PLANT K-SUBUNITS ASSEMBLE INDISCRIMINATELY( CHANNEL ALPHA)

In plants a large diversity of inwardly rectifying K+ channels (K-in c hannels) has been observed between tissues and species. However, only three different types of voltage-dependent plant K+ uptake channel sub families have been cloned so tar. they relate either to KAT1, AKT1, or AtKC1. To explore the mechanisms underlying the channel diversity, we investigated the assembly of plant inwardly rectifying alpha-subunits . cRNA encoding five different K+ channel alpha-subunits of the three subfamilies (KAT1, KST1, AKT1, SKT1, and AtKC1) which were isolated fr om different tissues, species, and plant families (Arabidopsis thalian a and Solanum tuberosum) was reciprocally co-injected into Xenopus ooc ytes. We identified plant K+ channels as multimers. Moreover, using K channel mutants expressing different sensitivities to voltage, Cs+, C a2+, and H+, we could prove heteromers on the basis of their altered v oltage and modulator susceptibility. We discovered that, in contrast t o animal K+ channel alpha-subunits, functional aggregates of plant K+, channel alpha-subunits assembled indiscriminately. Interestingly, AKT -type channels from A. thaliana and S. tuberosum, which as homomers we re electrically silent in oocytes after co-expression, mediated K+ cur rents. Our findings suggest that K+ channel diversity in plants result s from nonselective heteromerization of different alpha-subunits, and thus depends on the spatial segregation of individual alpha-subunit po ols and the degree of temporal overlap and kinetics of expression.