Plant and Cell Physiology Advance Access published online on December 24, 2008
Plant and Cell Physiology, doi:10.1093/pcp/pcn201
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CHOTTO1, a double AP2 domain protein of Arabidopsis thaliana, regulates germination and seedling growth under excess supply of glucose and nitrate
1 Growth Regulation Research Group, RIKEN Plant Science Center (PSC), 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045 Japan
2 Metabolic Function Research Group, RIKEN PSC, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045 Japan
3 Department of Cell and Systems Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario M5S3B2, Canada
4 The Centre for the Analysis of Genome Evolution and Function (CAGEF), University of Toronto, Toronto, Ontario M5S 3B2 Canada
5 These authors contributed equally to this work.
6 Correspondence should be addressed.
Corresponding author: Dr.Eiji Nambara, Department of Cell & Systems Biology University of Toronto 25 Willcocks Street, Toronto, Ontario M5S 3B2, Canada Tel; 1-416-978-4668 Fax; 1-416-978-5878 E-mail address: eiji.nambara{at}utoronto.ca
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Abstract |
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Arabidopsis chotto1 (cho1) mutants show resistance to (-)-R-ABA, an ABA analog, during germination and seedling growth. Here, we report cloning and characterization of the CHO1 gene. cho1 mutants showed only subtle resistance to (+)-S-ABA during germination. The cho1 mutation acts as a strong enhancer of the abi5 mutant, whereas cho1 abi4 double mutant showed ABA resistance similar to the abi4 single mutant. This suggests that CHO1 and ABI4, but not ABI5, act in the same genetic pathway. Map-based cloning revealed that the CHO1 gene encodes a putative transcription factor containing double AP2 domains. The CHO1 gene was expressed predominantly in seed, with strongest expression in imbibed seed. Induction of the CHO1 expression was observed 4 h after seed imbibition and reached a maximum level at 24 h. Induction of the CHO1 expression did not occur in the abi4 mutants, indicating that this is an ABI4-dependent process. Microarray experiments showed that a large number of genes involved in primary metabolism and stress response were up-regulated in the cho1 mutant. Growth of abi4 and cho1 mutant seedlings was resistant to high concentrations of glucose. In addition, growth of cho1 mutant seedlings was partially resistant to excess nitrate (50 mM), as evident from their expanded green cotyledons. However, their growth was normal under moderate nitrate concentrations (<10 mM). This nitrate response was specific to the cho1 mutants and was not observed in the abi4 mutants. Taken together, our results indicate that CHO1 regulates nutritional responses downstream of ABI4 during germination and seedling growth.
Keywords: abscisic acid - Arabidopsis - double AP2 protein - germination - nitrate - sugar
(Received November 3, 2008; Accepted December 15, 2008)
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