title: MicroRNA-binding viral protein interferes with Arabidopsis development.
abstract: MicroRNAs (miRNAs) are small (approximately 21 nt), noncoding RNAs that negatively regulate target mRNAs at the posttranscriptional level that are involved in development. In plants, virus-induced disease symptoms often result in developmental abnormalities resembling perturbation of miRNA-mediated function. Here, we report that expression in transgenic plants of a geminivirus-encoded AC4 protein from African cassava mosaic virus Cameroon Strain (ACMV), a suppressor of posttranscriptional gene silencing, was correlated with decreased accumulation of host miRNAs and increased development abnormalities in Arabidopsis. Down-regulation of miRNA correlated with an up-regulation of target mRNA level. In vitro binding assays revealed the ability of AC4 of ACMV (A-AC4) but not East African cassava mosaic Cameroon virus AC2 to bind single-stranded forms of miRNAs and short interfering RNAs but not double-stranded RNA forms. Normally, a labile intermediate during the miRNA biogenesis/RNA-induced silencing complex assembly, miRNA*, was below the level of detection, indicating that AC4 might interfere at a point downstream of the miRNA duplex unwinding process. The association of AC4 with miRNA was demonstrated by the association of A-AC4-GFP fusion protein, extracted from Arabidopsis protoplasts, with 2'-O-methyloligonucleotide complementary to miR159 (miR159*) and by the presence of miRNA with the A-AC4-GFP fusion protein after immunoprecipitation with antibody against GFP. In both assays, A-AC4 protein and miRNA complexes were copurified. These results provide direct evidence that AC4 is a unique virus-encoded posttranscriptional gene-silencing suppressor protein that binds to and presumably inactivates mature miRNAs and thus blocks the normal miRNA-mediated regulation of target mRNAs, resulting in developmental defects in Arabidopsis.
authors: International Laboratory for Tropical Agricultural Biotechnology, Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, MO 63132, USA.
authors: Padmanabhan
authors: P
authors: Chellappan
authors: Ramachandran
authors: R
authors: Vanitharani
authors: Claude M
authors: CM
authors: Fauquet
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development*; D015152:Blotting, Northern; D017931:DNA Primers; D020868:Gene Silencing; D049452:Green Fluorescent Proteins; D047468:Immunoprecipitation; D035683:MicroRNAs / Q000378:metabolism*; D009029:Mosaic Viruses / Q000235:genetics*; D010935:Plant Diseases / Q000235:genetics / Q000821:virology*; D030821:Plants, Genetically Modified; D011485:Protein Binding; D013045:Species Specificity; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D035683:MicroRNAs; D014764:Viral Proteins; D049452:Green Fluorescent Proteins