# The Complete Chloroplast Genome of Idesia polycarpa and Comparative Analysis of Related Species

## TL;DR

This study sequenced the chloroplast genome of the oil grape and compared it with related species to understand its genetic structure and evolutionary relationships.

## Contribution

The study provides the first complete chloroplast genome of I. polycarpa and identifies genes under selective pressure in related species.

## Key findings

- The chloroplast genome of I. polycarpa has a typical tetrad structure with 130 unique genes.
- Phylogenetic analysis shows strong relationships among I. polycarpa and other Salicaceae species.
- Genes like rpl16, ycf1, rps18, and rpl22 are under significant selective pressure in related species.

## Abstract

Background/Objectives: The oil grape (Idesia polycarpa), often called the “golden tree”, is an essential woody plant valued for its edible oil. Although its economic significance is recognized, the specifics of its chloroplast genome and evolutionary connections remain unclear. This study sequenced the chloroplast genome of I. polycarpa and performed a comparative analysis of its genome structure, genetic diversity, and phylogenetics using chloroplast data from related species. Methods: In this study, we sequenced and annotated the whole chloroplast genome of I. polycarpa via GISEQ-500 sequencing and de novo assembly. Results: The chloroplast genome of I. polycarpa exhibits a typical tetrad structure, with a length of 155,899 bp and a GC content of 36.78%. It comprises 130 unique genes, including 85 coding genes, 37 tRNAs, and eight rRNAs, showing notable conservation in gene composition and arrangement compared to closely related species. However, the inverted repeat region boundaries are narrower. Phylogenetic analysis showed strong relationships among I. polycarpa, Bennettiodendron brevipes, Poliothyrsis sinensis, Itoa orientalis, and Carrierea calycina within the Salicaceae family. Additionally, positive selection analysis revealed that rpl16, ycf1, rps18, and rpl22 are under significant selective pressure in related species, likely linked to adaptations for photosynthesis and environmental responses. Conclusions: This research provides vital molecular foundations for the conservation, classification, and enhancement of I. polycarpa germplasm resources, advancing the study of adaptive evolutionary mechanisms and broadening the genomic database for I. polycarpa.