Abstract
Introns are removed by the spliceosome, a large macromolecular complex composed of five ribonucleoprotein subcomplexes (U snRNP). The U1 snRNP, which binds to 5’ splice sites, plays an essential role in early steps of the splicing reaction. Here, we show that Arabidopsis LUC7 proteins are U1 snRNP accessory components important for plant development and stress resistance. Transcriptome analyses revealed that LUC7 proteins are not only important for constitutive splicing, but also affect hundreds of alternative splicing events. Interestingly, LUC7 proteins specifically promote splicing of a subset of terminal introns. Splicing of LUC7-dependent terminal introns is a prerequisite for nuclear export and some splicing events are modulated by stress in a LUC7-dependent manner. Taken together our results highlight the importance of the U1 snRNP component LUC7 in splicing regulation and suggest a previously unrecognized contribution of terminal introns splicing in plant stress responses.