Fig. 1

The numbers of PPR genes divided by species and subgroups and in the context of the phylogeny of plants. (a) Numbers and subclasses of PPR genes in moss, Selaginella, foxtail millet, Arabidopsis, rice. (b) Motif structures of PPR proteins. Schematic representation of typical plants PPR proteins from each subclass [7, 8, 10]. The number and even order of repeats can vary in individual proteins. The dashed line between the E and E+ motifs indicates that the E+ extension is not always present. (c) Phylogeny of plants. The species and the members of PPRs were labeled in end branch. Vascular plants appeared ~410 million years ago, then diverged into several lineages of which only two survive: the euphyllophytes (ferns and seed plants) and the lycophytes [25]