title: Citrus tristeza virus p23: determinants for nucleolar localization and their influence on suppression of RNA silencing and pathogenesis.
abstract: Citrus tristeza virus (CTV) encodes a singular protein (p23, 209 amino acids) with multiple functions, including RNA silencing suppression (RSS). Confocal laser-scanning microscopy of green fluorescent protein (GFP)-p23 agroexpressed in Nicotiana benthamiana revealed its accumulation in the nucleolus, Cajal bodies, and plasmodesmata. To dissect the nucleolar localization signal (NoLS) typically associated with basic motifs, seven truncated and 10 point-mutated versions of p23 were assayed. Deletion mutants showed that regions 50 to 86 and 100 to 157 (excluding fragment 106 to 114), both with basic motifs and the first with a zinc-finger, contain the (bipartite) NoLS. Alanine substitutions delimited this signal to three cysteines of the Zn-finger and some basic amino acids. RSS activity of p23 in N. benthamiana was abolished by essentially all mutants, indicating that it involves most p23 regions. The necrotic-inducing ability of p23 when launched in N. benthamiana from Potato virus X was only retained by deletion mutant 158-209 and one substitution mutant, showing that the Zn-finger and flanking basic motifs form part of the pathogenic determinant. Ectopic expression of p23 and some deletion mutants in transgenic Mexican lime demarcated a similar determinant, suggesting that p23 affects related pathways in citrus and N. benthamiana. Both RSS activity and pathogenicity of p23 appear related to its nucleolar localization.
authors: Consejo Superior de Investigaciones Cientificas-Universidad Politecnica de Valencia, Spain.
authors: Susana
authors: S
authors: Ruiz-Ruiz
authors: Nuria
authors: N
authors: Soler
authors: Jesús
authors: J
authors: Sánchez-Navarro
authors: Carmen
authors: C
authors: Fagoaga
authors: Carmelo
authors: C
authors: López
authors: Luis
authors: L
authors: Navarro
authors: Pedro
authors: P
authors: Moreno
authors: Leandro
authors: L
authors: Peña
authors: Ricardo
authors: R
authors: Flores
mesh_terms: D021581:Active Transport, Cell Nucleus; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002466:Cell Nucleolus / Q000378:metabolism*; D002957:Citrus / Q000166:cytology / Q000821:virology*; D017790:Closterovirus / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D020541:Coiled Bodies / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000737:chemistry; D054884:Host-Pathogen Interactions; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000821:virology*; D018515:Plant Leaves / Q000166:cytology / Q000821:virology; D030821:Plants, Genetically Modified; D031425:Plasmodesmata / Q000378:metabolism; D017354:Point Mutation; D017863:Potexvirus / Q000235:genetics; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D017384:Sequence Deletion; D014026:Nicotiana / Q000166:cytology / Q000821:virology*; D019076:Transgenes; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*; D014774:Virulence
chemical_list: D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D049452:Green Fluorescent Proteins