Abstract
Trans-acting small interfering RNAs (tasiRNAs) are plant-specific endogenous siRNAs that control non-identical mRNAs via cleavage. The production of tasiRNAs is triggered by cleavage of capped and polyadenylated primary TAS transcripts (pri-TASs) by specific miRNAs. Following miRNA-directed cleavage, either 5' or 3' cleavage fragments are converted into double-stranded RNAs (dsRNAs) by RNA-DEPENDENT RNA POLYMERASE 6. The dsRNAs are processed to tasiRNAs by DICER-LIKE 4 in a phasing manner. There are two forms of pri-TASs; One has a single miRNA target site that is targeted by 22-nucleotide microRNAs, and the other has two miR390 target sites. Secondary siRNAs that are important for the amplification of RNA silencing are defined as siRNAs whose production is initiated by the cleavage of primary small RNA-containing RNA-induced silencing complexes. Thus, tasiRNA production is a model system of secondary siRNA production in plants. This review focuses on the production of tasiRNAs that are endogenous secondary siRNAs.
Highlights
Phenomena that were previously described as RNA interference in nematodes, quelling in fungi, or co-suppression in plants can be attributed to small RNA-mediated sequence-specific gene regulation (Hannon, 2002)
Dicer proteins generate 20–25 nucleotide small RNA (sRNA) duplexes from double-stranded precursor RNAs. sRNAs produced by Dicer can be divided into two types based on the precursor RNAs: microRNAs or small interfering RNAs. miRNAs are excised from single-stranded RNAs that form fold-back structures containing partially doublestranded regions
Genes have been identified via extensive genetic screenings for susceptibility to viruses in Arabidopsis plants, the release of S-PTGS and developmental abnormality, and analyses have uncovered the molecular functions of those genes in tasiRNA production
Summary
Trans-acting small interfering RNAs (tasiRNAs) are plant-specific endogenous siRNAs that control non-identical mRNAs via cleavage. The production of tasiRNAs is triggered by cleavage of capped and polyadenylated primary TAS transcripts (pri-TASs) by specific miRNAs. Following miRNA-directed cleavage, either 5′ or 3′ cleavage fragments are converted into double-stranded RNAs (dsRNAs) by RNADEPENDENT RNA POLYMERASE 6. The dsRNAs are processed to tasiRNAs by DICER-LIKE 4 in a phasing manner. Secondary siRNAs that are important for the amplification of RNA silencing are defined as siRNAs whose production is initiated by the cleavage of primary small RNA-containing RNA-induced silencing complexes. TasiRNA production is a model system of secondary siRNA production in plants. This review focuses on the production of tasiRNAs that are endogenous secondary siRNAs
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