The action of <i>ARGONAUTE1</i> in the miRNA pathway and its regulation by the miRNA pathway are crucial for plant development

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<jats:p>MicroRNAs (miRNAs) are endogenous 21–24-nt RNAs that can down-regulate gene expression by pairing to the messages of protein-coding genes to specify mRNA cleavage or repression of productive translation. They act within the RNA-induced silencing complex (RISC), which in animals contains a member of the Argonaute family of proteins. In the present study, we show that <jats:italic>Arabidopsis ago1</jats:italic> mutants have increased accumulation of mRNAs known to be targeted for cleavage by miRNAs. In hypomorphic <jats:italic>ago1</jats:italic> alleles, this compromised miRNA function occurs without a substantial change in miRNA accumulation, whereas in null alleles it is accompanied by a drop in some of the miRNAs. Therefore, AGO1 acts within the <jats:italic>Arabidopsis</jats:italic> miRNA pathway, probably within the miRNA-programmed RISC, such that the absence of AGO1 destabilizes some of the miRNAs. We also show that targeting of <jats:italic>AGO1</jats:italic> mRNA by miR168 is needed for proper plant development, illustrating the importance of feedback control by this miRNA. Transgenic plants expressing a mutant <jats:italic>AGO1</jats:italic> mRNA with decreased complementarity to miR168 overaccumulate <jats:italic>AGO1</jats:italic> mRNA and exhibit developmental defects partially overlapping with those of <jats:italic>dcl1</jats:italic>, <jats:italic>hen1</jats:italic>, and <jats:italic>hyl1</jats:italic> mutants showing a decrease in miRNA accumulation. miRNA targets overaccumulate in miR168-resistant plants, suggesting that a large excess of AGO1 protein interferes with the function of RISC or sequesters miRNAs or other RISC components. Developmental defects induced by a miR168-resistant <jats:italic>AGO1</jats:italic> mRNA can be rescued by a compensatory miRNA that is complementary to the mutant <jats:italic>AGO1</jats:italic> mRNA, proving the regulatory relationship between miR168 and its target and opening the way for engineering artificial miRNAs in plants.</jats:p>

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  • Genes & Development

    Genes & Development 18 (10), 1187-1197, 2004-05-06

    Cold Spring Harbor Laboratory

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