Comparative transcriptome provides strategy for phylogenetic analysis and SSR marker development in Chaenomeles

The genus Chaenomeles has long been considered as an important ornamental, herbal and cash plant and widely cultivated in East Asian. Traditional researches of Chaenomeles mainly focus on evolutionary relationships on phenotypic level. In this study, we conducted RNA-seq for 10 Chaenomeles germplasms supplemented with one related species Docynia delavayi ( D. delavay ) by Illumina HiSeq2500 platform. After de novo assemblies, we have generated unigenes for each germplasm with numbers from 40 084 to 48 487. By pairwise comparison of the orthologous sequences, 9 659 othologus within the 11 germplasms were obtained, with 6 154 othologous genes identified as single-copy genes. The phylogenetic tree was visualized to reveal evolutionary relationship for these 11 germplasms. GO and KEGG analyses were performed for these common single-copy genes to compare the functional similarities and differences. Selective pressure analysis based on 6 154 common single-copy genes reveals that 45 genes were under positive pressure selection. Most of them involved in plant disease defense system building process. 292 genes containing simple sequence repeats (SSRs) were used to develop SSR markers and compare their function in secondary metabolism pathways. Finally, 10 primers were chosen as SSR markers candidates for Chaenomeles germplasms by comprehensive screening. Our research provides new methodology and reference for future related research in Chaemomeles and is also useful for improvement, breeding and selection project in other related species.