted in increased root hair density and decreased root hair length compared with the control (Col-0) on 1/2 MS media. This phenotype may be attributed to the downregulation of GL2 and CTR1 and upregulation of RHD6. By contrast, gem mutant plants displayed a decrease in root hair density and length with reduced expression of RHD6, AXR2, AUX1, AXR1, ETR1, CTR1, and EIN2. Taken together, our results indicate that fate determination, initiation, and elongation of root hairs are stimulated in response to Cd and As(III) through the modulation of the expression of genes involved in these processes in Arabidopsis.

No MeSH data available.