Received February 13, 2008
Accepted April 22, 2008
G
1 + G2 
G
. Heterotrimeric G protein G-deficient mutants do not recapitulate all phenotypes of G-deficient mutants
Yuri Trusov , Wei Zhang , Sarah M. Assmann , and Jose Ramon Botella *
Plant Genetic Engineering Laboratory, Department of Botany, School of Integrative Biology, The University of Queensland, Brisbane, Queensland 4072, Australia; Biology Department, Penn State University, University Park, PA, 16802-5301, USA
* Corresponding author; email: j.botella{at}uq.edu.au.
Heterotrimeric G proteins are signaling molecules ubiquitous among all eukaryotes. The Arabidopsis genome contains one G
(GPA1) , one G
( (AGB1) and two G
subunit genes (AGG1 and AGG2). G 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 have previously reported that G- 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 G- and G-deficient mutants, including the double mutant lacking both G subunits. While G-deficient mutants are hypersensitivie to ABA-inhibition of seed germination and are hyposensitive to ABA-inhibition of stomatal opening and guard-cell inward K+ currents, none of the available G-deficient mutants show any deviation from wild type in these responses, nor do they show the hypocotyl elongation and hook development defects that are characteristic of G-deficient mutants. In addition, striking discrepancies were observed in the aerial organs of G- versus G-deficient mutants. In fact, none of the distinctive traits observed in G-deficient mutants (such as reduced size of cotyledons, leaves, flowers and siliques), are present in any of the G single and double mutants. Despite the considerable amount of phenotypic overlap between G- and G-deficient mutants, confirming the tight relationship between G 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.
