Chloroplast Genomes and Comparative Analyses among Thirteen Taxa within Myrsinaceae s.str. Clade (Myrsinoideae, Primulaceae)

The Myrsinaceae s.str. clade is a tropical woody representative in Myrsinoideae of Primulaceae and has ca. 1300 species. The generic limits and alignments of this clade are unclear due to the limited number of genetic markers and/or taxon samplings in previous studies. Here, the chloroplast (cp) genomes of 13 taxa within the Myrsinaceae s.str. clade are sequenced and characterized. These cp genomes are typical quadripartite circle molecules and are highly conserved in size and gene content. Three pseudogenes are identified, of which ycf15 is totally absent from five taxa. Noncoding and large single copy region (LSC) exhibit higher levels of nucleotide diversity (Pi) than other regions. A total of ten hotspot fragments and 796 chloroplast simple sequence repeats (SSR) loci are found across all cp genomes. The results of phylogenetic analysis support the notion that the monophyletic Myrsinaceae s.str. clade has two subclades. Non-synonymous substitution rates (d(N)) are higher in housekeeping (HK) genes than photosynthetic (PS) genes, but both groups have a nearly identical synonymous substitution rate (d(S)). The results indicate that the PS genes are under stronger functional constraints compared with the HK genes. Overall, the study provides hypervariable molecular markers for phylogenetic reconstruction and contributes to a better understanding of plastid gene evolution in Myrsinaceae s.str. clade.