Arabidopsis thaliana cultivar:Columbia Transcriptome or Gene expression

The debranching enzyme (DBR) is a conserved enzyme in eukaryotes that linearizes lariat RNAs formed as by-products of splicing to lead to their degradation. DBR is also necessary for the biogenesis of mirtron miRNAs, a class of nonconventional miRNAs that resides in introns and relies on splicing rather than the microprocessor for biogenesis. DBR is not known to affect the biogenesis of conventional miRNAs in either animals or plants. Here, we isolated and characterized a weak mutant allele of the DBR1 gene in Arabidopsis. In the dbr1 mutant, a global increase in lariat RNAs was unexpectedly accompanied by a global reduction in miRNA accumulation. Lariat RNAs were found to co-localize with the DCL1/HYL1 complex in the nucleus, and the dbr1 mutant exhibited defects in the subcellular localization of both DCL1 and HYL1. We propose that lariat RNAs act as decoys to inhibit miRNA homeostasis. The presence of lariat RNAs even in the wild-type background suggests that they may represent a previously unknown layer of regulation in miRNA biogenesis.