title: Localization of DIR1 at the tissue, cellular and subcellular levels during Systemic Acquired Resistance in Arabidopsis using DIR1:GUS and DIR1:EGFP reporters.
abstract: BACKGROUND
  Systemic Acquired Resistance (SAR) is an induced resistance response to pathogens, characterized by the translocation of a long-distance signal from induced leaves to distant tissues to prime them for increased resistance to future infection. DEFECTIVE in INDUCED RESISTANCE 1 (DIR1) has been hypothesized to chaperone a small signaling molecule to distant tissues during SAR in Arabidopsis.
  
  
  RESULTS
  DIR1 promoter:DIR1-GUS/dir1-1 lines were constructed to examine DIR1 expression. DIR1 is expressed in seedlings, flowers and ubiquitously in untreated or mock-inoculated mature leaf cells, including phloem sieve elements and companion cells. Inoculation of leaves with SAR-inducing avirulent or virulent Pseudomonas syringae pv tomato (Pst) resulted in Type III Secretion System-dependent suppression of DIR1 expression in leaf cells. Transient expression of fluorescent fusion proteins in tobacco and intercellular washing fluid experiments indicated that DIR1's ER signal sequence targets it for secretion to the cell wall. However, DIR1 expressed without a signal sequence rescued the dir1-1 SAR defect, suggesting that a cytosolic pool of DIR1 is important for the SAR response.
  
  
  CONCLUSIONS
  Although expression of DIR1 decreases during SAR induction, the protein localizes to all living cell types of the vasculature, including companion cells and sieve elements, and therefore DIR1 is well situated to participate in long-distance signaling during SAR.
authors: Department of Biology, McMaster University, Hamilton, ON L8S 4K1 Canada.
authors: Marc J
authors: MJ
authors: Champigny
authors: Heather
authors: H
authors: Shearer
authors: Asif
authors: A
authors: Mohammad
authors: Karen
authors: K
authors: Haines
authors: Melody
authors: M
authors: Neumann
authors: Roger
authors: R
authors: Thilmony
authors: Sheng Yang
authors: SY
authors: He
authors: Pierre
authors: P
authors: Fobert
authors: Nancy
authors: N
authors: Dengler
authors: Robin K
authors: RK
authors: Cameron
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000276:immunology* / Q000382:microbiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D060467:Disease Resistance; D050556:Fatty Acid-Binding Proteins; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D057865:Plant Immunity; D018515:Plant Leaves / Q000235:genetics / Q000276:immunology / Q000382:microbiology; D030821:Plants, Genetically Modified / Q000276:immunology / Q000382:microbiology; D011401:Promoter Regions, Genetic; D044224:Pseudomonas syringae / Q000472:pathogenicity; D018749:RNA, Plant / Q000235:genetics; D036226:Seedlings / Q000235:genetics / Q000276:immunology / Q000382:microbiology; D014026:Nicotiana
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D050556:Fatty Acid-Binding Proteins; D018749:RNA, Plant; C466483:dir1-1 protein, Arabidopsis