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Abstract

Kdc1 is a novel K+-channel gene cloned from carrot roots, and which is also present in cultured carrot cells. We investigated the characteristics of the ionic current elicited in Xenopus oocytes coinjected with KDC1 (K+-Daucus carota 1) and KAT1 (from Arabidopsis thaliana) RNA. Expressed heteromeric channels displayed inward-rectifying potassium currents whose kinetics, voltage characteristics, and inhibition by metal ions depended on KDC1:KAT1 ratios. At low KDC1:KAT1 ratios, Zn2+ inhibition of heteromeric K+ current was less pronounced compared to homomeric KAT1 channels, while at higher KDC1:KAT1 ratios, the addition of Zn2+ even produced an increase in current. Under the same conditions, the Ni2+ inhibition of the current was also reduced, but no current increase was observed. These effects might be explained by the unusual amino acid composition of the KDC1 protein in terms of histidine residues that are absent in the pore region, but abundant (four per subunit) in the proximity of the pore entrance. Channels like KDC1 could be at least partially responsible for the higher resistance of carrot cells in the presence of metals.

DKT1, a novel K+ channel from carrot, forms functional heteromeric channels with KDC1

“…This suggests the formation of heteromultimeric channels between KDC1 and DKT1 subunits. In line with the results obtained with KDC1, which forms heteromeric potassium channels with KAT1 [9], the ability of DKT1 to form heteromultimeric channels with KAT1 was also verified by the co‐expression in Xenopus oocytes. The DKT1:KAT1 channel displayed large inward rectifying currents with modified characteristics with respect to homomeric KAT1 (data not shown).…”

“…The results presented on DKT1 localization together with the whole mount and in situ hybridisation experiments reported for KDC1, the first potassium channel isolated from carrot [7,24], demonstrate that the channels are co‐localised in many plant tissues, in roots (endodermis, epidermis and hairs), SAM and embryo cotyledons (summed up in Table 1 ), therefore suggesting a possible interaction between the two channels. It has been widely demonstrated that plant K + channels can co‐assemble [8–11,25], and we have previously shown that KDC1 can act as a modulator subunit when co‐expressed with KAT1 [9,10], we thus wanted to see if KDC1 can form functional heteromeric channels with DKT1. Interestingly, we obtained exceptionally robust and stable negative inwardly‐rectifying ionic currents in almost all oocytes which were co‐injected with KDC1 and DKT1.…”

“…A more detailed study was conducted in Xenopus oocytes where KDC1 does not form functional homomeric channels alone, however, when co‐injected with the Arabidopsis KAT1 α‐subunit, it forms heteromeric channels. KDC1:KAT1 heteromers show current activation which is significantly different from those of the homomeric KAT1 channel, demonstrating the modulator capability of KDC1 on other channels [9,10].…”

AtKC1, a silent Arabidopsis potassium channel α-subunit modulates root hair K + influx

“…Previous studies (25) have shown that AtKC1 seems not to form functional K ϩ channels when solely expressed in Xenopus oocytes, human embryo kidney 293 cells, or Sf9 insect cells (unpublished observations). Coexpression of AtKC1 or its orthologue KDC1 with members of other subfamilies strongly affected gating, kinetics, selectivity, and heavy metal resistance (25,30). Therefore, we studied the potassium conductance of AtKC1 expressing root hair protoplasts isolated from 7-day-old seedlings grown on filter paper.…”

“…Besides regulation of channel genes and proteins at the transcriptional (20) or at the posttranslational level (21), respectively, heteromeric assembly of different ␣-subunits might provide the molecular basis for the functional diversity observed in vivo (22)(23)(24). Although there is still controversy over them (25,26), biochemical and electrophysiological data suggest that, like animal potassium channels (27), different ␣-subunits of one channel family form heterooligomeric channels (18,25,(28)(29)(30).…”