Journal Article

Function of the α Subunit of Rice Heterotrimeric G Protein in Brassinosteroid Signaling

Katsuyuki Oki, Noriko Inaba, Kanako Kitagawa, Shozo Fujioka, Hidemi Kitano, Yukiko Fujisawa, Hisaharu Kato and Yukimoto Iwasaki

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 50, issue 1, pages 161-172
Published in print January 2009 | ISSN: 0032-0781
Published online November 2008 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcn182
Function of the α Subunit of Rice Heterotrimeric G Protein in Brassinosteroid Signaling

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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The α subunit of plant heterotrimeric G proteins (Gα) plays pivotal roles in multiple aspects of development and responses to plant hormones. Recently, several lines of evidence have shown that Gα participates in brassinosteroid (BR) responses in Arabidopsis and rice plants. In this study, we conducted a comprehensive analysis of the roles of the rice Gα in the responses to BR using a defective mutant of the Gα gene, T65d1. Decreased sensitivity to 24-epi-brassinolide (24-epiBL) in the T65d1 mutant was observed in many processes examined, e.g. in the inhibition of root growth and the promotion of coleoptile elongation. The T65d1 mutant also showed similar phenotypes to those of BR-deficient mutants, such as the specifically shortened second internode and the constitutive photomorphogenic growth phenotype under dark conditions. However, a negative feedback effect by 24-epiBL on the expression of BR biosynthetic genes was observed in the T65d1 mutant, and the levels of BR intermediates did not fluctuate in this mutant. To determine the epistatic relationship between the T65d1 mutant and d61-7, a weak allele of a rice BR receptor mutant, the two mutants were crossed. The T65d1/d61-7 double mutant showed no epistasis in the elongation inhibition of the internodes, the internode elongation pattern, the leaf angle and the morphological abnormality of leaf, except for the vertical length of seed and the seed weight. Our results suggest that the rice Gα affects the BR signaling cascade but the Gα may not be a signaling molecule in BRI1-meditated perception/transduction.

Keywords: Brassinosteroid; Heterotrimeric G-protein α subunit; Rice (Oryza sativa); Rice brassinosteroid insensitive1 (OsBRI1)

Journal Article.  6396 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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