A method for inhibiting the expression of a gene comprising introducing into a plant cell or a non-human animal or cell isolated a DNA construct comprising a constitutive promoter or functional inducible in said cell I operably linked to a nucleic acid comprises a nucleotide sequence encoding, as part of a longer sequence encoded a precursor miRNA said precursor miRNA comprising troncobucle structure and comprising in said frustum of said structure troncobucle a sequence complementary to a part of an RNA transcript of said gene, wherein said trunk of said trunk-loop structure has a length of approximately 19-45 base pairs and said loop-loop trunk structure comprises about 4-25 nucleotides, wherein, after introducing said construct into said cell: (i) said nucleotide sequence is transcribed, (ii) the transcript re sultante of said nucleotide sequence is processed so that said precursor miRNA is cleaved from said transcript of said nucleotide sequence, (iii) said precursor miRNA is processed so that a mature miRNA about 21 or 22 nucleotides in length cleaving said precursor miRNA, and (iv) inhibition of expression of said gene is performed.Un método para inhibir la expresión de un gen que comprende introducir en una célula vegetal o en una célula humana o animal no humana aisladas una construcción de ADN que comprende un promotor constitutivo o inducible funcional en dicha célula unido de forma funcional a un ácido nucleico que comprende una secuencia de nucleótidos que codifica, como parte de una secuencia codificada más larga, un precursor de miARN, comprendiendo dicho precursor de miARN una estructura de tronco-bucle y comprendiendo en dicho tronco de dicha estructura de troncobucle una secuencia complementaria a una parte de un transcrito de ARN de dicho gen, donde dicho tronco de dicha estructura de tronco-bucle tiene una longitud de aproximadamente 19-45 pares de bases y el bucle de dicha estructura de tronco-bucle comprende aproximadamente 4-25 nucleótidos, don
