Comparative plastome analysis of Arundinelleae (Poaceae, Panicoideae), with implications for phylogenetic relationships and plastome evolution

Background: Arundinelleae is a small tribe within the Poaceae (grass family) possessing a widespread distribution that includes Asia, the Americas, and Africa. Several species of Arundinelleae are used as natural forage, feed, and raw materials for paper. The tribe is taxonomically cumbersome due to a paucity of clear diagnostic morphological characters. There has been scant genetic and genomic research conducted for this group, and as a result the phylogenetic relationships and species boundaries within Arundinelleae are poorly understood.

Results: We compared and analyzed 11 plastomes of Arundinelleae, of which seven plastomes were newly sequenced. The plastomes range from 139,629 base pairs (bp) (Garnotia tenella) to 140,943 bp (Arundinella barbinodis), with a standard four-part structure. The average GC content was 38.39%, but varied in different regions of the plastome. In all, 110 genes were annotated, comprising 76 protein-coding genes, 30 tRNA genes, and four rRNA genes. Furthermore, 539 simple sequence repeats, 519 long repeats, and 10 hyper-variable regions were identified from the 11 plastomes of Arundinelleae. A phylogenetic reconstruction of Panicoideae based on 98 plastomes demonstrated the monophyly of Arundinella and Garnotia, but the circumscription of Arundinelleae remains unresolved.

Conclusion: Complete chloroplast genome sequences can improve phylogenetic resolution relative to single marker approaches, particularly within taxonomically challenging groups. All phylogenetic analyses strongly support the monophyly of Arundinella and Garnotia, respectively, but the monophylly of Arundinelleae was not well supported. The intergeneric phylogenetic relationships within Arundinelleae require clarification, indicating that more data is necessary to resolve generic boundaries and evaluate the monophyly of Arundinelleae. A comprehensive taxonomic revision for the tribe is necessary. In addition, the identified hyper-variable regions could function as molecular markers for clarifying phylogenetic relationships and potentially as barcoding markers for species identification in the future.