Aberrant splicing in maize <i>rough endosperm3</i> reveals a conserved role for U12 splicing in eukaryotic multicellular development

Abstract

RNA splicing of U12-type introns functions in human cell differentiation, but it is not known whether this class of introns has a similar role in plants. The maize ROUGH ENDOSPERM3 (RGH3) protein is orthologous to the human splicing factor, ZRSR2. <i>ZRSR2</i> mutations are associated with myelodysplastic syndrome (MDS) and cause U12 splicing defects. Maize <i>rgh3</i> mutants have aberrant endosperm cell differentiation and proliferation. We found that most U12-type introns are retained or misspliced in <i>rgh3</i> Genes affected in <i>rgh3</i> and <i>ZRSR2</i> mutants identify cell cycle and protein glycosylation as common pathways disrupted. Transcripts with retained U12-type introns can be found in polysomes, suggesting that splicing efficiency can alter protein isoforms. The <i>rgh3</i> mutant protein disrupts colocalization with a known ZRSR2-interacting protein, U2AF2. These results indicate conserved function for RGH3/ZRSR2 in U12 splicing and a deeply conserved role for the minor spliceosome to promote cell differentiation from stem cells to terminal fates.