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Abstract

The molecular mechanism of miRNA action requires complementary basepairing
between miRNA molecules and target mRNAs. In animals, where
the primary mode of miRNA action is translational repression, there is only
modest complementarity between miRNAs and their targets. In plants, it
appears that most miRNAs can trigger cleavage of target mRNAs similar to
perfectly complementary siRNAs (short interfering RNAs). For this reason,
computational identification of miRNA targets has focused on a high degree
of complementarity to the miRNA (0-3 mismatches). Many predicted targets
have been verified in vitro, some also in vivo, mostly by showing that the
targets are indeed cleaved. However, there are also experimentally verified
examples of targets with more than 4 mismatches, which can still be cleaved
in a siRNA-related manner.
We have been asking for common rules of functional miRNA target
sequences in Arabidopsis thaliana. For that purpose we created several
transgenic lines overexpressing miRNAs from different families. Genomewide
expression changes have been analyzed in the overexpression lines.
Inferences from these experiments will be presented.