title: Transcriptome sequencing identifies SPL7-regulated copper acquisition genes FRO4/FRO5 and the copper dependence of iron homeostasis in Arabidopsis.
abstract: The transition metal copper (Cu) is essential for all living organisms but is toxic when present in excess. To identify Cu deficiency responses comprehensively, we conducted genome-wide sequencing-based transcript profiling of Arabidopsis thaliana wild-type plants and of a mutant defective in the gene encoding SQUAMOSA PROMOTER BINDING PROTEIN-LIKE7 (SPL7), which acts as a transcriptional regulator of Cu deficiency responses. In response to Cu deficiency, FERRIC REDUCTASE OXIDASE5 (FRO5) and FRO4 transcript levels increased strongly, in an SPL7-dependent manner. Biochemical assays and confocal imaging of a Cu-specific fluorophore showed that high-affinity root Cu uptake requires prior FRO5/FRO4-dependent Cu(II)-specific reduction to Cu(I) and SPL7 function. Plant iron (Fe) deficiency markers were activated in Cu-deficient media, in which reduced growth of the spl7 mutant was partially rescued by Fe supplementation. Cultivation in Cu-deficient media caused a defect in root-to-shoot Fe translocation, which was exacerbated in spl7 and associated with a lack of ferroxidase activity. This is consistent with a possible role for a multicopper oxidase in Arabidopsis Fe homeostasis, as previously described in yeast, humans, and green algae. These insights into root Cu uptake and the interaction between Cu and Fe homeostasis will advance plant nutrition, crop breeding, and biogeochemical research.
authors.affiliation: Department of Plant Physiology, Ruhr University Bochum, D-44801 Bochum, Germany.
authors.forename: María
authors.initials: M
authors.lastname: Bernal
authors.forename: David
authors.initials: D
authors.lastname: Casero
authors.forename: Vasantika
authors.initials: V
authors.lastname: Singh
authors.forename: Grandon T
authors.initials: GT
authors.lastname: Wilson
authors.forename: Arne
authors.initials: A
authors.lastname: Grande
authors.forename: Huijun
authors.initials: H
authors.lastname: Yang
authors.forename: Sheel C
authors.initials: SC
authors.lastname: Dodani
authors.forename: Matteo
authors.initials: M
authors.lastname: Pellegrini
authors.forename: Peter
authors.initials: P
authors.lastname: Huijser
authors.forename: Erin L
authors.initials: EL
authors.lastname: Connolly
authors.forename: Sabeeha S
authors.initials: SS
authors.lastname: Merchant
authors.forename: Ute
authors.initials: U
authors.lastname: Krämer
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003300:Copper / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D038181:FMN Reductase / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D055785:Gene Knockdown Techniques; D059014:High-Throughput Nucleotide Sequencing; D006706:Homeostasis; D007501:Iron / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D059467:Transcriptome
chemical_list: D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; D018749:RNA, Plant; C483288:SPL7 protein, Arabidopsis; D014157:Transcription Factors; D003300:Copper; D007501:Iron; D038181:FMN Reductase; C023903:ferric citrate iron reductase