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JXB Advance Access originally published online on April 2, 2009
Journal of Experimental Botany 2009 60(7):1991-2003; doi:10.1093/jxb/erp060
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

The {alpha}-subunit of the heterotrimeric G-protein affects jasmonate responses in Arabidopsis thaliana

Haruko Okamoto1,*, Cornelia Göbel2, Richard G. Capper3, Nigel Saunders3, Ivo Feussner2 and Marc R. Knight1,4

1Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK
2Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August University Göttingen, Justus-von-Liebig-Weg 11, D-37077 Göttingen, Germany
3Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK
4Department of Biological and Biomedical Sciences, Durham University, South Road, Durham DH1 3LE, UK

* To whom correspondence should be addressed. E-mail: haruko.okamoto{at}plants.ox.ac.uk

Heterotrimeric G-proteins have been implicated in having a role in many plant signalling pathways. To understand further the role of G-proteins, a preliminary experiment was performed to assess the impact of the G{alpha} subunit loss-of-function mutation gpa1-1 on the Arabidopsis transcriptome. The analysis indicated that the G{alpha} subunit may play a role in response to jasmonic acid (JA). Consistent with this, G{alpha} mutants showed a reduced response to JA in inhibition of chlorophyll accumulation and root growth, whilst G{alpha} gain-of-function plants overexpressing G{alpha} showed the opposite phenotype. The levels of JA and related compounds were unaffected in the gpa1-1 mutant, as was autoregulation of the Allene Oxide Synthase (AOS) gene that encodes a key enzyme for JA biosynthesis. In contrast, further analyses using G{alpha} loss- and gain-of-function Arabidopsis lines indicated that G{alpha} positively modulates the expression of the Vegetative Storage Protein (VSP) gene. This indicates that the G{alpha} subunit regulates a subset of JA-regulated genes defining a branch point in this signalling pathway in Arabidopsis. Further analysis of the impact of G{alpha} loss of function upon the JA-regulated transcriptome using Arabidopsis full genome arrays indicated that up to 29% of genes that are >2-fold regulated by JA in the wild type are misregulated in the G{alpha} mutant. This supports the observation that a significant proportion of, but not all, JA-regulated gene expression is mediated by G{alpha}.

Key words: AOS, Arabidopsis, heterotrimeric G-protein, G-protein {alpha}-subunit (GPA1), jasmonic acid, PDF1.2, VSP

Received 20 October 2008; Revised 29 December 2008 Accepted 30 January 2009


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