Plant and Cell Physiology Advance Access originally published online on December 24, 2008
Plant and Cell Physiology 2009 50(2):330-340; 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
1Growth Regulation Research Group, RIKEN Plant Science Center (PSC), 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, 230-0045 Japan
2Metabolic Function Research Group, RIKEN PSC, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, 230-0045 Japan
3Department of Cell and Systems Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario M5S 3B2, Canada
4The Centre for the Analysis of Genome Evolution and Function (CAGEF), University of Toronto, Toronto, Ontario M5S 3B2, Canada
*Corresponding author: E-mail, eiji.nambara{at}utoronto.ca; Fax, +1-416-978-5878.
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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 the 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 the strongest expression in imbibed seed. Induction of CHO1 expression was observed 4 h after seed imbibition and reached a maximum level at 24 h. Induction of 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 the 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: ABA - Arabidopsis - Double AP2 protein - Germination - Nitrate - Sugar
Abbreviations: ABRE, ABA-responsive element; ANT, AINTEGUMENTA; AP2, APETALA2; BAC, bacterial artificial chromosome; CE1, coupling element1; CHO1, CHOTTO1; GO, gene ontology; MatDB, MIPS Arabidopsis thaliana Database; PLT, PLETHORA; QRT–PCR, quantitative reverse transcription–PCR; TAIR, The Arabidopsis Information Resource; VP1, Viviparous1; WRI1, WRINKLED1.
5These authors contributed equally to this work.
6Present address: Laboratory of Plant Organ Development National Institute for Basic Biology Nishigonaka 38, Myodaiji, Okazaki 444-8585 Aichi, Japan
(Received November 3, 2008; Accepted December 15, 2008)
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