The Arabidopsis U1 snRNP regulates mRNA 3'-end processing

The removal of introns by the splicesome is a key gene regulatory mechanism in eukaryotes and is initiated by the U1 snRNPs subunit of the spliceosome. Studies in metazoans show that the U1 snRNP also conducts splicing-independent functions, but the lack of genetic tools and knowledge about U1 snRNP associated proteins has limited to study such splicing independent function in plants. Here, we describe an RNA-centric approach that identified more than 200 proteins associated the Arabidopsis U1 snRNP, among them components in mRNA cleavage and polyadenylation. Loss of function of U1 core components is associated with premature polyadenylation in gene bodies and alternative polyA-site selection in 3'UTRs. Overall, our work provides a comprehensive view of U1 snRNP interactors and reveals novel functions in regulating mRNA 3' end processing in Arabidopsis, thus establishing the groundwork for a better understanding of non-canonical functions of plant U1 snRNPs.