The splicing genes SmEa and SmEb regulate plant development during vegetative growth in poplar

Spliceosomes are large evolutionary conserved ribonucleoprotein complexes containing at their core heptameric rings of Sm (or LSm) proteins and U-rich snRNAs. The role of Sm proteins in animal development is well established, and recent research has begun to link mutations in these genes to growth defects in plants. One of the most studied Sm genes is SmE1/PCP, mutants of which display a temperature-dependent phenotype in Arabidopsis thaliana. This study provides a first glimpse into the function of a core splicing protein in the regulation of growth in a perennial species. Phylogenetic analysis identified two paralogous SmE genes in poplar, named SmEa and SmEb, that encode identical proteins and are orthologs of SmEs from Arabidopsis, as suggested by Y2H and in vivo experiments. CRISPR/Cas9 mutagenesis in hybrid aspen identified a role for SmEs in development in plants grown in an environment simulating seasonal photoperiod and temperature changes. Unlike in Arabidopsis, low temperatures had no or only a very minor effect on the development of sme mutants in aspen. We identified specific aspects of SmE in poplar, highlighting the importance of examining the physiological and evolutionary differences that define this gene family in woody compared to herbaceous plants.