Methylosome and SMN complexes are dispensable for snRNP assembly in Arabidopsis

ABSTRACT The role of RNA splicing as modulator of the molecular responses to stress is well described. In contrast, its importance in the acclimation of plants to changes in ambient temperatures started to emerge only recently. Here, we analyzed the role of temperature in spliceosome assembly, a key step often neglected in studies focusing on 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 snRNP assembly. Genetic analyses, as well as in vivo and in vitro evidence suggest a mechanism for snRNP assembly in plants that differs remarkably from vertebrate animals. The SMN complex in plants is apparently reduced to a single protein, GEMIN2, that is not essential for plant development. Similarly, the methylosome has a less crucial role in spliceosome assembly than previously thought. Our results highlight how an evolutionary conserved molecular process like RNA splicing has nevertheless evolved plant specific characteristics.