Abstract
Correct gene expression requires tight RNA quality control both at transcriptional and post-transcriptional levels. Using a splicing-defective allele of PASTICCINO2 (PAS2), a gene essential for plant development, we isolated suppressor mutations modifying pas2-1 mRNA profiles and restoring wild-type growth. Three suppressor of pas2 (sop) mutations modified the degradation of mis-spliced pas2-1 mRNA species, allowing the synthesis of a functional protein. Cloning of the suppressor mutations identified the core subunit of the exosome SOP2/RRP4, the exosome nucleoplasmic cofactor SOP3/HEN2 and a novel zinc-finger protein SOP1 that colocalizes with HEN2 in nucleoplasmic foci. The three SOP proteins counteract post-transcriptional (trans)gene silencing (PTGS), which suggests that they all act in RNA quality control. In addition, sop1 mutants accumulate some, but not all of the misprocessed mRNAs and other types of RNAs that are observed in exosome mutants. Taken together, our data show that SOP1 is a new component of nuclear RNA surveillance that is required for the degradation of a specific subset of nuclear exosome targets.
Highlights
The synthesis of mRNA in eukaryotes is a complex multistep process, involving the transcription of DNA into RNA, capping, splicing of intronic sequences and maturation of the 3’ end of the messenger prior to export to the cytoplasm for translation into protein
The very long chain fatty acids (VLCFA; 20 carbons and over) produced by the elongase complex are essential for plant growth as demonstrated by the loss of PAS2 in pas2 null mutants leading to embryo lethality [16]
Suppressor plants were screened from individual progeny of M1 plants at the seedling stage based on the restoration of cotyledon organogenesis of pas2-1Y (Fig 1A and S1A Fig)
Summary
The synthesis of mRNA in eukaryotes is a complex multistep process, involving the transcription of DNA into RNA, capping, splicing of intronic sequences and maturation of the 3’ end of the messenger prior to export to the cytoplasm for translation into protein. The exosome interacts with activator/adaptor complexes containing RNA helicases, RNA binding proteins or terminal nucleotidyl transferases that are required for exosome activity and are involved in substrate recognition. The composition of these activator/adaptor complexes varies between different intracellular compartments and between species. The nucleolar exosome complex interacts with the RNA helicase MTR4, the RNA binding protein ZCCHC7, and the terminal nucleotidyl transferase hTRF4 in a complex similar to yeast TRAMP complexes [9]. The human MTR4 is present in the nucleoplasm where it is associated with the RNA binding proteins ZCCHC8 and RBM7 to form the so-called (Nuclear EXosome Targeting complex) complex [10,11]. Targets promoter upstream transcripts, enhancer RNAs, 3’ extended small nucleolar RNAs (snoRNAs) and introns and is considered as a central activator/adaptor complex of exosomemediated RNA surveillance
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