title: Long distance movement of DIR1 and investigation of the role of DIR1-like during systemic acquired resistance in Arabidopsis.
abstract: DIR1 is a lipid transfer protein (LTP) postulated to complex with and/or chaperone a signal(s) to distant leaves during Systemic Acquired Resistance (SAR) in Arabidopsis. DIR1 was detected in phloem sap-enriched petiole exudates collected from wild-type leaves induced for SAR, suggesting that DIR1 gains access to the phloem for movement from the induced leaf. Occasionally the defective in induced resistance1 (dir1-1) mutant displayed a partially SAR-competent phenotype and a DIR1-sized band in protein gel blots was detected in dir1-1 exudates suggesting that a highly similar protein, DIR1-like (At5g48490), may contribute to SAR. Recombinant protein studies demonstrated that DIR1 polyclonal antibodies recognize DIR1 and DIR1-like. Homology modeling of DIR1-like using the DIR1-phospholipid crystal structure as template, provides clues as to why the dir1-1 mutant is rarely SAR-competent. The contribution of DIR1 and DIR1-like during SAR was examined using an Agrobacterium-mediated transient expression-SAR assay and an estrogen-inducible DIR1-EGFP/dir1-1 line. We provide evidence that upon SAR induction, DIR1 moves down the leaf petiole to distant leaves. Our data also suggests that DIR1-like displays a reduced capacity to move to distant leaves during SAR and this may explain why dir1-1 is occasionally SAR-competent.
authors.affiliation: Department of Biology, McMaster University Hamilton, ON, Canada ; Plant Biotechnology Institute Saskatoon, SK, Canada.
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Champigny
authors.forename: Marisa
authors.initials: M
authors.lastname: Isaacs
authors.forename: Philip
authors.initials: P
authors.lastname: Carella
authors.forename: Jennifer
authors.initials: J
authors.lastname: Faubert
authors.forename: Pierre R
authors.initials: PR
authors.lastname: Fobert
authors.forename: Robin K
authors.initials: RK
authors.lastname: Cameron
keywords: DIR1; DIR1-like; lipid transfer protein; long distance signaling; systemic acquired resistance