Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Published on December 22, 2006; 10.1104/pp.106.084103

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Received May 25, 2006
Accepted December 10, 2006

Ectopic Expression of ABA2/GIN1 in Arabidopsis Promotes Seed Dormancy and Stress Tolerance

Pei-Chi Lin , San-Gwang Hwang , Akira Endo , Masanori Okamoto , Tomokazu Koshiba , and Wan-Hsing Cheng *

Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan, R.O.C.; Department of Biological Science, Tokyo Metropolitan University, Hachioji-shi, Tokyo 192-0397, Japan

* Corresponding author; email: whcheng{at}gate.sinica.edu.tw.

Abscisic acid (ABA) is an important phytohormone that plays a critical role in seed development, dormancy, and stress tolerance. NCED (9-cis-epoxycarotenoid dioxygenase) is the key enzyme controlling ABA biosynthesis and stress tolerance. In this study, we investigated the effect of ectopic expression of another ABA biosynthesis gene, ABA2 (or GLUCOSE INSENSITIVE1, GIN1) encoding a short-chain dehydrogenase/reductase (SDR1) in Arabidopsis (Arabidopsis thaliana). We show that ABA2 overexpressing transgenic plants with elevated ABA levels exhibited seed germination delay and more tolerance to salinity than the wild type when grown on agar plates and/or in soil. However, the germination delay was abolished in transgenic plants showing ABA levels over 2-fold higher than that of wild type grown on 250 mM NaCl. The data suggest that there are distinct mechanisms underlying ABA-mediated inhibition of seed germination under diverse stress. The ABA-deficient mutant, aba2 with a shorter primary root, can be restored to normal root growth by exogenous application of ABA, whereas the transgenic plants overexpressing ABA2 showed normal root growth. The data reflect that the basal levels of ABA are essential for maintaining normal primary root elongation. Furthermore, analysis of ABA2 promoter activity with ABA2::GUS transgenic plants revealed that the promoter activity was enhanced by multiple prolonged stresses such as drought, salinity, cold, and flooding, but not by short-term stress treatments. Coincidently, the prolonged drought stress treatment led to the upregulation of ABA biosynthetic and sugar-related genes. Thus, the data support that ABA2 is a late expression gene and might have a fine-tuning function in mediating ABA biosynthesis through primary metabolic changes in response to stress.






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