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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

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.


Root hair length and density in response to Cd and As(III) in ttg1 Arabidopsis.(A) Diagram showing T-DNA insertion position in ttg1 Arabidopsis. (B) Left, semi-quantitative RT-PCR products (transcript levels) of AtTTG1 in control (Col-0) and ttg1 Arabidopsis. PCR product of actin (AtActin) was used as a loading control; Right, real-time PCR results. (C) Morphology of ttg1 Arabidopsis (1-week-old) seedlings germinated and grown on 1/2 MS agar plates containing no metal (left), 40 μM CdSO4 (center), and 10 μM AsNaO2 (right). (D) Quantification of the primary root length of ttg1 Arabidopsis shown in (C). (E) Root hair morphology of ttg1 Arabidopsis germinated and grown on 1/2 MS with no metal (left), 40 μM CdSO4 (center) and 10 μM As(ø) (right). Roots were observed at 40× magnification; scale bars = 0.2 mm. (F) Graphs representing root hair density in a 5 mm section from the starting point of differentiation zone in ttg1 Arabidopsis shown in (E). (G) Graphs representing root hair length in a 5 mm section from the starting point of differentiation zone in ttg1 Arabidopsis shown in (E). Values are average (±SE) of three independent experiments, each involving 10 seedlings. Different letters over each column indicate a significant difference according to Tukey’s multiple comparison test (p ≤ 0.01).
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Figure 5: Root hair length and density in response to Cd and As(III) in ttg1 Arabidopsis.(A) Diagram showing T-DNA insertion position in ttg1 Arabidopsis. (B) Left, semi-quantitative RT-PCR products (transcript levels) of AtTTG1 in control (Col-0) and ttg1 Arabidopsis. PCR product of actin (AtActin) was used as a loading control; Right, real-time PCR results. (C) Morphology of ttg1 Arabidopsis (1-week-old) seedlings germinated and grown on 1/2 MS agar plates containing no metal (left), 40 μM CdSO4 (center), and 10 μM AsNaO2 (right). (D) Quantification of the primary root length of ttg1 Arabidopsis shown in (C). (E) Root hair morphology of ttg1 Arabidopsis germinated and grown on 1/2 MS with no metal (left), 40 μM CdSO4 (center) and 10 μM As(ø) (right). Roots were observed at 40× magnification; scale bars = 0.2 mm. (F) Graphs representing root hair density in a 5 mm section from the starting point of differentiation zone in ttg1 Arabidopsis shown in (E). (G) Graphs representing root hair length in a 5 mm section from the starting point of differentiation zone in ttg1 Arabidopsis shown in (E). Values are average (±SE) of three independent experiments, each involving 10 seedlings. Different letters over each column indicate a significant difference according to Tukey’s multiple comparison test (p ≤ 0.01).

Mentions: The effects of Cd and As(III) on root hair development were also examined in the ttg1 (negative regulator of root hair differentiation) mutant (Figure 5). ttg1 Arabidopsis (SALK_ 054584, Figure 5A) showed extremely low expression of AtTTG1 (Figure 5B) and a decrease in root length in response to Cd and As(III) (Figures 5C,D). As shown in Figures 5E,F, root hair density was higher in ttg1 Arabidopsis plants than in control plants in 1/2 MS media, which is consistent with the role of TTG1 as a negative regulator of root hair fate determination. However, root hair density was not enhanced by Cd and As(III), suggesting that the root hairs of the ttg1 mutant were already fully differentiated to the level of metal-treated Col-0. By contrast, root hair length was slightly shorter in the ttg1 mutant than in Col-0 in 1/2 MS medium, and it was increased by Cd and As(III) to the level of metal-treated Col-0. This implied that root hair differentiation was promoted, whereas root hair elongation was not enhanced in ttg1, confirming that TTG1 is a negative regulator of root hair differentiation but not of root hair elongation.


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
Root hair length and density in response to Cd and As(III) in ttg1 Arabidopsis.(A) Diagram showing T-DNA insertion position in ttg1 Arabidopsis. (B) Left, semi-quantitative RT-PCR products (transcript levels) of AtTTG1 in control (Col-0) and ttg1 Arabidopsis. PCR product of actin (AtActin) was used as a loading control; Right, real-time PCR results. (C) Morphology of ttg1 Arabidopsis (1-week-old) seedlings germinated and grown on 1/2 MS agar plates containing no metal (left), 40 μM CdSO4 (center), and 10 μM AsNaO2 (right). (D) Quantification of the primary root length of ttg1 Arabidopsis shown in (C). (E) Root hair morphology of ttg1 Arabidopsis germinated and grown on 1/2 MS with no metal (left), 40 μM CdSO4 (center) and 10 μM As(ø) (right). Roots were observed at 40× magnification; scale bars = 0.2 mm. (F) Graphs representing root hair density in a 5 mm section from the starting point of differentiation zone in ttg1 Arabidopsis shown in (E). (G) Graphs representing root hair length in a 5 mm section from the starting point of differentiation zone in ttg1 Arabidopsis shown in (E). Values are average (±SE) of three independent experiments, each involving 10 seedlings. Different letters over each column indicate a significant difference according to Tukey’s multiple comparison test (p ≤ 0.01).
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Figure 5: Root hair length and density in response to Cd and As(III) in ttg1 Arabidopsis.(A) Diagram showing T-DNA insertion position in ttg1 Arabidopsis. (B) Left, semi-quantitative RT-PCR products (transcript levels) of AtTTG1 in control (Col-0) and ttg1 Arabidopsis. PCR product of actin (AtActin) was used as a loading control; Right, real-time PCR results. (C) Morphology of ttg1 Arabidopsis (1-week-old) seedlings germinated and grown on 1/2 MS agar plates containing no metal (left), 40 μM CdSO4 (center), and 10 μM AsNaO2 (right). (D) Quantification of the primary root length of ttg1 Arabidopsis shown in (C). (E) Root hair morphology of ttg1 Arabidopsis germinated and grown on 1/2 MS with no metal (left), 40 μM CdSO4 (center) and 10 μM As(ø) (right). Roots were observed at 40× magnification; scale bars = 0.2 mm. (F) Graphs representing root hair density in a 5 mm section from the starting point of differentiation zone in ttg1 Arabidopsis shown in (E). (G) Graphs representing root hair length in a 5 mm section from the starting point of differentiation zone in ttg1 Arabidopsis shown in (E). Values are average (±SE) of three independent experiments, each involving 10 seedlings. Different letters over each column indicate a significant difference according to Tukey’s multiple comparison test (p ≤ 0.01).
Mentions: The effects of Cd and As(III) on root hair development were also examined in the ttg1 (negative regulator of root hair differentiation) mutant (Figure 5). ttg1 Arabidopsis (SALK_ 054584, Figure 5A) showed extremely low expression of AtTTG1 (Figure 5B) and a decrease in root length in response to Cd and As(III) (Figures 5C,D). As shown in Figures 5E,F, root hair density was higher in ttg1 Arabidopsis plants than in control plants in 1/2 MS media, which is consistent with the role of TTG1 as a negative regulator of root hair fate determination. However, root hair density was not enhanced by Cd and As(III), suggesting that the root hairs of the ttg1 mutant were already fully differentiated to the level of metal-treated Col-0. By contrast, root hair length was slightly shorter in the ttg1 mutant than in Col-0 in 1/2 MS medium, and it was increased by Cd and As(III) to the level of metal-treated Col-0. This implied that root hair differentiation was promoted, whereas root hair elongation was not enhanced in ttg1, confirming that TTG1 is a negative regulator of root hair differentiation but not of root hair elongation.

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.