Compatibility with Killer Explains the Rise of RNAi-Deficient Fungi

摘要

RNA interference (RNAi), lost in a recent ancestor of Sacchammyces cerevisiae (fig. S1), can be restored by introducing Argonaute (AG01) and Dicer (DCR1) from a close relative, Sacchammyces castellii (1). The reconstituted pathway silences endogenous transposons, which explains retention of RNAi in some lineages (1). But why is it lost in others? To address this question, we determined the consequences of restoring RNAi to S. cerevisiae. Restoration of RNAi had little if any effect on growth measured under 50 different conditions, and high-throughput RNA sequencing (RNA-Seq) results indicated minimal changes in nonrepeu'tive mRNA accumulation (figs. S2 to S6 and tables S1 and S2). However, restoring RNAi to S. cerevisiae profoundly affected maintenance of killer, an endemic viral system cytoplasmatically inherited as a double-stranded RNA (dsRNA) virus, L-A, and its satellite dsRNA, M (2).