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Coordination between zinc and phosphate homeostasis involves the transcription factor PHR1, the phosphate exporter PHO1, and its homologue PHO1;H3 in Arabidopsis.

Khan GA, Bouraine S, Wege S, Li Y, de Carbonnel M, Berthomieu P, Poirier Y, Rouached H - J. Exp. Bot. (2014)

Bottom Line: This work aimed at examining the effects of Zn deficiency on Pi accumulation in Arabidopsis thaliana and uncovering genes involved in the Zn-Pi synergy.Zn deprivation had a very limited effect on transcript levels of Pi-starvation-responsive genes such as AT4, IPS1, and microRNA399, or on of members of the high-affinity Pi transporter family PHT1.This was, however, not observed in a pho1 pho1;h3 double mutant, suggesting that PHO1;H3 restricts root-to-shoot Pi transfer requiring PHO1 function for Pi homeostasis in response to Zn deficiency.

View Article: PubMed Central - PubMed

Affiliation: Département de Biologie Moléculaire Végétale, Biophore, Université de Lausanne, CH-1015 Lausanne, Switzerland.

ABSTRACT
Interactions between zinc (Zn) and phosphate (Pi) nutrition in plants have long been recognized, but little information is available on their molecular bases and biological significance. This work aimed at examining the effects of Zn deficiency on Pi accumulation in Arabidopsis thaliana and uncovering genes involved in the Zn-Pi synergy. Wild-type plants as well as mutants affected in Pi signalling and transport genes, namely the transcription factor PHR1, the E2-conjugase PHO2, and the Pi exporter PHO1, were examined. Zn deficiency caused an increase in shoot Pi content in the wild type as well as in the pho2 mutant, but not in the phr1 or pho1 mutants. This indicated that PHR1 and PHO1 participate in the coregulation of Zn and Pi homeostasis. Zn deprivation had a very limited effect on transcript levels of Pi-starvation-responsive genes such as AT4, IPS1, and microRNA399, or on of members of the high-affinity Pi transporter family PHT1. Interestingly, one of the PHO1 homologues, PHO1;H3, was upregulated in response to Zn deficiency. The expression pattern of PHO1 and PHO1;H3 were similar, both being expressed in cells of the root vascular cylinder and both localized to the Golgi when expressed transiently in tobacco cells. When grown in Zn-free medium, pho1;h3 mutant plants displayed higher Pi contents in the shoots than wild-type plants. This was, however, not observed in a pho1 pho1;h3 double mutant, suggesting that PHO1;H3 restricts root-to-shoot Pi transfer requiring PHO1 function for Pi homeostasis in response to Zn deficiency.

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Expression pattern of PHO1;H3-GFP in Arabidopsis. pho1;h3 mutant was transformed with a PHO1;H3-GFP fusion construct expressed under the PHO1;H3 promoter and fluorescence examined in roots (A–C) and cotyledons (D–F) of 5-d-old seedlings. (A) PHO1;H3-GFP expression (green) in roots, (B) propidium iodine staining of the cell wall of root epidermal and cortical cells (magenta), and (C) overlay of A and B. (D) PHO1;H3-GFP expression (green) in epidermal cells of cotyledon, (E) transmission image, and (F) overlay of D and E. Bars = 20 μm.
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Figure 6: Expression pattern of PHO1;H3-GFP in Arabidopsis. pho1;h3 mutant was transformed with a PHO1;H3-GFP fusion construct expressed under the PHO1;H3 promoter and fluorescence examined in roots (A–C) and cotyledons (D–F) of 5-d-old seedlings. (A) PHO1;H3-GFP expression (green) in roots, (B) propidium iodine staining of the cell wall of root epidermal and cortical cells (magenta), and (C) overlay of A and B. (D) PHO1;H3-GFP expression (green) in epidermal cells of cotyledon, (E) transmission image, and (F) overlay of D and E. Bars = 20 μm.

