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Plant and Cell Physiology Advance Access originally published online on August 3, 2009
Plant and Cell Physiology 2009 50(9):1681-1694; doi:10.1093/pcp/pcp113
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Dissection of the Relationship Between RACK1 and Heterotrimeric G-Proteins in Arabidopsis

Jianjun Guo1, Shucai Wang1, Junbi Wang1,2, Wei-Dong Huang2, Jiansheng Liang3 and Jin-Gui Chen1,*

1Department of Botany, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
2College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, PR China
3College of Bioscience and Biotechnology, Yangzhou University, Yangzhou 225009, PR China

*Corresponding author: E-mail, jingui{at}interchange.ubc.ca; Fax, +1-604-822-6089.


  Abstract

Mammalian receptor for activated C kinase 1 (RACK1) is a versatile scaffold protein, playing regulatory roles in multiple signal transduction pathways. Moreover, RACK1 interacts with the heterotrimeric G-proteins (G-proteins) and regulates some specific functions of Gβ{gamma}. Although the protein sequences of both RACK1 and G-proteins are highly conserved in Arabidopsis, their relationship remains elusive. Here we provide genetic and biochemical evidence that Arabidopsis RACK1 and G-proteins may act through a mechanism that is distinct from their counterparts in mammals. Loss-of-function alleles of RACK1A (the most abundantly expressed RACK1 gene in Arabidopsis) do not appear to share morphological and developmental phenotypes with loss-of-function alleles of GPA1 (encoding the sole G{alpha} in Arabidopsis) or AGB1 (encoding the sole Gβ in Arabidopsis). The analysis of gpa1 rack1a and agb1 rack1a double mutants suggested that the effect of RACK1A on morphological and developmental traits may occur independently of the presence or absence of the G-protein subunits. Although both RACK1A and G-protein subunits are negative regulators of ABA responses in the ABA inhibition of early seedling development, an additive ABA hypersensitivity was observed in gpa1 rack1a and agb1 rack1a double mutants. Biochemical analysis suggested that unlike their counterparts in mammals, RACK1 may not physically interact with AGB1. Taken together, these findings revealed some fundamental differences in the relationship of RACK1 and G-proteins between Arabidopsis and mammals.

Keywords: ABA - AGB1 - Early seedling development - GPA1 - RACK1 - Seed germination

Abbreviations: AGB1, Arabidopsis heterotrimeric G-protein β subunit; AGG1, Arabidopsis heterotrimeric G-protein {gamma} subunit 1; AGG2, Arabidopsis heterotrimeric G-protein {gamma} subunit 2; 3-AT, 3-amino-1,2,4-triazole; Co-IP, co-immunoprecipitation; FOA, fluoro-orotic acid; G, ; {alpha}, Gβ and G{gamma}, heterotrimeric G-protein {alpha}, β and {gamma} subunit; GPA1, Arabidopsis heterotrimeric G-protein {alpha} subunit; G-protein, heterotrimeric GTP-binding protein; GUS, β-glucuronidase; HA, haemagglutinin; PVDF, polyvinylidene fluoride; RACK1, receptor for activated C kinase 1; RGS, regulator of G-protein signaling; RT–PCR, reverse transcription–PCR.

(Received July 6, 2009; Accepted July 27, 2009)
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