Handeliodendron bodinieri (Lévl.) Rehd. and Eurycorymbus cavaleriei (Lévl.) Rehd. et Hand.-Mazz.(Sapindaceae) are endangered deciduous woody plants, which are endemic to China. The relationship between these two species and other members of Sapindaceae is not well resolved.

Historically, there were considerable controversies about the circumscription of Sapindaceae, predominantly the traditionally defined Aceraceae and Hippocastanaceae should be incorporated into Sapindaceae or separated. The concept of a broadly defined Sapindaceae was adopted by the newly published Angiosperm Phylogeny Group, which supported the merging of Aceraceae and Hippocastanaceae into Sapindaceae.

Researchers from the Wuhan Botanical Garden of the Chinese Academy of Sciences (CAS) sequenced and assembled the complete chloroplast (cp) genomes of H. bodinieri and E. cavaleriei.

According to the researchers, the cp genome sizes of H. bodinieri and E. cavaleriei were 151,271 and 158,690 bp, respectively. Their gene order, gene content and molecular structure were similar to that of cp genomes of other Sapindaceae species. Comparative analysis of complete cp genomes revealed that the cp genome size of the Hippocastanoideae was generally smaller across Sapindaceae, although this finding should be tested further with sufficient sampling.

Three highly divergent regions (Ycf1, ndhC-trnV-UAC, and rpl32-trnL-UAG-ccsA) could be used as the specific DNA barcodes within Sapindaceae. Inverted repeat regions of the H. bodinieri and E. cavaleriei cp genomes showed noticeable contraction and expansion, respectively. Phylogenetic results consistently confirmed that H. bodinieri had a close relationship with the genus Aesculus, strongly supported E. cavaleriei as sister to Dodonaea viscosa.

This study strongly supports that the subdivision of four subfamilies within Sapindaceae and Handeliodendron is not nested within the genus Aesculus. As the national-level protected species, both H. bodinieri and E. cavaleriei attract scientific attention in many aspects, and this work will provide valuable chloroplast genomic information, and contribute to facilitating future studies in population genetics and conservation biology.

The research was published in BMC Genomics and it was supported by grants from the National Science & Technology Fundamental Resources Investigation Program of China, the National Natural Science Foundation of China, and the Sino-Africa Joint Research Center of CAS.

Circular gene map of chloroplast genomes of Handeliodendron bodinieri and Eurycorymbus cavaleriei. (Image by YANG Jiaxin)