The phytohormone auxin promotes cell expansion, division, and differentiation, thereby regulating a plethora of developmental events and environmental responses.  We have used Arabidopsis mutants to identify genes providing inputs to the auxin pool, to distinguish precursors from active auxin, and to disentangle contributions of different auxin biosynthetic pathways to development. 

We identified the enzymes that release auxin from precursors, discovered that the ER and peroxisomes compartmentalize auxin production pathways, and revealed the importance of different auxin sources for lateral root development, cotyledon expansion, root hair lengthening, and hypocotyl elongation.  Moreover, we discovered new classes of regulators of auxin precursor utilization, including components that modulate subcellular metal environments and a transporter family that displays a unique polar localization to the outer face of epidermal cells and effluxes an auxin precursor from roots. 

We isolated novel auxin-signaling mutants (ecr1, defective in a RUB-activating enzyme; iaa28 and iaa16, dominant alleles of Aux/IAA transcriptional repressors; and ibr5, defective in a MAP-kinase phosphatase) and exploited these mutants to illuminate the interactions of auxin signaling with other phytohormone pathways and novel facets of auxin signaling.  For example, we found that the ibr5 mutant displays multiple phenotypes suggesting that it responds less than wild type to both exogenous and endogenous auxin.  ibr5 also is less responsive than wild type to abscisic acid and ethylene. Unlike other auxin-response mutants, ibr5 impedes auxin responsiveness without stabilizing Aux/IAA repressors, like IAA28, indicating that IBR5 defines a new regulatory step acting downstream of previously identified auxin signaling modulators.

Our auxin signaling publications
Our auxin review articles