RNA degradation, together with RNA synthesis, controls the steady-state level of viral RNAs in infected cells. The endoribonucleolytic cleavage of viral RNA is important not only for viral RNA degradation but for RNA recombination as well, due to the participation of some RNA degradation products in the RNA recombination process. To identify host endoribonucleases involved in degradation of Tomato bushy stunt virus (TBSV) in a Saccharomyces cerevisiae model host, we tested eight known endoribonucleases. Here we report that downregulation of SNM1, encoding a component of the RNase MRP, and a temperature-sensitive mutation in the NME1 gene, coding for the RNA component of RNase MRP, lead to reduced production of the endoribonucleolytically cleaved TBSV RNA in yeast. We also show that the highly purified yeast RNase MRP cleaves the TBSV RNA in vitro, resulting in TBSV RNA degradation products similar in size to those observed in yeast cells. Knocking down the NME1 homolog in Nicotiana benthamiana also led to decreased production of the cleaved TBSV RNA, suggesting that in plants, RNase MRP is involved in TBSV RNA degradation. Altogether, this work suggests a role for the host endoribonuclease RNase MRP in viral RNA degradation and recombination.Many RNA viruses evolve rapidly due to a high frequency of mutations and genetic recombination as well as reassortment of genomic components (1, 52). Comparison of viral RNA genomes has revealed that recombination has shaped the evolution of many RNA viruses (52). RNA recombination is the process that joins two or more noncontiguous segments of the same RNA or two separate RNAs together (32). Recombination events can have small or dramatic effects on viral genomes by introducing insertions or duplications, combining new sequences, or leading to deletions or rearrangements. RNA recombination also functions to repair truncated or damaged viral RNA molecules (16,17,30,37). The repair function of RNA recombination might compensate viruses for their high mutation rate, which could introduce detrimental mutations into the viral genomes and thus reduce the fitness of viral populations (38, 39). Therefore, depending on the nature of recombining RNAs, the locations of the recombinant junction sites, and the outcome of the recombination events, RNA recombination can guard the infectivity of the viral genome or can increase genome variability. Altogether, RNA recombination is a probabilistic event that can affect the population of viruses, contribute to virus variability, and function in genome repair that maintains the infectivity of RNA viruses (32, 39).In addition to the roles of the viral replicase and the viral RNA (31, 32), host proteins are likely involved in viral RNA recombination as well. Accordingly, recent genome-wide approaches with Tomato bushy stunt virus (TBSV), a tombusvirus infecting plants, and with the model host Saccharomyces cerevisiae have led to the identification of more than 30 host genes affecting viral RNA recombination (20,21,27,45,46). Detailed analysis of...