ERIL1, the plant homologue of ERI‐1, is involved in the processing of chloroplastic rRNAs

Abstract

Proteins belonging to the enhancer of RNA interference-1 subfamily of 3'-5' exoribonucleases participate in divergent RNA pathways. They degrade small interfering RNAs (siRNAs), thus suppressing RNA interference, and are involved in the maturation of ribosomal RNAs and the degradation of histone messenger RNAs (mRNAs). Here, we report evidence for the role of the plant homologue of these proteins, which we termed ENHANCED RNA INTERFERENCE-1-LIKE-1 (ERIL1), in chloroplast function. In vitro assays with AtERIL1 proved that the conserved 3'-5' exonuclease activity is shared among all homologues studied. Confocal microscopy revealed that ERL1, a nucleus-encoded protein, is targeted to the chloroplast. To gain insight into its role in plants, we used Nicotiana benthamiana and Arabidopsis thaliana plants that constitutively overexpress or suppress ERIL1. In the mutant lines of both species we observed malfunctions in photosynthetic ability. Molecular analysis showed that ERIL1 participates in the processing of chloroplastic ribosomal RNAs (rRNAs). Lastly, our results suggest that the missexpression of ERIL1 may have an indirect effect on the microRNA (miRNA) pathway. Altogether our data point to an additional piece of the puzzle in the complex RNA metabolism of chloroplasts.

Organellar and Secretory Ribonucleases: Major Players in Plant RNA Homeostasis

“…Recombinant ERIL1 possess a 39-59 exoribonuclease activity on single-stranded but not doublestranded RNA in vitro. The mutants showed incorrect processing of the 23S to 4.5S rRNA precursor and a decrease in mature 4.5S and 5S rRNA, but the exact molecular defects remain unclear (Mermigka et al, 2016).…”

Snipper, an Eri1 homologue, affects histone mRNA abundance and is crucial for normal Drosophila melanogaster development

“…Deletion mutants of the SAP domain are still functional [5,6] in humans and mice, whereas plant [7] and Drosophila ERI1 homologues lack it completely. The single ERI1 homologue in Drosophila melanogaster Snipper (Snp) is a 3 0 -5 0 exonuclease, but its in vivo function remains elusive.…”

“…

Edited by Didier Stainier

The conserved 3 0 -5 0 RNA exonuclease ERI1 is implicated in RNA interference inhibition, 5.8S rRNA maturation and histone mRNA maturation and turnover. An ERI1 has also been identified in plants where, although the 3 0 Exo activity is conserved, its function seems to differ from that of the nonplant ERI1s characterized to date [7].Discovered in a genetic screen in Caenorabditis elegans for enhanced RNAi in neurons [8], ERI1 affects small regulatory RNA abundance in different organisms. Here, we report Snp requirement for normal Drosophila development, since its perturbation leads to larval arrest and tissue-specific downregulation results in abnormal tissue development.

…”

“…Although the SAP domain is known to facilitate DNA binding [4], its function in ERI1 is still unknown. Deletion mutants of the SAP domain are still functional [5,6] in humans and mice, whereas plant [7] and Drosophila ERI1 homologues lack it completely. An ERI1 has also been identified in plants where, although the 3 0 Exo activity is conserved, its function seems to differ from that of the nonplant ERI1s characterized to date [7].Discovered in a genetic screen in Caenorabditis elegans for enhanced RNAi in neurons [8], ERI1 affects small regulatory RNA abundance in different organisms.…”

“…Deletion mutants of the SAP domain are still functional [5,6] in humans and mice, whereas plant [7] and Drosophila ERI1 homologues lack it completely. An ERI1 has also been identified in plants where, although the 3 0 Exo activity is conserved, its function seems to differ from that of the nonplant ERI1s characterized to date [7].Discovered in a genetic screen in Caenorabditis elegans for enhanced RNAi in neurons [8], ERI1 affects small regulatory RNA abundance in different organisms. Eri1 mutants in C. elegans and cell lines from H. sapiens and Mus musculus display elevated siRNA levels and increased suppression of target genes [8][9][10].…”