title: High boron-induced ubiquitination regulates vacuolar sorting of the BOR1 borate transporter in Arabidopsis thaliana.
abstract: Boron homeostasis is important for plants, as boron is essential but is toxic in excess. Under high boron conditions, the Arabidopsis thaliana borate transporter BOR1 is trafficked from the plasma membrane (PM) to the vacuole via the endocytic pathway for degradation to avoid excess boron transport. Here, we show that boron-induced ubiquitination is required for vacuolar sorting of BOR1. We found that a substitution of lysine 590 with alanine (K590A) in BOR1 blocked degradation. BOR1 was mono- or diubiquitinated within several minutes after applying a high concentration of boron, whereas the K590A mutant was not. The K590A mutation abolished vacuolar transport of BOR1 but did not apparently affect polar localization to the inner PM domains. Furthermore, brefeldin A and wortmannin treatment suggested that Lys-590 is required for BOR1 translocation from an early endosomal compartment to multivesicular bodies. Our results show that boron-induced ubiquitination of BOR1 is not required for endocytosis from the PM but is crucial for the sorting of internalized BOR1 to multivesicular bodies for subsequent degradation in vacuoles.
authors.affiliation: Biotechnology Research Center, University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Kasai
authors.forename: Junpei
authors.initials: J
authors.lastname: Takano
authors.forename: Kyoko
authors.initials: K
authors.lastname: Miwa
authors.forename: Atsushi
authors.initials: A
authors.lastname: Toyoda
authors.forename: Toru
authors.initials: T
authors.lastname: Fujiwara
mesh_terms: D019943:Amino Acid Substitution; D000730:Androstadienes / Q000494:pharmacology; D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001895:Boron / Q000378:metabolism / Q000494:pharmacology*; D020126:Brefeldin A / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D011992:Endosomes / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D054875:Ubiquitination / Q000187:drug effects* / Q000502:physiology; D014617:Vacuoles / Q000235:genetics / Q000378:metabolism*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D017920:Antiporters; D029681:Arabidopsis Proteins; C469216:BOR1 protein, Arabidopsis; D011500:Protein Synthesis Inhibitors; D020126:Brefeldin A; D001895:Boron; D000077191:Wortmannin