Comparative analysis of chloroplast genomes of Sanguisorba species and insights into phylogenetic implications and molecular dating

Sanguisorba is a small genus, which consists of about 15 species widely
distributed in North America and Eurasia. Previous studies on Sanguisorba
are useful for understanding of phylogeny and chloroplast (cp) genome
evolution of Sanguisorba. However, the cp genome resources of Sanguisorba
are still limited, and the phylogeny and molecular dating for Sanguisorba
and its relatives still need further explored. Here, we reported four cp
genomes of Sanguisorba and conducted comparative analysis of the four
Sanguisorba cp genomes plus five previously published ones. The nine cp
genomes of Sanguisorba have typical tetrad quadripartite structure, with a
total length of 154 282 to 155 730 bp, and their gene content, gene
structure, and gene order are relatively conservative. The analysis of
single copy (SC)/inverted repeat (IR) boundaries shows very slight
boundary differences in Sanguisorba cp genomes. Eight variation hotspots
were screened as excellent candidate markers of Sanguisorba. Phylogenetic
analysis indicated Sanguisorba was monophyletic and was a member of tribe
Agrimonieae subtribe Sanguisorbinae. Within Sanguisorba, S. filiformis is
a sister group of six other taxa in the present sampling. Estimation of
the divergence times indicated that subtribes Agrimoniinae and
Sanguisorbinae diverged at the transition between the Oligocene and the
Miocene, and divergent times of Agrimonieae genera ranged from the late
Miocene to the Middle Pleistocene. This study enriches the available cp
genome resources of Sanguisorba, and it is of great significance to
further study the phylogeny and evolution of Sanguisorba and its
relatives.