Title: The complete chloroplast genome of Onobrychis gaubae (Fabaceae-Papilionoideae): comparative analysis with related IR-lacking clade species

Abstract Plastid genome sequences provide valuable markers for surveying the evolutionary relationships and population genetics of plant species. In the present study, the complete plastid genome of Onobrychis gaubae, endemic to Iran, was sequenced using Illumina paired-end sequencing and was compared with previously known genomes of the IRLC species of legumes. The O. gaubae plastid genome was 123,645 bp in length and included a large single-copy (LSC) region of 81,034 bp, a small single-copy (SSC) region of 13,788 bp and one copy of the inverted repeat (IRb) of 28,823 bp. The genome encoded 110 genes, including 76 protein-coding genes, 30 transfer RNA (tRNA) genes and four ribosome RNA (rRNA) genes and possessed 89 simple sequence repeats (SSRs) and 28 repeated structures with the highest proportion in the LSC. Comparative analysis of the chloroplast genomes across IRLC revealed three hotspot genes (ycf1, ycf2, clpP) which could be used as molecular markers for resolving phylogenetic relationships and species identification. IRLC plastid genomes also showed multiple gene losses and inversions. Phylogenetic analyses revealed that O. gaubae is closely related to Hedysarum. The complete O. gaubae genome is a valuable resource for investigating evolution of Onobrychis species and can be used to identify related species.