Philippar Katrin, Büchsenschütz Kai, Edwards David, Löffler Julia, Lüthen Hartwig, Kranz Erhard, Edwards Keith J, Hedrich Rainer
Julius-von-Sachs-Institut, Lehrstuhl Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Julius-von-Sachs-Platz 2, D-97082, Wuerzburg, Germany.
Plant Mol Biol. 2006 Jul;61(4-5):757-68. doi: 10.1007/s11103-006-0047-2.
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.
玉米（Zea mays）胚芽鞘中钾离子吸收通道ZMK1的转录水平以及相应的蛋白质密度受植物激素生长素调控。ZMK1参与生长素调节的胚芽鞘伸长以及向重力性和向光性。为了明确ZMK1在这些基本过程中的作用，我们筛选了含有Mutator标签Zmk1基因的玉米植株。通过位点选择法，我们在Zmk1中鉴定出三个Mutator转座子插入的独立等位基因。zmk1 - m1::Mu1植株的特征是ZMK1内含子1中有一个Mu1转座子。然而，当我们分析这些纯合突变体生长中的胚芽鞘中Zmk1的转录丰度时，发现钾离子通道等位基因过表达。因此，钾离子通道转录本水平的升高导致了一种生长表型，正如更高效的钾离子吸收所预期的那样，钾离子吸收是膨压形成的一个关键因素。在玉米胚胎发育过程中追踪Zmk1的表达情况时，我们发现这个钾离子通道基因在整个胚胎发育过程中持续表达，并在后期上调。与在胚胎发育中起重要作用一致，Zmk1 - zmk1 - m2::Mu8和zmk1 - m3::MuA2的外显子2和内含子2突变导致了致死的、有缺陷的籽粒表型。因此，这些结果证明了生长素调节的钾离子通道基因ZMK1在胚芽鞘生长和胚胎发育中的核心作用。
