DROL1 subunit of U5 snRNP in the spliceosome is specifically required to splice AT--AC-type introns in Arabidopsis

Abstract

An Arabidopsis mutant named defective repression of OLE3::LUC 1 (drol1) was originally isolated as a mutant with defects in the repression of OLEOSIN3 (OLE3) after seed germination. In this study, we show that DROL1 is an Arabidopsis homolog of yeast DIB1, a subunit of U5 snRNP in the spliceosome. It is also part of a new subfamily that is specific to a certain class of eukaryotes. Comprehensive analysis of the intron splicing using RNA-Seq analysis of the drol1 mutants revealed that most of the minor introns with AT-AC dinucleotide termini had reduced levels of splicing. Only two nucleotide substitutions from AT-AC to GT-AG enabled AT-AC-type introns to be spliced in drol1 mutants. Forty-eight genes, including those having important roles in abiotic stress responses and cell proliferation, exhibited reduced splicing of AT-AC-type introns in the drol1 mutants. Additionally, drol1 mutant seedlings showed retarded growth, similar to that caused by the activation of abscisic acid signaling, possibly as a result of reduced AT-AC-type intron splicing in the endosomal Na+/H+ antiporters and plant-specific histone deacetylases. These results indicate that DROL1 is specifically involved in the splicing of minor introns with AT-AC termini, and that this plays an important role in plant growth and development. Significance statementDefective Repression of OLE3::LUC 1 (DROL1) is a homolog of yeast DIB1, which is a subunit of the U5 snRNP in the spliceosome, but is also part of a new subfamily that is specific to a certain class of eukaryotes. Using RNA-Seq we show that introns with AT-AC dinucleotide termini were specifically retained in the transcriptome of drol1 mutants and that their splicing plays an important role in plant growth and development.