The α-subunit of a heterotrimeric G-protein from tobacco, NtGPα1, functions in K+ channel regulation in mesophyll cells

Abstract

Heterotrimeric GTPases (G-proteins) are implicated in many cellular signalling processes. In plants, a function of a specific G-protein has only recently been characterized. A cDNA clone encoding a G-protein α-subunit was isolated from tobacco (Nicotiana tabacum L.). The deduced amino acid sequence of this α-subunit (NtGPα1) has 91% homology to GPα1 from Arabidopsis thaliana. Sequence comparisons with other plant G-proteins show these two α-subunits belong to the only class of plant G-proteins known to date. The NtGPα1 cDNA was placed under the control of the CaMV 35S promoter both in sense and anti-sense orientation. These constructs were stably transformed into tobacco plants. As shown by patch-clamp experiments, mesophyll protoplasts of transformed tobacco plants over-expressing NtGPα1 sense or antisense RNA exhibited enhanced plasmalemma K+ conductances compared to the wild type. By contrast, mesophyll protoplasts of transformed tobacco plants expressing the cholera toxin A1-subunit, a G-protein activator, exhibited a reduced plasmalemma K+ conductance. These results indicate for the first time a role of a specific G-protein in the regulation of K+ channels.