Alternative splicing is an important posttranscriptional gene regulatory process, acting in diverse adaptive and basal plant processes. Splicing of precursor-messenger RNA (pre-mRNA) is catalyzed by a dynamic ribonucleoprotein complex, termed the spliceosome. In a suppressor screen, we identified a nonsense mutation in the Sm protein SME1 to alleviate photorespiratory H2O2-dependent cell death in catalase-deficient plants. Furthermore, sme1-2 mutants showed increased tolerance to the superoxide-generating herbicide methyl viologen. mRNA-seq and proteomic analyses indicated a constitutive stress response and pre-mRNA splicing alterations in sme1-2 mutants under control conditions. With a pulldown experiment, using SME1 as a bait, we provide experimental evidence for proteins associated with Arabidopsis thaliana spliceosome complexes, by identifying almost 50 proteins homologous to mammalian spliceosome-associated proteins and propose four novel proteins previously not-reported or hypothesized to be part of plant spliceosome complexes. Mutation of one of these interactors, the Sm core assembly protein ICLN also resulted in a decreased sensitivity to methyl viologen. Taken together, we show that SME1 mutation and impaired snRNP assembly result in enhanced resilience to oxidative stress.