The Pentatricopeptide Repeat Gene Family in Salvia miltiorrhiza: Genome-Wide Characterization and Expression Analysis

The pentatricopeptide repeat (PPR) gene family is one of the largest gene families in plants and plays important roles in posttranscriptional regulation. In this study, we combined whole genome sequencing and transcriptomes to systematically investigate PPRs in Salvia miltiorrhiza, which is a well-known material of traditional Chinese medicine and an emerging model system for medicinal plant studies. Among 562 identified SmPPRs, 299 belong to the P subfamily while the others belong to the PLS subfamily. The majority of SmPPRs have only one exon and are localized in the mitochondrion or chloroplast. As many as 546 SmPPRs were expressed in at least one tissue and exhibited differential expression patterns, which indicates they likely play a variety of functions in S. miltiorrhiza. Up to 349 SmPPRs were salicylic acid-responsive and 183 SmPPRs were yeast extract and Ag+-responsive, which indicates these genes might be involved in S. miltiorrhiza defense stresses and secondary metabolism. Furthermore, 23 salicylic acid-responsive SmPPRs were co-expressed with phenolic acid biosynthetic enzyme genes only while 16 yeast extract and Ag+-responsive SmPPRs were co-expressed with tanshinone biosynthetic enzyme genes only. Two SmPPRs were co-expressed with both phenolic acid and tanshinone biosynthetic enzyme genes. The results provide a useful platform for further investigating the roles of PPRs in S. miltiorrhiza.