Auxin activates KAT1 and KAT2, two K⁺‐channel genes expressed in seedlings of Arabidopsis thaliana

Abstract

SummaryThe 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 identi®ed transcripts of the inward recti®ers, 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¯ower 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 pro®le 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.

Mathematical model of morphogen electrophoresis through gap junctions

“…This kind of positive feedback amplification loop (Jaffe et al, 1974) parallels the feedback loop highlighted in Fukumoto et al (2005), due to the interaction between 5HT and K ϩ flow through 5HT-R3. Like serotonin (Hirdes et al, 2005), auxin also activates K ϩ channels (Philippar et al, 1999(Philippar et al, , 2004Fuchs et al, 2003). The many molecular and biophysical similarities between the auxin and serotonin pathways may represent a profound evolutionary conservation of patterning mechanisms, consistent with the conservation of fusicoccin signaling between plants, fungi, and vertebrate asymmetry (Bunney et al, 2003), or may reveal a convergence of mechanisms to achieve similar purposes from different molecular genetic starting points.…”

ArabidopsisTic62 and Ferredoxin-NADP(H) Oxidoreductase Form Light-Regulated Complexes That Are Integrated into the Chloroplast Redox Poise

“…The RNA was digested with DNase and reverse transcribed into cDNA. Detection and quantification of transcripts were performed as described previously (Philippar et al, 2004) using a LightCycler (Roche). For TIC62, we constructed the gene-specific primers Ex3fwd (59-CTG-GGATTTCGGGTTAGAG-39) and Ex7rev (59-CGTAATTAAGACCGCTTT-CA-39), amplifying a product of 416 bp, spanning both sites of the T-DNA insertion of tic62-1.…”

Osmotic Stress Responses and Plant Growth Controlled by Potassium Transporters inArabidopsis

“…Auxin is essential for plant growth and development, affecting cell expansion and division via the activation of ion fluxes, including K + , by factors such as the auxin binding protein ABP1 (Philippar et al, 2004;Braun et al, 2008;Tromas et al, 2010). We characterized the auxin sensitivities of the kup mutants in lateral root (LR) formation.…”