摘要
Trans-acting small interfering RNAs （ta-siRNAs） are plant-specific siRNAs released from TAS precursor tran- scripts after microRNA-dependent cleavage, conversion into double-stranded RNA, and Dicer-dependent phased process- ing. Like microRNAs （miRNAs）, ta-siRNAs direct site-specific cleavage of target RNAs at sites of extensive complementarity. Here, we show that the DICER-LIKE 4 protein of Physcomitrella patens （PpDCL4） is essential for the biogenesis of 21 nucleotide （nt） ta-siRNAs. In APpDCL4 mutants, off-sized 23 and 24-nt ta-siRNAs accumulated as the result of PpDCL3 activity. APpDCL4 mutants display severe abnormalities throughout Physcomitrella development, including sterility, that were fully reversed in APpDCL3/APpDCL4 double-mutant plants. Therefore, PpDCL3 activity, not loss of PpDCL4 function per se, is the cause of the APpDCL4 phenotypes. Additionally, we describe several new Physcomitrella trans-acting siRNA loci, three of which belong to a new family, TA56. TAS6 loci are typified by sliced miR156 and miR529 target sites and are in close proximity to PpTAS3 loci.
Trans-acting small interfering RNAs （ta-siRNAs） are plant-specific siRNAs released from TAS precursor tran- scripts after microRNA-dependent cleavage, conversion into double-stranded RNA, and Dicer-dependent phased process- ing. Like microRNAs （miRNAs）, ta-siRNAs direct site-specific cleavage of target RNAs at sites of extensive complementarity. Here, we show that the DICER-LIKE 4 protein of Physcomitrella patens （PpDCL4） is essential for the biogenesis of 21 nucleotide （nt） ta-siRNAs. In APpDCL4 mutants, off-sized 23 and 24-nt ta-siRNAs accumulated as the result of PpDCL3 activity. APpDCL4 mutants display severe abnormalities throughout Physcomitrella development, including sterility, that were fully reversed in APpDCL3/APpDCL4 double-mutant plants. Therefore, PpDCL3 activity, not loss of PpDCL4 function per se, is the cause of the APpDCL4 phenotypes. Additionally, we describe several new Physcomitrella trans-acting siRNA loci, three of which belong to a new family, TA56. TAS6 loci are typified by sliced miR156 and miR529 target sites and are in close proximity to PpTAS3 loci.
