22nt

22nt refers to RNA molecules that are 22 nucleotides in length, a size class within the broader family of small regulatory RNAs that range from about 21 to 24 nucleotides. These small RNAs play central roles in RNA interference pathways, guiding gene expression regulation by associating with Argonaute proteins and directing target silencing.

In plants, 22-nt small RNAs are often derived from Dicer-like enzymes such as DCL2 and can initiate amplification of silencing through RNA-dependent RNA polymerase 6 (RDR6). This amplification leads to the production of secondary small interfering RNAs, including trans-acting siRNAs (ta-siRNAs) and phased secondary siRNAs (phasiRNAs), which extend silencing beyond the original target. The 22-nt length can influence the mode of action, with certain 22-nt miRNAs capable of triggering these secondary pathways when loaded into appropriate Argonaute proteins, such as AGO1.

The distinction between 22-nt and other nearby length classes (notably 21-nt and 24-nt) reflects differences in biogenesis and downstream effects. For example, 21-nt and 24-nt species are often associated with direct cleavage or transcriptional silencing, respectively, whereas 22-nt species are particularly notable for their potential to initiate amplification cascades in plant systems. The exact prevalence and function of 22-nt RNAs can vary among species, tissues, and developmental stages, and research continues to clarify their production, loading preferences, and regulatory impact.

Overall, 22nt represents a specific size category of small RNAs with characteristic implications for gene silencing and regulatory network dynamics, especially in plant RNA silencing pathways.