Auxin metabolism - Metabolic regulation of the plant hormone indole-3-acetic acid

NSF MCB-0725149 Collaborative Research: 2010 Arabidopsis: Cellular and Subcellular Resolution of the Tryptophan-Related Pathways 

The phytohormone indole-3-acetic acid (IAA, auxin) is important for many aspects of plant growth, development and responses to the environment yet the routes to is biosynthesis and mechanisms for regulation of IAA levels remain important research questions.  A critical issue concerning the biosynthesis if IAA in plants is that redundant pathways for IAA biosynthesis exist in plants.  We have shown that these redundant pathways and their relative contribution to net IAA production are under both developmental and environmental control.  We are working on three fundamental problems related to how plants get their IAA:

  1. An in vitro biochemical approach is being used to define the tryptophan dependent pathway to IAA using maize endosperm, where relatively large amounts of IAA are produced over a short developmental period.  Both a stable isotope dilution and a protein MS approach are being used to identify intermediates and enzymes in the reactions.
  2. We have developed an in vitro system for analysis of tryptophan-independent IAA biosynthesis in maize seedlings and we are using a metabolite profiling approach to isolate intermediates in this reaction.
  3. Arabidopsis contains a small family of genes that encode potential indolepyruvate decarboxylase enzymes.  We are cloning these genes and studying plants that are mutant in these genes and that over-express each member in the family in terms of the level and route of IAA biosynthesis.  Together, we hope to develop a comprehensive picture of the pathways and regulatory components that are involved in IAA homeostasis in higher plants.