ERIL 1, the plant homologue of ERI ‐1, is involved in the processing of chloroplastic rRNA s

Summary Proteins belonging to the enhancer of RNA interference‐1 subfamily of 3′–5′ exoribonucleases participate in divergent RNA pathways. They degrade small interfering RNA s (si RNA s), thus suppressing RNA interference, and are involved in the maturation of ribosomal RNA s and the degradation of histone messenger RNA s ( mRNA s). Here, we report evidence for the role of the plant homologue of these proteins, which we termed ENHANCED RNA INTERFERENCE ‐1‐ LIKE ‐1 ( ERIL 1), in chloroplast function. In vitro assays with At ERIL 1 proved that the conserved 3′–5′ exonuclease activity is shared among all homologues studied. Confocal microscopy revealed that ERL 1, 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 ERIL 1. In the mutant lines of both species we observed malfunctions in photosynthetic ability. Molecular analysis showed that ERIL 1 participates in the processing of chloroplastic ribosomal RNA s ( rRNA s). Lastly, our results suggest that the missexpression of ERIL 1 may have an indirect effect on the micro RNA (mi RNA ) pathway. Altogether our data point to an additional piece of the puzzle in the complex RNA metabolism of chloroplasts.