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A novel role for the root cap in phosphate uptake and homeostasis.

Kanno S, Arrighi JF, Chiarenza S, Bayle V, Berthomé R, Péret B, Javot H, Delannoy E, Marin E, Nakanishi TM, Thibaud MC, Nussaume L - Elife (2016)

Bottom Line: Remarkably, the diminutive size of the root cap cells at the root-to-soil exchange surface accounts for a significant amount of the total seedling phosphate uptake (approximately 20%).This level of Pi absorption is sufficient for shoot biomass production (up to a 180% gain in soil), as well as repression of Pi starvation-induced genes.These results extend our understanding of this important tissue from its previously described roles in environmental perception to novel functions in mineral nutrition and homeostasis control.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan.

ABSTRACT
The root cap has a fundamental role in sensing environmental cues as well as regulating root growth via altered meristem activity. Despite this well-established role in the control of developmental processes in roots, the root cap's function in nutrition remains obscure. Here, we uncover its role in phosphate nutrition by targeted cellular inactivation or phosphate transport complementation in Arabidopsis, using a transactivation strategy with an innovative high-resolution real-time (33)P imaging technique. Remarkably, the diminutive size of the root cap cells at the root-to-soil exchange surface accounts for a significant amount of the total seedling phosphate uptake (approximately 20%). This level of Pi absorption is sufficient for shoot biomass production (up to a 180% gain in soil), as well as repression of Pi starvation-induced genes. These results extend our understanding of this important tissue from its previously described roles in environmental perception to novel functions in mineral nutrition and homeostasis control.

No MeSH data available.


Related in: MedlinePlus

Colocalization of the plasma membrane marker FM4-64 and PHT1;4-mCherry in the phf1 Q0171>>PHF1 line.(A) Images of lateral root cap cells. For arrow, see (B). (B) Intensity profile of FM4-64 and mCherry fluorescence signals along the white arrow indicated in (A). (C) Images of a root epidermis cell. Yellow: FM4-64, red: mCherry. Scale bar: 5 µm.DOI:http://dx.doi.org/10.7554/eLife.14577.008
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fig2s1: Colocalization of the plasma membrane marker FM4-64 and PHT1;4-mCherry in the phf1 Q0171>>PHF1 line.(A) Images of lateral root cap cells. For arrow, see (B). (B) Intensity profile of FM4-64 and mCherry fluorescence signals along the white arrow indicated in (A). (C) Images of a root epidermis cell. Yellow: FM4-64, red: mCherry. Scale bar: 5 µm.DOI:http://dx.doi.org/10.7554/eLife.14577.008

Mentions: As stated above, the high redundancy of Pi transporters poses technical difficulties to investigating their roles in a selected tissue. We used a PHF1 mutant (phf1-1) to circumvent this obstacle, as this mutation strongly reduces PHT1 accumulation in the PM, resulting in a 70–80% reduction in Pi uptake (Bayle et al., 2011; Gonzalez et al., 2005). Consequently, the phf1-1 mutant exhibits phosphate starvation traits in Pi-rich medium, although its growth is only slightly reduced. This offers an appropriate genetic tool for targeted PHF1 complementation to restore Pi uptake in specific tissues. Using the same GAL4/UAS system described above, we back-crossed the GAL4 enhancer trap driving expression in the root cap (line Q0171) in a phf1-1 background. The specific complementation of the root cap was obtained by introducing the UAS-PHF1 construct, producing the phf1 Q0171>>PHF1 line. The proper targeting of Pi transporters to the PM in the root tip of resulting plants was confirmed by introducing the fluorescent marker mCherry fused to the PHT1;4 gene driven by the constitutive 35S promoter. This produced a strong fluorescent signal in the columella and lateral root cap, where the GFP marker driven by GAL4/UAS was also observed (Figure 2A). The proper targeting of the PHT1;4-mCherry fusion protein was validated by its colocalization with the PM-specific FM4-64 dye (Figure 2—figure supplement 1A,B). This confirms that an effective restoration of PHT1 targeting in the root cap PM has taken place in the phf1 Q0171>>PHF1 line (Figure 2—figure supplement 1A,C). A very low, diffuse fluorescence signal could also be detected in other tissues (Figure 2—figure supplement 1C), corresponding to a previously reported low level of ER-retained protein in the phf1-1 mutant (Gonzalez et al., 2005; Bayle et al., 2011). The root cap specificity of the phf1 Q0171>>PHF1 complementation therefore provides a unique opportunity to investigate the effect of localized Pi uptake in the root cap with physiological studies.10.7554/eLife.14577.007Figure 2.Root cap complementation of the phf1-1 mutant in the phf1 QO171>>PHF1 line.


