Plant and Cell Physiology Advance Access originally published online on November 26, 2008
Plant and Cell Physiology 2009 50(1):161-172; doi:10.1093/pcp/pcn182
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Function of the 
Subunit of Rice Heterotrimeric G Protein in Brassinosteroid Signaling
1Department of Bioscience, Fukui Prefectural University, 4-1-1 Matsuoka Kenjyojima, Eiheiji-cho, Yoshida-gun, Fukui, 910-1195 Japan
2RIKEN, Advanced Science Institute, Wako-shi, Saitama, 351-0198 Japan
3Bioscience and Biotechnology Center, Nagoya University, Chikusa, Nagoya, 464-8604 Japan
*Corresponding author: E-mail, iwasaki{at}fpu.ac.jp; Fax, +81-766-61-6015.
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Abstract |
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The 
subunit of plant heterotrimeric G proteins (G) plays pivotal roles in multiple aspects of development and responses to plant hormones. Recently, several lines of evidence have shown that G participates in brassinosteroid (BR) responses in Arabidopsis and rice plants. In this study, we conducted a comprehensive analysis of the roles of the rice G in the responses to BR using a defective mutant of the G 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 G affects the BR signaling cascade but the G may not be a signaling molecule in BRI1-meditated perception/transduction.
Keywords:
Brassinosteroid - Heterotrimeric G-protein subunit - Rice (Oryza sativa) - Rice brassinosteroid insensitive1 (OsBRI1)
Abbreviations:
BR, brassinosteroid; DMSO, dimethylsulf-oxide; 24-epiBL, 24-epi-brassinolide; G, G protein subunit; RT–PCR, reverse transcription–PCR; SE, standard error; WT, wild-type.
(Received October 1, 2008; Accepted November 24, 2008)
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