An Inhibitor of Tryptophan-Dependent Biosynthesis of Indole-3-Acetic Acid Alters Seedling Development in Arabidopsis
Although polar transport and the TIR1-dependent signaling pathway of the plant hormone auxin/indole-3-acetic acid (IAA) are well characterized, understanding of the biosynthetic pathway(s) leading to the production of IAA is still limited. Genetic dissection of IAA biosynthetic pathways has been complicated by the metabolic redundancy caused by the apparent existence of several parallel biosynthetic routes leading to IAA production. Valuable complementary tools for genetic as well as biochemical analysis of auxin biosynthesis would be molecular inhibitors capable of acting in vivo on specific or general components of the pathway(s), which unfortunately have been lacking. Several indole derivatives have been previously identified to inhibit tryptophan-dependent IAA biosynthesis in an in vitro system from maize endosperm. We examined the effect of one of them, 6-fluoroindole, on seedling development of Arabidopsis thaliana and tested its ability to inhibit IAA biosynthesis in feeding experiments in vivo. We demonstrated a correlation of severe developmental defects or growth retardation caused by 6-fluoroindole with significant downregulation of de novo synthesized IAA levels, derived from the stable isotope-labeled tryptophan pool, upon treatment. Hence, 6-fluoroindole shows important features of an inhibitor of tryptophan-dependent IAA biosynthesis both in vitro and in vivo and thus may find use as a promising molecular tool for the identification of novel components of the auxin biosynthetic pathway(s).
KeywordsAuxin biosynthesis Inhibitor Arabidopsis thaliana Indole-3-acetic acid 6-Fluoroindole
We thank Silvia Heinze for technical assistance and Annett Kohlberg and Tilo Lübken for graphical assistance. This work was partially supported by a grant of the ‘Exzellenznetzwerk Biowissenschaften’ from the state Sachsen-Anhalt to MQ and by the U.S. National Science Foundation NSF2010 grant MCB0724970 and USDA-NRI grant 2005-35318-16197 to JDC. Furthermore, helpful suggestions of two anonymous reviewers are gratefully acknowledged.
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