title: The auxin-induced K(+) channel gene Zmk1 in maize functions in coleoptile growth and is required for embryo development.
abstract: The transcript level and in turn protein density of the K(+)-uptake channel ZMK1 in maize (Zea mays) coleoptiles is controlled by the phytohormone auxin. ZMK1 is involved in auxin-regulated coleoptile elongation as well as gravi- and phototropism. To provide unequivocal evidence for the role of ZMK1 in these elementary processes we screened for maize plants containing a Mutator-tagged Zmk1 gene. In a site-selected approach, we were able to identify three independent alleles of Mutator-transposon insertions in Zmk1. zmk1-m1::Mu1 plants were characterised by a Mu1 transposon inside intron 1 of ZMK1. When we analysed the Zmk1-transcript abundance in growing coleoptiles of these homozygous mutants, however, we found the K(+)-channel allele overexpressed. In consequence, elevated levels of K(+)-channel transcripts resulted in a growth phenotype as expected from more efficient K(+)-uptake, representing a central factor for turgor formation. Following Zmk1 expression during maize embryogenesis, we found this K(+)-channel gene constitutively expressed throughout embryo development and upregulated in late stages. In line with a vital role in embryogenesis, the mutations of exon 2 and intron 2 of Zmk1-zmk1-m2::Mu8 and zmk1-m3::MuA2-caused a lethal, defective-kernel phenotype. Thus, these results demonstrate the central role of the auxin-regulated K(+)-channel gene Zmk1 in coleoptile growth and embryo development.
authors.affiliation: Julius-von-Sachs-Institut, Lehrstuhl Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Julius-von-Sachs-Platz 2, D-97082, Wuerzburg, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Philippar
authors.forename: Kai
authors.initials: K
authors.lastname: Büchsenschütz
authors.forename: David
authors.initials: D
authors.lastname: Edwards
authors.forename: Julia
authors.initials: J
authors.lastname: Löffler
authors.forename: Hartwig
authors.initials: H
authors.lastname: Lüthen
authors.forename: Erhard
authors.initials: E
authors.lastname: Kranz
authors.forename: Keith J
authors.initials: KJ
authors.lastname: Edwards
authors.forename: Rainer
authors.initials: R
authors.lastname: Hedrich
mesh_terms: D000483:Alleles; D018548:Cotyledon / Q000254:growth & development*; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D007210:Indoleacetic Acids / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D012639:Seeds / Q000378:metabolism*; D003313:Zea mays / Q000187:drug effects / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*
chemical_list: D007210:Indoleacetic Acids; D010940:Plant Proteins; D015221:Potassium Channels; C417562:ZMK1 protein, Zea mays