Molecular Evidence For The Homoploid Hybrid Origin Of Hi Ppophae Litangensis (Elaeagnaceae)

The genus Hippophae belonging to the Elaeagnaceae,contains seven species and ten subspecies based on the classification in Bartish et al.,H.goniocarpa and H.litangensis have been inferred as the homoploid hybrid species.Previous studies using maternally inherited chloroplast DNA(cpDNA)demonstrated that H.goniocarpa was double maternal origin of diploid hybrid specie through hybridization between H.rhamnoides subsp.sinensis and H.neurocarpa subsp neurocarp,while the origin of H.litangensis remain to be a controversy.Here,we testified the hybrid speciation of H.litangensis using the maternally inherited trnL-trnF fragment,biparentally inherited ITS fragments and SSRs.The main conclusions were as follows:(1)Development of SSR primersA total of 6163 and 3527 SSRs(simple sequence repeats)motifs were identified via transcriptome and genomic surveying.Dinucleotide repeats were the most dominant types,while the trinucleotide repeats of EST-SSR(transcriptome SSR)were more frequent than that of gSSR(genomic-SSR).40 pairs of polymorphic primers of EST-SSR and 23 pairs of polymorphic primers were developed successfully.(2)Hybrid origin of H.litangensisBased on trnL-trnF haplotype and phylogeny analysis,H.litangensis and H.rhamnoides subsp.yunnanensis in sympatric region clustered in the same clade and shared haplotypes which supported the hypotheses of H.rhamnoides subsp.yunnanensis as a maternal parent.In the ITS haplotype network and phylogeny tree,part of H.litangensis and H.neurocarpa clustered in the same clade,H.litangensis and H.rhamnoides subsp.yunnanensis in sympatric region clustered in the same clade,the results supported H.neurocarpa as a male parent.Further STRUCTURE clustering analyses based on 15 SSR loci indicated that H.litangensis was originated from a directional hybridization between H.rhamnoides subsp.yunnanensis and H.neurocarpa,and thus different from H.goniocarpa,which originated from bidirectional hybridization between H.rhamnoides subsp.sinensis and H.neurocarpa.(3)Phylogeny based on a large data set of SSR loci using neighbour-joining method,showed that H.litangensis was seperated from other species,this was consistent with analyses based on trnL-trnF and ITS.Therefore,we considered that H.litangensis could be considered as a different species rather than a subspecies of H.goniocarpa.