Trans-acting siRNA is a form of small interfering RNA

Small interfering RNA

Small interfering RNA , sometimes known as short interfering RNA or silencing RNA, is a class of double-stranded RNA molecules, 20-25 nucleotides in length, that play a variety of roles in biology. The most notable role of siRNA is its involvement in the RNA interference pathway, where it...

 (siRNA) that represses gene expression

Gene expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

 through post-transcriptional gene silencing in land plants, , . It is transcribed from the genome to form a polyadenylated, double-stranded precursor. Unlike other siRNAs, but like microRNA, ta-siRNA does not require full complementarity to its target RNA to have an effect.