The alpha-subunit of a heterotrimeric G-protein from tobacco, NtGP alpha 1, functions in K+ channel regulation in mesophyll cells

Heterotrimeric GTPases (G-proteins) are implicated in many cellular signall ing processes. In plants, a function of a specific G-protein has only recen tly been characterized. A cDNA clone encoding a G-protein alpha-subunit was isolated from tobacco (Nicotiana tabacum L.), The deduced amino acid seque nce of this alpha-subunit (NtGP alpha 1) has 91% homology to GP alpha 1 fro m Arabidopsis thaliana, Sequence comparisons with other plant G-proteins sh ow that these two a-subunits belong to the only class of plant G-proteins k nown to date. The NtGP alpha 1 cDNA was placed under the control of the CaM V 35S promoter both in sense and antisense orientation. These constructs we re stably transformed into tobacco plants. As shown by patch-clamp experime nts, mesophyll protoplasts of transformed tobacco plants over-expressing Nt GP alpha 1 sense or antisense RNA exhibited enhanced plasmalemma K+ conduct ances compared to the wild type. By contrast, mesophyll protoplasts of tran sformed tobacco plants expressing the cholera toxin A1-subunit, a G-protein activator, exhibited a reduced plasmalemma K+ conductance. These results i ndicate for the first time a role of a specific G-protein in the regulation of K+ channels.