Discovery of a multigene family of aquaporin silicon transporters in the primitive plant Equisetum arvense

Authors

  • Caroline Grégoire,

    1. Département de Phytologie – Faculté des Sciences de l’Agriculture et de l’Alimentation, Centre de Recherche en Horticulture, Université Laval, Pavillon Paul-Comtois, Québec city, QC, G1V 0A6, Canada
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  • Wilfried Rémus-Borel,

    1. Département de Phytologie – Faculté des Sciences de l’Agriculture et de l’Alimentation, Centre de Recherche en Horticulture, Université Laval, Pavillon Paul-Comtois, Québec city, QC, G1V 0A6, Canada
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    • Present address: Institut National de la Recherche Agronomique, UMR Santé et Agroécologie du Vignoble, 71 Av Edouard Bourleaux, 33140 Villenave d'Ornon, France.

  • Julien Vivancos,

    1. Département de Phytologie – Faculté des Sciences de l’Agriculture et de l’Alimentation, Centre de Recherche en Horticulture, Université Laval, Pavillon Paul-Comtois, Québec city, QC, G1V 0A6, Canada
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  • Caroline Labbé,

    1. Département de Phytologie – Faculté des Sciences de l’Agriculture et de l’Alimentation, Centre de Recherche en Horticulture, Université Laval, Pavillon Paul-Comtois, Québec city, QC, G1V 0A6, Canada
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  • François Belzile,

    1. Département de Phytologie – Faculté des Sciences de l’Agriculture et de l’Alimentation, Université Laval, Pavillon Charles-Eugène-Marchand, Québec city, QC, G1V 0A6, Canada
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  • Richard R. Bélanger

    Corresponding author
    1. Département de Phytologie – Faculté des Sciences de l’Agriculture et de l’Alimentation, Centre de Recherche en Horticulture, Université Laval, Pavillon Paul-Comtois, Québec city, QC, G1V 0A6, Canada
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(e-mail richard.belanger@fsaa.ulaval.ca).

Summary

Plants benefit greatly from silicon (Si) absorption provided that they contain Si transporters. The latter have recently been identified in the roots of some higher plants known to accumulate high concentrations of Si, and all share a high level of sequence identity. In this study, we searched for transporters in the primitive vascular plant Equisetum arvense (horsetail), which is a valuable but neglected model plant for the study of Si absorption, as it has one of the highest Si concentrations in the plant kingdom. Our initial attempts to identify Si transporters based on sequence homology with transporters from higher plants proved unsuccessful, suggesting a divergent structure or property in horsetail transporters. Subsequently, through sequencing of the horsetail root transcriptome and a search using amino acid sequences conserved in plant aquaporins, we were able to identify a multigene family of aquaporin Si transporters. Comparison of known functional domains and phylogenetic analysis of sequences revealed that the horsetail proteins belong to a different group than higher-plant Si transporters. In particular, the newly identified proteins contain a STAR pore as opposed to the GSGR pore common to all previously identified Si transporters. In order to determine its functionality, the proteins were heterologously expressed in both Xenopus oocytes and Arabidopsis, and the results showed that the horsetail proteins are extremely efficient a transporting Si. These findings offer new insights into the elusive properties of Si and its absorption by plants.

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