Mentions: The expression pattern of PHO1;H3 was also analysed in transgenic pho1;h3 mutant plants expressing PHO1;H3 fused with GFP under control of its native promoter. In the root, PHO1;H3::GFP was primarily detected in cells of the vascular cylinder (Fig. 6A–C). In cotyledons, some weak expression was also observed in epidermal cells (Fig. 6D–F). At the subcellular level, PHO1;H3-GFP expression was found associated with punctate bodies. Attempts to colocalize the fluorescence pattern to particular subcellular compartments in Arabidopsis failed due to a combination of the relatively weak expression and difficulties in obtaining adequate resolution. As an alternative, the subcellular localization of PHO1;H3-GFP was assessed via transient expression in tobacco (N. benthamiana) leaves that were coinfiltrated with various subcellular markers. PHO1;H3-GFP did not colocalize with either the plasma membrane marker CBL1-OFP or the endoplasmic reticulum marker ER-rk-mCherry (Fig. 7A, B). Extensive colocalization was however observed with the Golgi marker ManI-RFP (Fig. 7C). In contrast, more limited colocalization was observed with the trans-Golgi (TGN) marker RFP-Syp61 (Fig. 7D). Since PHO1-GFP has previously been shown to localize to the Golgi and TGN in tobacco leaves (Arpat et al., 2012), the colocalization of PHO1;H3-GFP and PHO1-RFP was analysed. The fluorescent bodies associated with PHO1;H3-GFP largely overlapped with a subset of PHO1-RFP fluorescent bodies (Fig. 7E). This pattern of overlap likely reflected the stronger association of PHO1:H3 to the Golgi while PHO1-RFP is more equally distributed to the Golgi and TGN (Arpat et al., 2012). Overall, these results revealed that PHO1;H3 and PHO1 share similar and overlapping tissue and subcellular localization (Hamburger et al., 2002; Arpat et al., 2012). The specific upregulation of PHO1;H3 under Zn deficiency, its homology with PHO1, and the colocalization of PHO1 and PHO1;H3 suggest a potential implication of PHO1;H3 in the regulation of Pi homeostasis in response to Zn deficiency.


Coordination between zinc and phosphate homeostasis involves the transcription factor PHR1, the phosphate exporter PHO1, and its homologue PHO1;H3 in Arabidopsis.

Khan GA, Bouraine S, Wege S, Li Y, de Carbonnel M, Berthomieu P, Poirier Y, Rouached H - J. Exp. Bot. (2014)

