Mutant Allele-Specific Uncoupling of PENETRATION3 Functions Reveals Engagement of the ATP-Binding Cassette Transporter in Distinct Tryptophan Metabolic Pathways

Plant Physiol. 2015 Jul;168(3):814-27. doi: 10.1104/pp.15.00182. Epub 2015 May 28.


Arabidopsis (Arabidopsis thaliana) penetration (PEN) genes quantitatively contribute to the execution of different forms of plant immunity upon challenge with diverse leaf pathogens. PEN3 encodes a plasma membrane-resident pleiotropic drug resistance-type ATP-binding cassette transporter and is thought to act in a pathogen-inducible and PEN2 myrosinase-dependent metabolic pathway in extracellular defense. This metabolic pathway directs the intracellular biosynthesis and activation of tryptophan-derived indole glucosinolates for subsequent PEN3-mediated efflux across the plasma membrane at pathogen contact sites. However, PEN3 also functions in abiotic stress responses to cadmium and indole-3-butyric acid (IBA)-mediated auxin homeostasis in roots, raising the possibility that PEN3 exports multiple functionally unrelated substrates. Here, we describe the isolation of a pen3 allele, designated pen3-5, that encodes a dysfunctional protein that accumulates in planta like wild-type PEN3. The specific mutation in pen3-5 uncouples PEN3 functions in IBA-stimulated root growth modulation, callose deposition induced with a conserved peptide epitope of bacterial flagellin (flg22), and pathogen-inducible salicylic acid accumulation from PEN3 activity in extracellular defense, indicating the engagement of multiple PEN3 substrates in different PEN3-dependent biological processes. We identified 4-O-β-D-glucosyl-indol-3-yl formamide (4OGlcI3F) as a pathogen-inducible, tryptophan-derived compound that overaccumulates in pen3 leaf tissue and has biosynthesis that is dependent on an intact PEN2 metabolic pathway. We propose that a precursor of 4OGlcI3F is the PEN3 substrate in extracellular pathogen defense. These precursors, the shared indole core present in IBA and 4OGlcI3F, and allele-specific uncoupling of a subset of PEN3 functions suggest that PEN3 transports distinct indole-type metabolites in distinct biological processes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / chemistry
  • ATP-Binding Cassette Transporters / genetics*
  • ATP-Binding Cassette Transporters / metabolism
  • Adaptation, Physiological / drug effects
  • Alleles*
  • Amino Acid Sequence
  • Amino Acid Substitution
  • Arabidopsis / drug effects
  • Arabidopsis / metabolism*
  • Arabidopsis / microbiology
  • Ascomycota / physiology
  • Disease Susceptibility
  • Indoles / pharmacology
  • Metabolic Networks and Pathways* / drug effects
  • Models, Biological
  • Molecular Sequence Data
  • Mutation / genetics*
  • Pathogen-Associated Molecular Pattern Molecules / metabolism
  • Plant Diseases / microbiology
  • Plant Roots / drug effects
  • Plant Roots / growth & development
  • Salicylic Acid / metabolism
  • Tryptophan / metabolism*


  • ATP-Binding Cassette Transporters
  • Indoles
  • PDR8 protein, Arabidopsis
  • Pathogen-Associated Molecular Pattern Molecules
  • indolebutyric acid
  • Tryptophan
  • Salicylic Acid