Auxin activates KAT1 and KAT2, two K+-channel genes expressed in seedlings of Arabidopsis thaliana.
The transcript abundance of the K+-channel gene ZMK1 (Zea mays K+ channel 1) in maize coleoptiles is controlled by the phytohormone auxin. Thus, ZMK1 is thought to function in auxin-regulated coleoptile elongation, as well as during gravitropism and phototropism. To investigate related growth phenomena in the dicotyledonous plant Arabidopsis thaliana, we screened etiolated seedlings for auxin-induced K+-channel genes. Among the members of the Shaker-like K+ channels, we thereby identified transcripts of the inward rectifiers, KAT1 (K+ transporter of Arabidopsis thaliana) and KAT2, to be upregulated by auxin. The phloem-associated KAT2 was localised in cotyledons and the apical part of etiolated seedlings. In contrast, the K+-channel gene KAT1 was expressed in the cortex and epidermis of etiolated hypocotyls, as well as in flower stalks. Furthermore, KAT1 was induced by active auxins in auxin-sensitive tissues characterised by rapid cell elongation. Applying the patch-clamp technique to protoplasts of etiolated hypocotyls, we correlated the electrical properties of K+ currents with the expression profile of K+-channel genes. In KAT1-knockout mutants, K+ currents after auxin stimulation were characterised by reduced amplitudes. Thus, this change in the electrical properties of the K+-uptake channel in hypocotyl protoplasts resulted from an auxin-induced increase of active KAT1 proteins. The loss of KAT1-channel subunits, however, did not affect the auxin-induced growth rate of hypocotyls, pointing to compensation by residual, constitutive K+ transporters. From gene expression and electrophysiological data, we suggest that auxin regulation of KAT1 is involved in elongation growth of Arabidopsis. Furthermore, a role for KAT2 in the auxin-controlled vascular patterning of leaves is discussed.
Philippar
Katrin
K
Julius-von-Sachs-Institut, Lehrstuhl Molekulare Pflanzenphysiologie und Biophysik, Universität Würzburg, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany.
Ivashikina
Natalya
N
Ache
Peter
P
Christian
May
M
Lüthen
Hartwig
H
Palme
Klaus
K
Hedrich
Rainer
R
D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics*; D004594:Electrophysiology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018390:Gene Targeting; D017343:Genes, Plant / Q000187:drug effects*; D018546:Hypocotyl / Q000187:drug effects / Q000378:metabolism; D007210:Indoleacetic Acids / Q000494:pharmacology*; D009154:Mutation; D010940:Plant Proteins; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics*; D024661:Potassium Channels, Inwardly Rectifying; D024642:Potassium Channels, Voltage-Gated; D021122:Protein Subunits; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects / Q000378:metabolism
D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; C501210:KAT1 protein, Arabidopsis; C428126:KAT2 protein, Arabidopsis; D010940:Plant Proteins; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D024642:Potassium Channels, Voltage-Gated; D021122:Protein Subunits; D012333:RNA, Messenger; D018749:RNA, Plant