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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

The Arabidopsis Tetratricopeptide Repeat-Containing Protein TTL1 Is Required for Osmotic Stress Responses and Abscisic Acid Sensitivity^1,[W]

Departamento de Biología Molecular y Bioquímica Universidad de Málaga, 29010 Málaga, Spain (A.R., A.L.S., V.V., M.A.B.); and the Center for Plant Environmental Stress Physiology, Purdue University, West Lafayette, Indiana 47907–2010 (R.A.B., A.L.H., P.M.H.)

Mutations in the Arabidopsis (Arabidopsis thaliana) TETRATRICOPEPTIDE-REPEAT THIOREDOXIN-LIKE 1 (TTL1) cause reduced tolerance to NaCl and osmotic stress that is characterized by reduced root elongation, disorganization of the root meristem, and impaired osmotic responses during germination and seedling development. Expression analyses of genes involved in abscisic acid (ABA) biosynthesis and catabolism suggest that TTL1 is not involved in the regulation of ABA levels but is required for ABA-regulated responses. TTL1 regulates the transcript levels of several dehydration-responsive genes, such as the transcription factor DREB2A, and genes encoding dehydration response proteins, such as ERD1 (early response to dehydration 1), ERD3, and COR15a. The TTL1 gene encodes a novel plant protein with tetratricopeptide repeats and a region with homology to thioredoxin proteins. Based on homology searches, there are four TTL members in the Arabidopsis genome with similar intron-exon structure and conserved amino acid domains. Proteins containing tetratricopeptide repeat motifs act as scaffold-forming multiprotein complexes and are emerging as essential elements for plant hormonal responses (such as gibberellin responses and ethylene biosynthesis). In this report, we identify TTL1 as a positive regulator of ABA signaling during germination and seedling development under stress.

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: Miguel A. Botella (mabotella{at}uma.es).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.085191

^* Corresponding author; e-mail mabotella{at}uma.es; fax 34–952–13–42–67.

Received June 15, 2006; accepted September 15, 2006; published September 22, 2006.