Plastid DNA sequencing and nuclear SNP genotyping help resolve the puzzle of central American Platanus

Background and aims = Recent research on the history of Platanus reveals that hybridisation phenomena occurred in the central American species. This study has two goals: to help resolve the evolutive puzzle of central American Platanus, and to test the potential of real-time PCR for detecting ancient hybridisation. Methods = We used both sequencing of a uniparental cpDNA marker (psbA-trnH(GUG) intergenic spacer) and qualitative and quantitative SNP genotyping of biparental nrDNA markers [LEAFY intron 2 (LFY-i2) and internal transcribed spacer 2 (ITS2)]. Key Results = Based on the SNP genotyping results, several Platanus accessions show the presence of hybridisation/introgression including some accessions of P. rzedowskii and of P. mexicana var. interior, and one of P. mexicana var. mexicana from Oaxaca (= P. oaxacana). Based on haplotype analyses of the psbA-trnH spacer, five haplotypes were detected. The most common of these is present in taxa belonging to P. orientalis, P. racemosa s.l., some accessions of P. occidentalis s.str. from Texas, P. occidentalis var. palmeri, P. mexicana s.str. and P. rzedowskii. This is highly relevant to genetic relationships with the haplotypes present in P. occidentalis s.str. and P. mexicana var. interior. Conclusions = Hybridisation and introgression events between lineages ancestral to modern central and eastern North American Platanus species occurred. Chloroplast haplotypes and qualitative and quantitative SNP genotyping provide information critical for understanding the complex history of Mexican Platanus. Compared to the usual molecular techniques of subcloning, sequencing and genotyping, real-time PCR assay is a very quick and sensitive technique for analysing complex evolutionary patterns.