Characterization of Two Complete Chloroplast Genomes in the Tribe Gnaphalieae (Asteraceae): Gene Loss or Pseudogenization of trnT-GGU and Implications for Phylogenetic Relationships

Abstract

The tribe Gnaphalieae is one of the largest and most complex in the Asteraceae family. The taxonomic delimitations of the tribe Gnaphalieae have been inferred by researchers; however, the exact relationships between it and other tribes remain in dispute, likely because of complicated evolutionary histories. To improve our understanding of this tribe, we investigated the complete chloroplast (cp) genomes of two Asian Gnaphalieae taxa, namely that within Anaphalissinica and Leontopodium leiolepis, and used this information to infer their phylogenetic relationships and evolution. The cp genomes of A. sinica and L. leiolepis were found to be 152,718 bp and 151,072 bp long, respectively, with gene contents and orders that resembled those of other Asteraceae species. However, we determined that the trnT-GGU genes within the two Gnaphalieae cp genomes were either pseudogenized or lost. Because these gene features have also been identified in other Gnaphalieae genera, but not among other Asteraceae species, they reinforce the taxonomic boundary of the tribe Gnaphalieae as an independent group. Moreover, based on the trnT-GGU gene features in members of the HAP clade, we speculate that the parental lineages of the genera Anaphalisand Pseudognaphalium have an allopolyploid origin. Thus, mutations in the trnT-GGU gene may be used in future studies as indicators of generic and/or tribal relationships. Using 52 protein-coding genes, we performed a phylogenetic analysis which further indicated that, alongside the tribes Astereae and Anthemideae, the tribe Gnaphalieae is a monophyletic taxon. We also identified 63 and 81 SSRs in L. leiolepis and A. sinica cp genomic sequences, respectively. The results described here will be useful for inferring the evolutionary history of the tribe Gnaphalieae, and specific genomic information can be applied in conservation strategies for endangered edelweiss ( Leontopodium R. Br. ex Cass.) and pearly everlasting ( AnaphalisDC.) species.