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CELL BIOLOGY AND SIGNAL TRANSDUCTION

G1 + G2 Gβ: Heterotrimeric G Protein G-Deficient Mutants Do Not Recapitulate All Phenotypes of Gβ-Deficient Mutants^{1,[C],[W],[OA]}

Plant Genetic Engineering Laboratory, Department of Botany, School of Integrative Biology, University of Queensland, Brisbane, Queensland 4072, Australia (Y.T., J.R.B.); and Biology Department, Pennsylvania State University, University Park, Pennsylvania 16802–5301 (W.Z., S.M.A.)

Heterotrimeric G proteins are signaling molecules ubiquitous among all eukaryotes. The Arabidopsis (Arabidopsis thaliana) genome contains one G (GPA1), one Gβ (AGB1), and two G subunit (AGG1 and AGG2) genes. The Gβ requirement of a functional G subunit for active signaling predicts that a mutant lacking both AGG1 and AGG2 proteins should phenotypically resemble mutants lacking AGB1 in all respects. We previously reported that Gβ- and G-deficient mutants coincide during plant pathogen interaction, lateral root development, gravitropic response, and some aspects of seed germination. Here, we report a number of phenotypic discrepancies between Gβ- and G-deficient mutants, including the double mutant lacking both G subunits. While Gβ-deficient mutants are hypersensitive to abscisic acid inhibition of seed germination and are hyposensitive to abscisic acid inhibition of stomatal opening and guard cell inward K⁺ currents, none of the available G-deficient mutants shows any deviation from the wild type in these responses, nor do they show the hypocotyl elongation and hook development defects that are characteristic of Gβ-deficient mutants. In addition, striking discrepancies were observed in the aerial organs of Gβ- versus G-deficient mutants. In fact, none of the distinctive traits observed in Gβ-deficient mutants (such as reduced size of cotyledons, leaves, flowers, and siliques) is present in any of the G single and double mutants. Despite the considerable amount of phenotypic overlap between Gβ- and G-deficient mutants, confirming the tight relationship between Gβ and G subunits in plants, considering the significant differences reported here, we hypothesize the existence of new and as yet unknown elements in the heterotrimeric G protein signaling complex.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: José Ramón Botella (j.botella{at}uq.edu.au).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.117655

^* Corresponding author; e-mail j.botella{at}uq.edu.au.

Received February 13, 2008; accepted April 22, 2008; published April 25, 2008.

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