A novel role for the root cap in phosphate uptake and homeostasis.

Kanno S, Arrighi JF, Chiarenza S, Bayle V, Berthomé R, Péret B, Javot H, Delannoy E, Marin E, Nakanishi TM, Thibaud MC, Nussaume L - Elife (2016)

Colocalization of the plasma membrane marker FM4-64 and PHT1;4-mCherry in the phf1 Q0171>>PHF1 line.(A) Images of lateral root cap cells. For arrow, see (B). (B) Intensity profile of FM4-64 and mCherry fluorescence signals along the white arrow indicated in (A). (C) Images of a root epidermis cell. Yellow: FM4-64, red: mCherry. Scale bar: 5 µm.DOI:http://dx.doi.org/10.7554/eLife.14577.008
© Copyright Policy
Related In: Results  -  Collection

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fig2s1: Colocalization of the plasma membrane marker FM4-64 and PHT1;4-mCherry in the phf1 Q0171>>PHF1 line.(A) Images of lateral root cap cells. For arrow, see (B). (B) Intensity profile of FM4-64 and mCherry fluorescence signals along the white arrow indicated in (A). (C) Images of a root epidermis cell. Yellow: FM4-64, red: mCherry. Scale bar: 5 µm.DOI:http://dx.doi.org/10.7554/eLife.14577.008
Mentions: As stated above, the high redundancy of Pi transporters poses technical difficulties to investigating their roles in a selected tissue. We used a PHF1 mutant (phf1-1) to circumvent this obstacle, as this mutation strongly reduces PHT1 accumulation in the PM, resulting in a 70–80% reduction in Pi uptake (Bayle et al., 2011; Gonzalez et al., 2005). Consequently, the phf1-1 mutant exhibits phosphate starvation traits in Pi-rich medium, although its growth is only slightly reduced. This offers an appropriate genetic tool for targeted PHF1 complementation to restore Pi uptake in specific tissues. Using the same GAL4/UAS system described above, we back-crossed the GAL4 enhancer trap driving expression in the root cap (line Q0171) in a phf1-1 background. The specific complementation of the root cap was obtained by introducing the UAS-PHF1 construct, producing the phf1 Q0171>>PHF1 line. The proper targeting of Pi transporters to the PM in the root tip of resulting plants was confirmed by introducing the fluorescent marker mCherry fused to the PHT1;4 gene driven by the constitutive 35S promoter. This produced a strong fluorescent signal in the columella and lateral root cap, where the GFP marker driven by GAL4/UAS was also observed (Figure 2A). The proper targeting of the PHT1;4-mCherry fusion protein was validated by its colocalization with the PM-specific FM4-64 dye (Figure 2—figure supplement 1A,B). This confirms that an effective restoration of PHT1 targeting in the root cap PM has taken place in the phf1 Q0171>>PHF1 line (Figure 2—figure supplement 1A,C). A very low, diffuse fluorescence signal could also be detected in other tissues (Figure 2—figure supplement 1C), corresponding to a previously reported low level of ER-retained protein in the phf1-1 mutant (Gonzalez et al., 2005; Bayle et al., 2011). The root cap specificity of the phf1 Q0171>>PHF1 complementation therefore provides a unique opportunity to investigate the effect of localized Pi uptake in the root cap with physiological studies.10.7554/eLife.14577.007Figure 2.Root cap complementation of the phf1-1 mutant in the phf1 QO171>>PHF1 line.

Bottom Line: Remarkably, the diminutive size of the root cap cells at the root-to-soil exchange surface accounts for a significant amount of the total seedling phosphate uptake (approximately 20%).This level of Pi absorption is sufficient for shoot biomass production (up to a 180% gain in soil), as well as repression of Pi starvation-induced genes.These results extend our understanding of this important tissue from its previously described roles in environmental perception to novel functions in mineral nutrition and homeostasis control.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo, Japan.

ABSTRACT
The root cap has a fundamental role in sensing environmental cues as well as regulating root growth via altered meristem activity. Despite this well-established role in the control of developmental processes in roots, the root cap's function in nutrition remains obscure. Here, we uncover its role in phosphate nutrition by targeted cellular inactivation or phosphate transport complementation in Arabidopsis, using a transactivation strategy with an innovative high-resolution real-time (33)P imaging technique. Remarkably, the diminutive size of the root cap cells at the root-to-soil exchange surface accounts for a significant amount of the total seedling phosphate uptake (approximately 20%). This level of Pi absorption is sufficient for shoot biomass production (up to a 180% gain in soil), as well as repression of Pi starvation-induced genes. These results extend our understanding of this important tissue from its previously described roles in environmental perception to novel functions in mineral nutrition and homeostasis control.

No MeSH data available.


Related in: MedlinePlus