title: Virus-encoded suppressor of posttranscriptional gene silencing targets a maintenance step in the silencing pathway.
abstract: Certain plant viruses encode suppressors of posttranscriptional gene silencing (PTGS), an adaptive antiviral defense response that limits virus replication and spread. The tobacco etch potyvirus protein, helper component-proteinase (HC-Pro), suppresses PTGS of silenced transgenes. The effect of HC-Pro on different steps of the silencing pathway was analyzed by using both transient Agrobacterium tumefaciens-based delivery and transgenic systems. HC-Pro inactivated PTGS in plants containing a preexisting silenced beta-glucuronidase (GUS) transgene. PTGS in this system was associated with both small RNA molecules (21-26 nt) corresponding to the 3' proximal region of the transcribed GUS sequence and cytosine methylation of specific sites near the 3' end of the GUS transgene. Introduction of HC-Pro into these plants resulted in loss of PTGS, loss of small RNAs, and partial loss of methylation. These results suggest that HC-Pro targets a PTGS maintenance (as opposed to an initiation or signaling) component at a point that affects accumulation of small RNAs and methylation of genomic DNA.
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA.
authors.forename: C
authors.initials: C
authors.lastname: Llave
authors.forename: K D
authors.initials: KD
authors.lastname: Kasschau
authors.forename: J C
authors.initials: JC
authors.lastname: Carrington
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000254:growth & development; D003433:Crosses, Genetic; D003546:Cysteine Endopeptidases / Q000235:genetics* / Q000378:metabolism*; D020868:Gene Silencing; D005822:Genetic Vectors; D005966:Glucuronidase / Q000235:genetics; D006720:Homozygote; D030821:Plants, Genetically Modified; D010947:Plants, Toxic; D017800:Potyvirus / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology; D018749:RNA, Plant / Q000235:genetics; D013489:Suppression, Genetic; D014026:Nicotiana / Q000235:genetics* / Q000821:virology*; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D018749:RNA, Plant; D014764:Viral Proteins; D005966:Glucuronidase; D003546:Cysteine Endopeptidases; C072775:HC-Pro protein, potyvirus