Disease relevance of AGO1

• A recent study by Zhang and colleagues1 now shows that the 2b suppressor of Cucumber mosaic virus directly interacts with Arabidopsis AGO1 and inhibits its slicing activity, suggesting that AGO1 might be a component of the elusive plant antiviral RISC [1].
• The defect in adventitious rooting observed in ago1 correlated with light hypersensitivity and the deregulation of auxin homeostasis specifically in the apical part of the seedlings [2].
• As opposed to rde-1 and qde-2 mutants, which are viable, ago1 mutants display several developmental abnormalities, including sterility [3].

High impact information on AGO1

• We conclude that 2b blocks AGO1 cleavage activity to inhibit miRNA pathways, attenuate RNA silencing, and counter host defense [4].
• Loss-of-function mutations in these genes have a phenotype similar to that of mutations in the Argonaute gene ZIPPY (ZIP) [5].
• AGO1 homeostasis entails coexpression of MIR168 and AGO1 and preferential stabilization of miR168 by AGO1 [6].
• In Arabidopsis, except for AGO1, AGO4 and AGO7, the roles of seven other AGOs in gene silencing are not known [7].
• Similar proteins are not encoded by the genomes of yeast or bacteria, suggesting that AGO1 belongs to a novel class of genes with a function specific to multicellular organisms [8].

Biological context of AGO1

• Mutations in AGO1 severely disrupt plant development, indicating that miRNA function and possibly other aspects of RNA interference are essential for maintaining normal patterns of gene expression [9].
• ARGONAUTE1 (AGO1) of Arabidopsis thaliana mediates the cleavage of microRNA (miRNA)-targeted mRNAs, and it has also been implicated in the posttranscriptional silencing of transgenes and the maintenance of chromatin structure [9].
• MicroRNA-targeted and small interfering RNA-mediated mRNA degradation is regulated by argonaute, dicer, and RNA-dependent RNA polymerase in Arabidopsis [9].
• The ARGONAUTE gene family is involved in the regulation of gene expression via the RNAi Silencing Complex (RISC). microRNA (miRNA) are 20-22bp RNAs that direct RISC to target genes [10].
• The AGO1 locus was mapped close to the marker mi291a on chromosome 1 [8].

Anatomical context of AGO1

• Through phenotypic and double mutant analysis, we show that AGO1 regulates stem cell function via SHOOT MERISTEMLESS (STM) [10].

Associations of AGO1 with chemical compounds

• Auxin and light control of adventitious rooting in Arabidopsis require ARGONAUTE1 [2].
• In addition, interactions between homeodomain/leucine zipper genes and an allelic series of ago1 indicate that miRNA acts as a signal to specify leaf polarity [11].

Regulatory relationships of AGO1

• CLF is over expressed in ago1, showing that the RNAi pathway regulates polycomb-type epigenetic modifiers [10].
• Thus, we suggest that ARF17 negatively regulates adventitious root formation in ago1 mutants by repressing GH3 genes and therefore perturbing auxin homeostasis in a light-dependent manner [2].

Other interactions of AGO1

• Conversely, a mutation in ZWILLE/PINHEAD, another member of the Arabidopsis AGO1 gene family, affects development but not PTGS [12].
• Proteins of the Dicer-Like and Argonaute (AGO) families have key roles within these silencing pathways and have distinct biochemical properties [13].
• A DNA VIGS vector derived from CaLCuV, which silenced chlorata42 (ChlI) needed for chlorophyll formation, was used to test endogenous gene silencing responses in suppressor of gene silencing (sgs)1, sgs2, sgs3, and Argonaute (ago)1 mutants defective in sense transgene-mediated post-transcriptional silencing (S-PTGS) [14].
• The Arabidopsis heterochronic gene ZIPPY is an ARGONAUTE family member [15].

References