Journal
PHYTOCHEMISTRY
Volume 68, Issue 11, Pages 1537-1544Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.phytochem.2007.03.041
Keywords
black cottonwood; poplar; Populus trichocarpa; salicaceae; methyltransferase; SABATH; indole-3-acetic acid; IAMT
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Indole-3-acetic acid (IAA) is the most active endogenous auxin and is involved in various physiological processes in higher plants. Concentrations of IAA in plant tissues are regulated at multiple levels including de novo biosynthesis, conjugation/deconjugation, and degradation. In this paper, we report molecular isolation and biochemical characterization of a gene PtIAMT1 from poplar encoding 1AA methyltransferase (IAMT), which plays a role in regulating IAA homeostasis. PtIAMT1 was identified from the poplar genome based on sequence similarity to Arabidopsis IAMT. A full-length cDNA of PtIAMT1 was cloned from poplar roots via RT-PCR. Recombinant PtIAMT1 expressed in Escherichia coli was purified to electrophoretic homogeneity. Enzyme assays combined with GC-MS verified that PtIAMT1 catalyzes formation of methyl indole-3-acetate using S-adenosyl-L-methionine (SAM) as a methyl donor and IAA as a methyl acceptor. PtIAMT1 had a temperature optimum at 25 degrees C and a pH optimum at pH 7.5. Its activity was promoted by K+ but inhibited by Fe2+, CU2+ and Zn2+. Under steady-state conditions, PtIAMT1 exhibited apparent K-m values of 23.1 mu M and 30.4 mu M for IAA and SAM, respectively. Gene expression analysis showed that PtIAMT1 had the highest level of expression in stems, a moderate level of expression in young leaves, and a low level of expression in roots. Presence of PtIAMT1 transcripts in several organs suggests that PtIAMT1 is involved in development of multiple organs in poplar. (c) 2007 Elsevier Ltd. All rights reserved.
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