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Small nuclear RNAs (snRNAs) are the basal components of the spliceosome and play crucial roles in splicing. Their biogenesis is spatiotemporally regulated. However, related mechanisms are still poorly understood. Defective in snRNA processing (DSP1) is an essential component of the DSP1 complex that catalyzes plant snRNA 3′-end maturation by cotranscriptional endonucleolytic cleavage of the primary snRNA transcripts (presnRNAs). Here, we show thatDSP1is subjected to alternative splicing in pollens and embryos, resulting in two splicing variants,DSP1α andDSP1β. Unlike DSP1α, DSP1β is not required for presnRNA 3′-end cleavage. Rather, it competes with DSP1α for the interaction with CPSF73-I, the catalytic subunit of the DSP1 complex, which promotes efficient release of CPSF73-I and the DNA-dependent RNA polymerease II (Pol II) from the 3′ end of snRNA loci thereby facilitates snRNA transcription termination, resulting in increased snRNA levels in pollens. Taken together, this study uncovers a mechanism that spatially regulates snRNA accumulation.

 

mall nuclear RNAs (snRNAs) play essential roles in spliceosome assembly and splicing. Most snRNAs are transcribed by the DNA-dependent RNA polymerase II (Pol II) and require 3' end endonucleolytic cleavage. We have previously shown that the Arabidopsis (Arabidopsis thaliana) Defective in snRNA Processing 1 (DSP1) complex, composed of at least five subunits, is responsible for snRNA 3' maturation and is essential for plant development. Yet, it remains unclear how DSP1 complex subunits act together to process snRNAs. Here we show that DSP4, a member of the metallo-β-lactamase family, physically interacts with DSP1 through its β-Casp domain. Null dsp4-1 mutants have pleiotropic developmental defects, including impaired pollen development, and reduced pre-snRNA transcription and 3' maturation, resembling the phenotype of the dsp1-1 mutant. Interestingly, dsp1-1 dsp4-1 double mutants exhibit complete male sterility and reduced pre-snRNA transcription and 3' end maturation, unlike dsp1-1 or dsp4-1. In addition, Pol II occupancy at snRNA loci is lower in dsp1-1 dsp4-1 than in either single mutant. We also detected miscleaved pre-snRNAs in dsp1-1 dsp4-1, but not in dsp1-1 or dsp4-1. Taken together, these data reveal that DSP1 and DSP4 function is essential for pollen development, and that the two cooperatively promote pre-snRNA transcription and 3' end processing efficiency and accuracy.