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Plant and Cell Physiology Advance Access originally published online on May 22, 2008
Plant and Cell Physiology 2008 49(7):1013-1024; doi:10.1093/pcp/pcn078
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© The Author 2008. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Loss-of-Function Mutations in the Arabidopsis Heterotrimeric G-protein {alpha} Subunit Enhance the Developmental Defects of Brassinosteroid Signaling and Biosynthesis Mutants

Yajun Gao1,2, Shucai Wang1, Tadao Asami3 and Jin-Gui Chen1,*

1 Department of Botany, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
2 College of Resources and Environment, Northwest Agriculture and Forestry University, Yangling, Shaanxi 712100, PR China
3 Plant Science Center and Plant Functions Laboratory, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama, 351-0198 Japan

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


  Abstract

Loss-of-function alleles of the sole heterotrimeric G-protein {alpha} subunit in Arabidopsis, GPA1, display defects in cell proliferation throughout plant development. Previous studies indicated that GPA1 is involved in brassinosteroid (BR) response. Here we provide genetic evidence that loss-of-function mutations in GPA1, gpa1-2 and gpa1-4, enhance the developmental defects of bri1-5, a weak allele of a BR receptor mutant, and det2-1, a BR-deficient mutant in Arabidopsis. gpa1-2 bri1-5 and gpa1-4 det2-1 double mutants had shorter hypocotyls, shorter roots and fewer lateral roots, and displayed more severe dwarfism than bri1-5 and det2-1 single mutants, respectively. By using the Arabidopsis hypocotyl as a model system where the parameters of cell division and cell elongation can be simultaneously measured, we found that gpa1 can specifically enhance the cell division defects of bri1-5 and det2-1 mutants. Similarly, gpa1 specifically enhances cell division defects in the primary roots of bri1-5 and det2-1 mutants. Furthermore, an additive effect on cell division between gpa1 and bri1-5 or det2-1 mutations was observed in the hypocotyls, whereas a synergistic effect was observed in the roots. Taken together, these results provided the first genetic evidence that G-protein- and BR-mediated pathways may be converged to modulate cell proliferation in a cell/tissue-specific manner.

Keywords: Arabidopsis - Brassinosteroid (BR) - Cell proliferation - Heterotrimeric G-protein {alpha} subunit (GPA1) - Hypocotyl - Root

Abbreviations: BR, brassinosteroid; GPA1, Arabidopsis heterotrimeric G-protein {alpha} subunit; GPCR, G-protein-coupled receptor; G-proteins, heterotrimeric guanine nucleotide-binding proteins.

(Received May 7, 2008; Accepted May 19, 2008)
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