MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression in animals. This study shows that miRNAs are also present in plants, indicating that this class of RNA evolved early in eukaryotic evolution. The researchers identified 16 miRNAs in Arabidopsis, many of which are differentially expressed during development. Eight of these miRNAs are conserved in rice. The plant miRNA loci likely encode stem-loop precursors similar to those processed by Dicer in animals. Mutation of the Arabidopsis Dicer homolog, CARPEL FACTORY, prevents miRNA accumulation, showing that similar mechanisms direct miRNA processing in plants and animals. The study suggests that miRNAs may play regulatory roles in plant development, similar to their roles in animals. The miRNAs in plants are processed from double-stranded RNA precursors by Dicer, a ribonuclease III enzyme. The mature miRNAs are 20-24 nucleotides long and are derived from one arm of a stem-loop precursor. The study found that miRNAs in plants are evolutionarily conserved and have similar features to animal miRNAs. The presence of miRNAs in plants suggests that developmental defects in the CARPEL FACTORY mutant could result from miRNA processing defects. The study also found that miRNAs in plants are conserved in rice, indicating their importance in plant evolution. The study identified 16 miRNAs in Arabidopsis, which are named miR156 through miR171. These miRNAs are derived from different genomic regions and have varying expression patterns in different tissues. The study also found that miRNAs in plants can complement the coding regions of genes, suggesting they may regulate gene expression through this mechanism. The study highlights the importance of miRNAs in plant development and their potential roles in gene regulation. The findings suggest that miRNAs are an ancient class of non-coding RNAs that play a role in the regulation of gene expression in both plants and animals.MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression in animals. This study shows that miRNAs are also present in plants, indicating that this class of RNA evolved early in eukaryotic evolution. The researchers identified 16 miRNAs in Arabidopsis, many of which are differentially expressed during development. Eight of these miRNAs are conserved in rice. The plant miRNA loci likely encode stem-loop precursors similar to those processed by Dicer in animals. Mutation of the Arabidopsis Dicer homolog, CARPEL FACTORY, prevents miRNA accumulation, showing that similar mechanisms direct miRNA processing in plants and animals. The study suggests that miRNAs may play regulatory roles in plant development, similar to their roles in animals. The miRNAs in plants are processed from double-stranded RNA precursors by Dicer, a ribonuclease III enzyme. The mature miRNAs are 20-24 nucleotides long and are derived from one arm of a stem-loop precursor. The study found that miRNAs in plants are evolutionarily conserved and have similar features to animal miRNAs. The presence of miRNAs in plants suggests that developmental defects in the CARPEL FACTORY mutant could result from miRNA processing defects. The study also found that miRNAs in plants are conserved in rice, indicating their importance in plant evolution. The study identified 16 miRNAs in Arabidopsis, which are named miR156 through miR171. These miRNAs are derived from different genomic regions and have varying expression patterns in different tissues. The study also found that miRNAs in plants can complement the coding regions of genes, suggesting they may regulate gene expression through this mechanism. The study highlights the importance of miRNAs in plant development and their potential roles in gene regulation. The findings suggest that miRNAs are an ancient class of non-coding RNAs that play a role in the regulation of gene expression in both plants and animals.