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Plant Cell Physiol. 2016 Sep;57(9):1985-2000. doi: 10.1093/pcp/pcw121. Epub 2016 Jul 21.

DRP1-Dependent Endocytosis is Essential for Polar Localization and Boron-Induced Degradation of the Borate Transporter BOR1 in Arabidopsis thaliana.

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Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai, 599-8531 Japan Graduate School of Agriculture, Hokkaido University, Kita-9, Nishi-9, Kita-ku, Sapporo, 060-8589 Japan.
Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-8657 Japan.
National Institute for Basic Biology, Nishigonaka 38, Myodaiji, Okazaki, 444-8585 Japan Japan Science and Technology Agency (JST), PRESTO, Honcho 4-1-8, Kawaguchi, 332-0012 Japan.
Graduate School of Biological Sciences, Nara Institute of Sciences and Technology, Takayama 8916-5, Ikoma, Nara, 630-0192 Japan.
Research Faculty of Agriculture, Hokkaido University, Kita-10, Nishi-7, Kita-ku, Sapporo, 060-0810 Japan.
Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Gakuen-cho 1-1, Naka-ku, Sakai, 599-8531 Japan


Boron (B) is essential for plants but toxic in excess. The borate efflux transporter BOR1 is expressed in various root cells and localized to the inner/stele-side domain of the plasma membrane (PM) under low-B conditions. BOR1 is rapidly degraded through endocytosis upon sufficient B supply. The polar localization and degradation of BOR1 are considered important for efficient B translocation and avoidance of B toxicity, respectively. In this study, we first analyzed the subcellular localization of BOR1 in roots, cotyledons and hypocotyls, and revealed a polar localization in various cell types. We also found that the inner polarity of BOR1 is established after completion of cytokinesis in the root meristem. Moreover, variable-angle epifluorescence microscopy visualized BOR1-green fluorescent protein (GFP) as particles in the PM with significant lateral movements but in restricted areas. Importantly, a portion of BOR1-GFP particles co-localized with DYNAMIN-RELATED PROTEIN 1A (DRP1A), which is involved in scission of the clathrin-coated vesicles, and they disappeared together from the PM. To examine the contribution of DRP1A-mediated endocytosis to BOR1 localization and degradation, we developed an inducible expression system of the DRP1A K47A variant. The DRP1A variant prolonged the residence time of clathrin on the PM and inhibited endocytosis of membrane lipids. The dominant-negative DRP1A blocked endocytosis of BOR1 and disturbed its polar localization and B-induced degradation. Our results provided insight into the endocytic mechanisms that modulate the subcellular localization and abundance of a mineral transporter for nutrient homeostasis in plant cells.


Boron; Clathrin; Dynamin; Endocytosis; Polar localization; Transporter

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