LUC7 is an U1snRNP component that plays a role in alternative splicing and terminal introns removal in plants

Introns are removed by the spliceosome, a large complex composed of five ribonucleoprotein subcomplexes (U snRNP). In metazoans, the U1 snRNP, which binds to 5' splice sites, also fulfills regulatory roles in splice site selection and possesses non-splicing related functions. Here, we show that an Arabidopsis U1 snRNP subunit, LUC7, affects constitutive and alternative splicing. Interestingly, LUC7 specifically promotes splicing of a subset of terminal introns. Splicing of LUC7-dependent terminal introns is a prerequisite for nuclear export and can be modulated by stress. Globally, intron retention under stress conditions occurs preferentially among first and terminal introns, uncovering an unknown bias for splicing regulation in Arabidopsis. Taken together, our study reveals that the Arabidopsis U1 snRNP is important for alternative splicing and removal of terminal introns and it suggests that Arabidopsis terminal introns fine-tune gene expression under stress conditions. Overall design: Poly A libraries from wild type plants (WT Col-0) and a triple mutant (luc7 a-2, b-1, rl-1) were performed in triplicates