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Muro K, Kamiyo J, Wang S, Geldner N, Takano J. Casparian strips prevent apoplastic diffusion of boric acid into root steles for excess B tolerance. FRONTIERS IN PLANT SCIENCE 2023; 14:988419. [PMID: 38162298 PMCID: PMC10755862 DOI: 10.3389/fpls.2023.988419] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Accepted: 12/01/2023] [Indexed: 01/03/2024]
Abstract
Casparian strips are ring-like structures consisting of lignin, sealing the apoplastic space between endodermal cells. They are thought to have important functions in controlling radial transport of nutrients and toxic elements in roots. However, Arabidopsis mutants with a defective Casparian strip structure have been found to maintain nutrient homeostasis in ranges supportive of growth under standard laboratory conditions. In this study, we investigated the function of Casparian strips under excess boron (B) conditions using sgn3 and sgn4 mutants with defective Casparian strip development but which do not exhibit excessive deposition of suberin, another endodermal diffusion barrier. The growth of sgn3 and sgn4 mutants did not differ significantly from that of wild-type (WT) plants under different B conditions in plate cultures; however, they were highly sensitive to B excess in hydroponic culture, where transpiration drives the translocation of boric acid toward the shoot. In hydroponic culture with sufficient to excess boric acid, B accumulation in shoots of the sgn3 and sgn4 mutants was higher than that in the WT. A time-course tracer study using 10B-enriched boric acid at a sufficient or slightly excessive concentration showed higher translocation of B into shoots of the sgn3 and sgn4 mutants. Furthermore, a genetically encoded biosensor for boric acid expressed under a stele-specific promoter (proCIF2:NIP5;1 5'UTR : Eluc-PEST) visualized faster boric acid flux into the mutant steles. Collectively, our results demonstrate the importance of Casparian strips in preventing apoplastic diffusion of boric acid into the stele under excess supply.
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Affiliation(s)
- Keita Muro
- Department of Agricultural Biology, Graduate School of Agriculture, Osaka Metropolitan University, Sakai, Japan
| | - Jio Kamiyo
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Japan
| | - Sheliang Wang
- Department Of Soil Science and Plant Nutrition, College of Resources and Environment, Huazhong Agricultural University, Wuhan, China
| | - Niko Geldner
- Department of Plant Molecular Biology, University of Lausanne, Lausanne, Switzerland
| | - Junpei Takano
- Department of Agricultural Biology, Graduate School of Agriculture, Osaka Metropolitan University, Sakai, Japan
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Yoshinari A, Hosokawa T, Beier MP, Oshima K, Ogino Y, Hori C, Takasuka TE, Fukao Y, Fujiwara T, Takano J. Transport-coupled ubiquitination of the borate transporter BOR1 for its boron-dependent degradation. THE PLANT CELL 2021; 33:420-438. [PMID: 33866370 PMCID: PMC8136889 DOI: 10.1093/plcell/koaa020] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 11/20/2020] [Indexed: 05/17/2023]
Abstract
Plants take up and translocate nutrients through transporters. In Arabidopsis thaliana, the borate exporter BOR1 acts as a key transporter under boron (B) limitation in the soil. Upon sufficient-B supply, BOR1 undergoes ubiquitination and is transported to the vacuole for degradation, to avoid overaccumulation of B. However, the mechanisms underlying B-sensing and ubiquitination of BOR1 are unknown. In this study, we confirmed the lysine-590 residue in the C-terminal cytosolic region of BOR1 as the direct ubiquitination site and showed that BOR1 undergoes K63-linked polyubiquitination. A forward genetic screen identified that amino acid residues located in vicinity of the substrate-binding pocket of BOR1 are essential for the vacuolar sorting. BOR1 variants that lack B-transport activity showed a significant reduction of polyubiquitination and subsequent vacuolar sorting. Coexpression of wild-type (WT) and a transport-defective variant of BOR1 in the same cells showed degradation of the WT but not the variant upon sufficient-B supply. These findings suggest that polyubiquitination of BOR1 relies on its conformational transition during the transport cycle. We propose a model in which BOR1, as a B transceptor, directly senses the B concentration and promotes its own polyubiquitination and vacuolar sorting for quick and precise maintenance of B homeostasis.
