The Pentatricopeptide Repeat (PPR) gene family produces RNA-binding proteins that target organellar transcripts. The PPR family is expanded in land plants, with nearly 450 genes identified in Arabidopsis thaliana. In plants with a Cytoplasmic Male Sterility (CMS) phenotype, members of the PPR family can act as a RESTORER OF FERTILITY (Rf) and are part of a subset of genes called RESTORER OF FERTILITY-LIKE (RFL). Unlike other PPR transcripts, RFL transcripts are targets of both microRNA (miRNA) and trans-acting siRNA (tasiRNA) and produce secondary siRNA after initial miRNA- or tasiRNA-guided cleavage. We utilized the A. lyrata genome assembly and high-throughput sequencing of small RNA to examine the evolutionary dynamics of the PPR gene family and the pattern of small RNA targeting of RFL transcripts. We found an expanded set of 539 PPR genes in A. lyrata, 51 of which were in the RFL group, often in multiple collinear copies when compared to their A. thaliana orthologs. In-species RFL paralogs appear to be more related to one another than to their collinear orthologs, which is possible evidence of gene conversion or ectopic recombination. miRNA targeting of RFL transcripts is largely conserved with nearly two-thirds of all target sites maintained. TasiRNA targeting was less conserved with roughly one-third of comparable validated tasiRNA targets maintained in both species. However, when clusters of potential tasiRNA targets were considered, roughly two-thirds of target sites are conserved. Production of secondary siRNA from A. lyrata PPR transcripts is less well defined than in A. thaliana, with strong signals coming from phases that are not concordant with the miRNA- or tasiRNA-guided cleavage sites. / Graduation date: 2013