title: Detached and attached Arabidopsis leaf assays reveal distinctive defense responses against hemibiotrophic Colletotrichum spp.
abstract: The agriculturally important genus Colletotrichum is an emerging model pathogen for studying defense in Arabidopsis. During the process of screening for novel pathogenic Colletotrichum isolates on Arabidopsis, we found significant differences in defense responses between detached and attached leaf assays. A near-adapted isolate Colletotrichum linicola A1 could launch a typical infection only on detached, but not attached, Arabidopsis leaves. Remarkably, resistance gene-like locus RCH1-mediated resistance in intact plants also was compromised in detached leaves during the attacks with the virulent reference isolate C. higginsianum. The differences in symptom development between the detached leaf and intact plant assays were further confirmed on defense-defective mutants following inoculation with C. higginsianum, where the greatest inconsistency occurred on ethylene-insensitive mutants. In intact Arabidopsis plants, both the salicylic acid- and ethylene-dependent pathways were required for resistance to C. higginsianum and were associated with induced expression of pathogenesis-related genes PR1 and PDF1.2. In contrast, disease symptom development in detached leaves appeared to be uncoupled from these defense pathways and more closely associated with senescence: an observation substantiated by coordinated gene expression analysis and disease symptom development, and chemically and genetically mimicking senescence.
authors.affiliation: Department of Biology, University of Saskatchewan, Saskatoon, S7N 5E2, Canada.
authors.forename: Guosheng
authors.initials: G
authors.lastname: Liu
authors.forename: Regan
authors.initials: R
authors.lastname: Kennedy
authors.forename: David L
authors.initials: DL
authors.lastname: Greenshields
authors.forename: Gary
authors.initials: G
authors.lastname: Peng
authors.forename: Lily
authors.initials: L
authors.lastname: Forseille
authors.forename: Gopalan
authors.initials: G
authors.lastname: Selvaraj
authors.forename: Yangdou
authors.initials: Y
authors.lastname: Wei
mesh_terms: D017360:Arabidopsis / Q000378:metabolism / Q000382:microbiology*; D029681:Arabidopsis Proteins / Q000378:metabolism; D020231:Colletotrichum / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D005030:Ethylenes / Q000378:metabolism; D007113:Immunity, Innate; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000378:metabolism / Q000382:microbiology*; D020156:Salicylic Acid / Q000378:metabolism; D015398:Signal Transduction; D014774:Virulence
chemical_list: D029681:Arabidopsis Proteins; D005030:Ethylenes; C489529:RCH1 protein, Arabidopsis; C036216:ethylene; D020156:Salicylic Acid