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DEVELOPMENT AND HORMONE ACTION

IAR4, a Gene Required for Auxin Conjugate Sensitivity in Arabidopsis, Encodes a Pyruvate Dehydrogenase E1 Homolog¹

Department of Biochemistry and Cell Biology, Rice University, Houston, Texas, 77005

The formation and hydrolysis of indole-3-acetic acid (IAA) conjugates represent a potentially important means for plants to regulate IAA levels and thereby auxin responses. The identification and characterization of mutants defective in these processes is advancing the understanding of auxin regulation and response. Here we report the isolation and characterization of the Arabidopsis iar4 mutant, which has reduced sensitivity to several IAA-amino acid conjugates. iar4 is less sensitive to a synthetic auxin and low concentrations of an ethylene precursor but responds to free IAA and other hormones tested similarly to wild type. The gene defective in iar4 encodes a homolog of the E1-subunit of mitochondrial pyruvate dehydrogenase, which converts pyruvate to acetyl-coenzyme A. We did not detect glycolysis or Krebs-cycle-related defects in the iar4 mutant, and a T-DNA insertion in the IAR4 coding sequence conferred similar phenotypes as the originally identified missense allele. In contrast, we found that disruption of the previously described mitochondrial pyruvate dehydrogenase E1-subunit does not alter IAA-Ala responsiveness or confer any obvious phenotypes. It is possible that IAR4 acts in the conversion of indole-3-pyruvate to indole-3-acetyl-coenzyme A, which is a potential precursor of IAA and IAA conjugates.

² Present address: Stoller Enterprises, 4001 W. Sam Houston Parkway N., Suite 100, Houston, TX 77043.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.040519.

^* Corresponding author; e-mail bartel{at}rice.edu; fax 713–348–5154.

Received February 4, 2004; returned for revision March 20, 2004; accepted March 21, 2004.

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