DICER-LIKE3 Activity in Physcomitrella patens DICER-LIKE4 Mutants Causes Severe Developmental Dysfunction and Sterility

摘要

Trans-acting small interfering RNAs (ta-siRNAs) are plant-specific siRNAs released from TAS precursor transcripts after microRNA-dependent cleavage,conversion into double-stranded RNA,and Dicer-dependent phased processing.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 △PpDCL4 mutants,off-sized 23 and 24-nt ta-siRNAs accumulated as the result of PpDCL3 activity,△PpDCL4 mutants display severe abnormalities throughout Physcomitrella development,including sterility,that were fully reversed in △PpDCL3/△PpDCL4 double-mutant plants.Therefore,PpDCL3 activity,not loss of PpDCL4 function per se,is the cause of the △PpDCL4 phenotypes.Additionally,we describe several new Physcomitrella trans-acting siRNA loci,three of which belong to a new family,TAS6.TAS6 loci are typified by sliced miR156 and miR529 target sites and are in close proximity to PpTAS3 loci.