The auxin-induced K+ channel gene Zmk1 in maize functions in coleoptile growth and is required for embryo development

Katrin Philippar, Kai Büchsenschütz, David Edwards, Julia Löffler, Hartwig Lüthen, Erhard Kranz, Keith J. Edwards, Rainer Hedrich

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16 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)757-768
Number of pages12
JournalPlant Molecular Biology
Volume61
Issue number4-5
DOIs
Publication statusPublished - 1 Jan 2006
Externally publishedYes

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