First published online March 16, 2006; 10.1104/pp.106.079475
Plant Physiology 141:97-107 (2006)
© 2006 American Society of Plant Biologists
DEVELOPMENT AND HORMONE ACTION
CYP707A1 and CYP707A2, Which Encode Abscisic Acid 8'-Hydroxylases, Are Indispensable for Proper Control of Seed Dormancy and Germination in Arabidopsis1
Masanori Okamoto,
Ayuko Kuwahara,
Mistunori Seo,
Tetsuo Kushiro2,
Tadao Asami,
Nobuhiro Hirai,
Yuji Kamiya,
Tomokazu Koshiba and
Eiji Nambara*
RIKEN Plant Science Center, Yokohama, Kanagawa 2300045, Japan (M.O., A.K., M.S., T. Kushiro, Y.K., E.N.); Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 1920397, Japan (M.O., T. Koshiba); RIKEN, Discovery Research Institute, Wako, Saitama 3510198, Japan (T.A.); and International Innovation Center, Kyoto University, Kyoto 6068501, Japan (N.H.)
Endogenous abscisic acid (ABA) levels are regulated by both biosynthesis and catabolism of the hormone. ABA 8'-hydroxylase is considered to be the key catabolic enzyme in many physiological processes. We have previously identified that four members of the Arabidopsis (Arabidopsis thaliana) CYP707A gene family (CYP707A1 to CYP707A4) encode ABA 8'-hydroxylases, and that the cyp707a2 mutants showed an increase in ABA levels in dry and imbibed seeds. In this study, we showed that the cyp707a1 mutant accumulated ABA to higher levels in dry seeds than the cyp707a2 mutant. Expression analysis showed that the CYP707A1 was expressed predominantly during mid-maturation and was down-regulated during late-maturation. Concomitantly, the CYP707A2 transcript levels increased from late-maturation to mature dry seed. Phenotypic analysis of single and double cyp707a mutants indicates that the CYP707A1 is important for reducing ABA levels during mid-maturation. On the other hand, CYP707A2 is responsible for the regulation of ABA levels from late-maturation to germination. Moreover, CYP707A1 and CYP707A3 were also shown to be involved in postgermination growth. Spatial expression analysis suggests that CYP707A1 was expressed predominantly in embryo during mid-maturation, whereas CYP707A2 expression was detected in both embryo and endosperm from late-maturation to germination. Our results demonstrate that each CYP707A gene plays a distinct role during seed development and postgermination growth.
1 This work was supported by the Japan Society for the Promotion of Science for Young Scientists (research fellowship to M.O.).
2 Present address: Faculty of Pharmaceutical Sciences, the University of Tokyo, Bunkyo-ku, Tokyo 1130033, Japan.
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Eiji Nambara (nambara{at}postman.riken.go.jp).
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.106.079475.
* Corresponding author; e-mail nambara{at}postman.riken.go.jp; fax 81455039665.
Received December 5, 2005;
returned for revision February 21, 2006;
accepted February 28, 2006.
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