Expression pattern of PHO1;H3-GFP in Arabidopsis. pho1;h3 mutant was transformed with a PHO1;H3-GFP fusion construct expressed under the PHO1;H3 promoter and fluorescence examined in roots (A–C) and cotyledons (D–F) of 5-d-old seedlings. (A) PHO1;H3-GFP expression (green) in roots, (B) propidium iodine staining of the cell wall of root epidermal and cortical cells (magenta), and (C) overlay of A and B. (D) PHO1;H3-GFP expression (green) in epidermal cells of cotyledon, (E) transmission image, and (F) overlay of D and E. Bars = 20 μm.
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Figure 6: Expression pattern of PHO1;H3-GFP in Arabidopsis. pho1;h3 mutant was transformed with a PHO1;H3-GFP fusion construct expressed under the PHO1;H3 promoter and fluorescence examined in roots (A–C) and cotyledons (D–F) of 5-d-old seedlings. (A) PHO1;H3-GFP expression (green) in roots, (B) propidium iodine staining of the cell wall of root epidermal and cortical cells (magenta), and (C) overlay of A and B. (D) PHO1;H3-GFP expression (green) in epidermal cells of cotyledon, (E) transmission image, and (F) overlay of D and E. Bars = 20 μm.
Mentions: The expression pattern of PHO1;H3 was also analysed in transgenic pho1;h3 mutant plants expressing PHO1;H3 fused with GFP under control of its native promoter. In the root, PHO1;H3::GFP was primarily detected in cells of the vascular cylinder (Fig. 6A–C). In cotyledons, some weak expression was also observed in epidermal cells (Fig. 6D–F). At the subcellular level, PHO1;H3-GFP expression was found associated with punctate bodies. Attempts to colocalize the fluorescence pattern to particular subcellular compartments in Arabidopsis failed due to a combination of the relatively weak expression and difficulties in obtaining adequate resolution. As an alternative, the subcellular localization of PHO1;H3-GFP was assessed via transient expression in tobacco (N. benthamiana) leaves that were coinfiltrated with various subcellular markers. PHO1;H3-GFP did not colocalize with either the plasma membrane marker CBL1-OFP or the endoplasmic reticulum marker ER-rk-mCherry (Fig. 7A, B). Extensive colocalization was however observed with the Golgi marker ManI-RFP (Fig. 7C). In contrast, more limited colocalization was observed with the trans-Golgi (TGN) marker RFP-Syp61 (Fig. 7D). Since PHO1-GFP has previously been shown to localize to the Golgi and TGN in tobacco leaves (Arpat et al., 2012), the colocalization of PHO1;H3-GFP and PHO1-RFP was analysed. The fluorescent bodies associated with PHO1;H3-GFP largely overlapped with a subset of PHO1-RFP fluorescent bodies (Fig. 7E). This pattern of overlap likely reflected the stronger association of PHO1:H3 to the Golgi while PHO1-RFP is more equally distributed to the Golgi and TGN (Arpat et al., 2012). Overall, these results revealed that PHO1;H3 and PHO1 share similar and overlapping tissue and subcellular localization (Hamburger et al., 2002; Arpat et al., 2012). The specific upregulation of PHO1;H3 under Zn deficiency, its homology with PHO1, and the colocalization of PHO1 and PHO1;H3 suggest a potential implication of PHO1;H3 in the regulation of Pi homeostasis in response to Zn deficiency.

Bottom Line: This work aimed at examining the effects of Zn deficiency on Pi accumulation in Arabidopsis thaliana and uncovering genes involved in the Zn-Pi synergy.Zn deprivation had a very limited effect on transcript levels of Pi-starvation-responsive genes such as AT4, IPS1, and microRNA399, or on of members of the high-affinity Pi transporter family PHT1.This was, however, not observed in a pho1 pho1;h3 double mutant, suggesting that PHO1;H3 restricts root-to-shoot Pi transfer requiring PHO1 function for Pi homeostasis in response to Zn deficiency.

View Article: PubMed Central - PubMed

Affiliation: Département de Biologie Moléculaire Végétale, Biophore, Université de Lausanne, CH-1015 Lausanne, Switzerland.

ABSTRACT
Interactions between zinc (Zn) and phosphate (Pi) nutrition in plants have long been recognized, but little information is available on their molecular bases and biological significance. This work aimed at examining the effects of Zn deficiency on Pi accumulation in Arabidopsis thaliana and uncovering genes involved in the Zn-Pi synergy. Wild-type plants as well as mutants affected in Pi signalling and transport genes, namely the transcription factor PHR1, the E2-conjugase PHO2, and the Pi exporter PHO1, were examined. Zn deficiency caused an increase in shoot Pi content in the wild type as well as in the pho2 mutant, but not in the phr1 or pho1 mutants. This indicated that PHR1 and PHO1 participate in the coregulation of Zn and Pi homeostasis. Zn deprivation had a very limited effect on transcript levels of Pi-starvation-responsive genes such as AT4, IPS1, and microRNA399, or on of members of the high-affinity Pi transporter family PHT1. Interestingly, one of the PHO1 homologues, PHO1;H3, was upregulated in response to Zn deficiency. The expression pattern of PHO1 and PHO1;H3 were similar, both being expressed in cells of the root vascular cylinder and both localized to the Golgi when expressed transiently in tobacco cells. When grown in Zn-free medium, pho1;h3 mutant plants displayed higher Pi contents in the shoots than wild-type plants. This was, however, not observed in a pho1 pho1;h3 double mutant, suggesting that PHO1;H3 restricts root-to-shoot Pi transfer requiring PHO1 function for Pi homeostasis in response to Zn deficiency.

Show MeSH
Related in: MedlinePlus