title: A J domain virulence effector of Pseudomonas syringae remodels host chloroplasts and suppresses defenses.
abstract: BACKGROUND
  The plant pathogen Pseudomonas syringae injects 20-40 different proteins called effectors into host plant cells, yet the functions and sites of action of these effectors in promoting pathogenesis are largely unknown. Plants in turn defend themselves against P. syringae by activating the salicylic acid (SA)-mediated signaling pathway. The P. syringae-specific HopI1 effector has a putative chloroplast-targeting sequence and a J domain. J domains function by activating 70 kDa heat-shock proteins (Hsp70).
  
  
  RESULTS
  HopI1 is a ubiquitous P. syringae virulence effector that acts inside plant cells. When expressed in plants, HopI1 localizes to chloroplasts, the site of SA synthesis. HopI1 causes chloroplast thylakoid structure remodeling and suppresses SA accumulation. HopI1's C terminus has bona fide J domain activity that is necessary for HopI1-mediated virulence and thylakoid remodeling. Furthermore, HopI1-expressing plants have increased heat tolerance, establishing that HopI1 can engage the plant stress-response machinery.
  
  
  CONCLUSIONS
  These results strongly suggest that chloroplast Hsp70 is targeted by the P. syringae HopI1 effector to promote bacterial virulence by suppressing plant defenses. The targeting of Hsp70 function through J domain proteins is known to occur in a mammalian virus, SV40. However, this is the first example of a bacterial pathogen exploiting a J domain protein to promote pathogenesis through alterations of chloroplast structure and function.
authors.affiliation: Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Joanna
authors.initials: J
authors.lastname: Jelenska
authors.forename: Nan
authors.initials: N
authors.lastname: Yao
authors.forename: Boris A
authors.initials: BA
authors.lastname: Vinatzer
authors.forename: Christine M
authors.initials: CM
authors.lastname: Wright
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Brodsky
authors.forename: Jean T
authors.initials: JT
authors.lastname: Greenberg
mesh_terms: D017360:Arabidopsis / Q000378:metabolism / Q000382:microbiology; D001426:Bacterial Proteins / Q000032:analysis / Q000737:chemistry / Q000502:physiology*; D002736:Chloroplasts / Q000378:metabolism / Q000382:microbiology*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D018869:Heat-Shock Response; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000378:metabolism / Q000382:microbiology; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D044224:Pseudomonas syringae / Q000472:pathogenicity*; D020156:Salicylic Acid / Q000378:metabolism; D015398:Signal Transduction; D020524:Thylakoids / Q000378:metabolism / Q000382:microbiology; D014026:Nicotiana / Q000378:metabolism / Q000382:microbiology; D037521:Virulence Factors / Q000032:analysis / Q000737:chemistry / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D018840:HSP70 Heat-Shock Proteins; D037521:Virulence Factors; D020156:Salicylic Acid