Evidence of inter-sectional chloroplast capture in Corymbia among sections Torellianae and Maculatae

Abstract

Chloroplast capture through hybridisation and introgression is well described within Eucalyptus. Despite the propensity of the Corymbia genus (eucalypts) to form hybrids from wide crosses, description of chloroplast capture in Corymbia has, until recently, been limited. In this study our aim was to investigate evidence of intersectional chloroplast capture between sections Torellianae and Maculatae. Using whole-genome next-generation sequencing data, the complete chloroplast genomes were assembled from four Corymbia taxa: Corymbia citriodora subspecies citriodora (Hook.) K.D.Hill & L.A.S.Johnson, Corymbia citriodora subspecies variegata (F.Muell.) A.R.Bean & M.W.McDonald, Corymbia henryi (S.T.Blake) K.D.Hill & L.A.S.Johnson, and Corymbia torelliana (F.Muell.) K.D.Hill & L.A.S.Johnson, represented by eight genotypes. Phylogenetic analysis and comparison among Corymbia chloroplast genomes and nuclear external transcribed spacer (ETS) sequences revealed chloroplast capture among Corymbia species across distinct sections Torellianae and Maculatae within subgenus Blakella. Reticulate evolution, along with Eucalyptus, likely extends into Corymbia as evidenced by incongruent plastid and nuclear phylogenetic trees, suggestive of its importance of hybridisation and introgression during the evolution of eucalypts.