title: The helicase domain of the TMV replicase proteins induces the N-mediated defence response in tobacco.
abstract: Tobacco mosaic virus (TMV) induces the hypersensitive response (HR) in tobacco plants containing the N gene. This defence response is characterized by cell death at the site of virus infection and inhibition of viral replication and movement. A previous study indicated that a portion of the TMV replicase containing a putative helicase domain is involved in HR induction. Here, this observation is confirmed and extended by showing that non-viral expression of a 50 kDa TMV helicase fragment (p50) is sufficient to induce the N-mediated HR in tobacco. Like the HR elicited by TMV infection, transgenic expression of p50 induces a temperature-sensitive defence response. We demonstrate that recombinant p50 protein has ATPase activity, as suggested by the presence of conserved sequence motifs found in ATPase/helicase enzymes. A point mutation that alters one of these motifs abolishes ATPase activity in vitro but does not affect HR induction. These results suggest that features of the TMV helicase domain, independent of its enzymatic activity, are recognized by N-containing tobacco to induce TMV resistance.
authors.affiliation: Plant Gene Expression Center, University of California, Berkeley, USA.
authors.forename: F L
authors.initials: FL
authors.lastname: Erickson
authors.forename: S
authors.initials: S
authors.lastname: Holzberg
authors.forename: A
authors.initials: A
authors.lastname: Calderon-Urrea
authors.forename: V
authors.initials: V
authors.lastname: Handley
authors.forename: M
authors.initials: M
authors.lastname: Axtell
authors.forename: C
authors.initials: C
authors.lastname: Corr
authors.forename: B
authors.initials: B
authors.lastname: Baker
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D017343:Genes, Plant; D005814:Genes, Viral; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D020365:RNA Helicases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012231:Rhizobium / Q000235:genetics; D013696:Temperature; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics / Q000821:virology*; D014027:Tobacco Mosaic Virus / Q000201:enzymology* / Q000472:pathogenicity
chemical_list: C085103:tobacco mosaic virus replicase; D012324:RNA-Dependent RNA Polymerase; D000251:Adenosine Triphosphatases; D020365:RNA Helicases