Methylosome and SMN complexes are dispensable for plant viability in Arabidopsis thaliana

The role of RNA splicing as a modulator of the molecular responses to stress is well described. In contrast, its importance in the acclimation of plants to changes in ambient temperatures has only recently started to emerge. Here, we analyzed the role of temperature in regulating the functionality of factors associated with snRNP biogenesis, a key process underlying pre-mRNA splicing. Taking advantage of mutants showing temperature-dependent phenotypes, we conducted a comprehensive study of the role that the methylosome and SMN complexes have in plant development. Genetic, phylogenetic, and confocal analyses, as well as in vivo and in vitro evidence, reveal remarkable differences in the composition and importance of these complexes between plants and vertebrate animals. The SMN complex in Arabidopsis is apparently reduced to a single protein, GEMIN2, that is not essential for plant development, and the existence of a SMN ortholog is uncertain. Similarly, components of the methylosome previously implicated in snRNP biogenesis are not essential for plant viability. Our results suggest that factors considered central to snRNP biogenesis in animals have less crucial roles in plants and highlight how an evolutionarily conserved molecular process like RNA splicing has nevertheless evolved plant specific characteristics.