title: Golgi localized barley MTP8 proteins facilitate Mn transport.
abstract: Many metabolic processes in plants are regulated by manganese (Mn) but limited information is available on the molecular mechanisms controlling cellular Mn homeostasis. In this study, a yeast assay was used to isolate and characterize two genes, MTP8.1 and MTP8.2, which encode membrane-bound proteins belonging to the cation diffusion facilitator (CDF) family in the cereal species barley (Hordeum vulgare). Transient expression in onion epidermal cells showed that MTP8.1 and MTP8.2 proteins fused to the green fluorescent protein (GFP) are localized to Golgi. When heterologously expressed in yeast, MTP8.1 and MTP8.2 were found to be Mn transporters catalysing Mn efflux in a similar manner as the Golgi localized endogenous yeast protein Pmr1p. The level of MTP8.1 transcripts in barley roots increased with external Mn supply ranging from deficiency to toxicity, while MTP8.2 transcripts decreased under the same conditions, indicating non-overlapping functions for the two genes. In barley leaves, the expression of both MTP8 genes declined in response to toxic Mn additions to the roots suggesting a role in ensuring proper delivery of Mn to Golgi. Based on the above we suggest that barley MTP8 proteins are involved in Mn loading to the Golgi apparatus and play a role in Mn homeostasis by delivering Mn to Mn-dependent enzymes and/or by facilitating Mn efflux via secretory vesicles. This study highlights the importance of MTP transporters in Mn homeostasis and is the first report of Golgi localized Mn2+ transport proteins in a monocot plant species.
authors.affiliation: Plant and Soil Science Laboratory, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Pai
authors.initials: P
authors.lastname: Pedas
authors.affiliation: Plant and Soil Science Laboratory, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Michaela
authors.initials: M
authors.lastname: Schiller Stokholm
authors.affiliation: Plant and Soil Science Laboratory, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Josefine Nymark
authors.initials: JN
authors.lastname: Hegelund
authors.affiliation: Plant and Soil Science Laboratory, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Anne Hald
authors.initials: AH
authors.lastname: Ladegård
authors.affiliation: Plant and Soil Science Laboratory, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Jan Kofod
authors.initials: JK
authors.lastname: Schjoerring
authors.affiliation: Plant and Soil Science Laboratory, Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Søren
authors.initials: S
authors.lastname: Husted
mesh_terms: D000220:Adaptation, Biological; D001692:Biological Transport; D018506:Gene Expression Regulation, Plant; D006056:Golgi Apparatus / Q000378:metabolism*; D001467:Hordeum / Q000235:genetics / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism
chemical_list: D026901:Membrane Transport Proteins; D010940:Plant Proteins; D008345:Manganese