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DEVELOPMENT AND HORMONE ACTION

Abscisic Acid and Gibberellin Differentially Regulate Expression of Genes of the SNF1-Related Kinase Complex in Tomato Seeds¹

Department of Vegetable Crops, One Shields Avenue, University of California, Davis, California 95616–8631

The SNF1/AMP-activated protein kinase subfamily plays central roles in metabolic and transcriptional responses to nutritional or environmental stresses. In yeast (Saccharomyces cerevisiae) and mammals, activating and anchoring subunits associate with and regulate the activity, substrate specificity, and cellular localization of the kinase subunit in response to changing nutrient sources or energy demands, and homologous SNF1-related kinase (SnRK1) proteins are present in plants. We isolated cDNAs corresponding to the kinase (LeSNF1), regulatory (LeSNF4), and localization (LeSIP1 and LeGAL83) subunits of the SnRK1 complex from tomato (Lycopersicon esculentum Mill.). LeSNF1 and LeSNF4 complemented yeast snf1 and snf4 mutants and physically interacted with each other and with LeSIP1 in a glucose-dependent manner in yeast two-hybrid assays. LeSNF4 mRNA became abundant at maximum dry weight accumulation during seed development and remained high when radicle protrusion was blocked by abscisic acid (ABA), water stress, far-red light, or dormancy, but was low or undetected in seeds that had completed germination or in gibberellin (GA)-deficient seeds stimulated to germinate by GA. In leaves, LeSNF4 was induced in response to ABA or dehydration. In contrast, LeSNF1 and LeGAL83 genes were essentially constitutively expressed in both seeds and leaves regardless of the developmental, hormonal, or environmental conditions. Regulation of LeSNF4 expression by ABA and GA provides a potential link between hormonal and sugar-sensing pathways controlling seed development, dormancy, and germination.

¹ This work was supported in part by the National Science Foundation (grant nos. IBN–9407264 and IBN–9722978) and by the U.S. Department of Agriculture-National Research Initiative Competitive Grants Program (grant no. 2001–35304 to K.J.B.).

³ Present address: Department of Horticulture, N322–C Agricultural Science Center North, University of Kentucky, Lexington, KY 40546–0091.

² Deceased.

⁴ Present address: Department of Biology, BSBE 201, Texas A&M University, College Station, TX 77843–3258.

⁵ Present address: 945 Lucena Court, Davis, CA 95616.

^* Corresponding author; e-mail kjbradford{at}ucdavis.edu; fax 530–752–4554.

Received December 15, 2002; returned for revision January 20, 2003; accepted March 12, 2003.

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