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Affiliation(s)
- Akira Yoshinari
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, 599-8531, Japan
- Graduate School of Agriculture, Hokkaido University, Sapporo, 060-8589 Hokkaido, Japan
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, 464-8601 Japan
| | - Takuya Hosokawa
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, 599-8531, Japan
| | - Marcel Pascal Beier
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, 599-8531, Japan
- Graduate School of Agricultural and Life Sciences, the University of Tokyo, Tokyo 113-8657, Japan
| | - Keishi Oshima
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, 599-8531, Japan
| | - Yuka Ogino
- Graduate School of Agriculture, Hokkaido University, Sapporo, 060-8589 Hokkaido, Japan
| | - Chiaki Hori
- Graduate School of Agriculture, Hokkaido University, Sapporo, 060-8589 Hokkaido, Japan
| | - Taichi E Takasuka
- Graduate School of Agriculture, Hokkaido University, Sapporo, 060-8589 Hokkaido, Japan
| | - Yoichiro Fukao
- Plant Global Education Project, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, 630-0101, Japan
- Department of Bioinformatics, Ritsumeikan University, 1-1-1, Nodihigashi, Kusatsu, 525-8577, Japan
| | - Toru Fujiwara
- Graduate School of Agricultural and Life Sciences, the University of Tokyo, Tokyo 113-8657, Japan
| | - Junpei Takano
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, 599-8531, Japan
- Graduate School of Agriculture, Hokkaido University, Sapporo, 060-8589 Hokkaido, Japan
- Author for communication:
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Yoshinari A, Toda Y, Takano J. GNOM-dependent endocytosis maintains polar localisation of the borate exporter BOR1 in Arabidopsis. Biol Cell 2021; 113:264-269. [PMID: 33443774 DOI: 10.1111/boc.202000106] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Revised: 01/06/2021] [Accepted: 01/08/2021] [Indexed: 11/30/2022]
Abstract
BACKGROUND INFORMATION Plants use transporters polarly localised in the plasma membrane for the directional transport of nutrients. The boric acid/borate (B) exporter BOR1 is localised polarly in the inner lateral domain of the plasma membrane in various root cells for efficient translocation of B under B limitation. With a high B supply, BOR1 is ubiquitinated and transported to vacuoles for degradation. The polar localisation and vacuolar targeting of BOR1 are maintained by different endocytosis mechanisms. RESULTS We demonstrated that one of the most utilised inhibitors in endosomal recycling, brefeldin A (BFA), inhibits the polar localisation of BOR1. BFA inhibits a subset of guanine-nucleotide exchange factors (ARF-GEFs), regulators of vesicle formation. Using a transgenic line expressing BFA-resistant engineered GNOM, we identified GNOM as the key ARF-GEF in endocytosis and maintenance of the polar localisation of BOR1. CONCLUSIONS AND SIGNIFICANCE We found that BFA inhibits the polar localisation of BOR1 by inhibiting GNOM activity. Our results suggest that GNOM-dependent endocytosis contributes to the maintenance of the polar localisation of BOR1 under B limitation. We propose a model of BOR1 transcytosis initiated from GNOM-dependent endocytosis.
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Affiliation(s)
- Akira Yoshinari
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya, Aichi, 464-8601, Japan.,Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, 599-8531, Japan
| | - Yosuke Toda
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya, Aichi, 464-8601, Japan.,Japan Science and Technology Agency, Kawaguchi, Saitama, 332-0012, Japan.,Phytometrics Inc., Minami, Hamamatsu, Shizuoka, 435-0036, Japan
| | - Junpei Takano
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka, 599-8531, Japan
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