| Prunus L.is an economically and ornamentally important genus,consisting of250–400 species of trees and shrubs widely distributed in the temperate Northern Hemisphere to subtropical and tropical regions.The Maddenia group of Prunus comprises four to seven species endemic to East Asia,which presents a disjunctive distribution from Himalayas to Wuyi Mountain in the eastern China.Due to limited sampling or low informativeness of molecular evidence used in previous studies,phylogenetic relationship of Prunus is unresolved,and the understanding of diversity process and key character evolution of Prunus is still limited.In addition,though revision has been done,species number and delimitation standard of Maddenia group are still unclear due to existence of intermediate morphological features,overlapped distribution and lacking of comprehensive molecular systematics analyses.In this study,we obtained nuclear specific-locus amplified fragment sequencing data and plastid genomes for 31 Prunus species and two outgroups.In addition,we used genome skimming to generate the DNA sequence data for 22 samples,including 17 Maddenia individuals and five outgroups.We reconstructed phylogeny of Prunus and Maddenia group based on plastomes,nuclear SNP and single-copy nuclear genes,respectively.We also estimated divergence time and reconstructed the ancestral state of Prunus.We conducted species delimitation of Maddenia group integrating the plastome,nuclear micromorphological and geographical distribution evidence.The results show that:1.A well-resolved phylogeny of Prunus supported three main clades,i.e.,the racemose group,the solitary-flower group and the corymbose group.The solitary-flower group and the corymbose group formed a clade and together they were both sister to the racemose group.2.Phylogenetic analyses inferred from different datasets indicated obvious cytonuclear discord within Prunus;Hy De results revealed pervasive hybridization within Prunus,especially in the racemose group.3.Prunus was inferred to have diversified initially around 67.86 Mya in the late Cretaceous,which was consistent with previous studies.The diversification of the three major clades began between Eocene to Miocene,corresponding to two climatic cooling events.3.The most recent common ancestor of the Prunus had a racemose inflorescence,and the solitary flower and corymb inflorescence types were derived with the reduction of the flower number and suppression of the rachis,respectively.4.Maddenia group contains five species,i.e.,Prunus fujianensis,P.himalayana,P.gongshanensis,P.hypoleuca,and P.hypoxantha.Our results supported that P.incisoserrata and P.wilsonii should be merged with P.hypoleuca and P.hypoxantha,respectively.P.fujianensis was a cryptic species.5.Hybridization events exist throughout Maddenia group,the gene flow frequently occurred between P.hypoleuca and P.hypoxantha,which seems to be “diverging” species.6.The phylogenetic trees based on eight concatenated hypervariable regions in plastome had a similar topology with the complete plastomes,showing their potential as molecular markers and effective barcodes for further population genetics and phylogeographic studies on Maddenia group.This study provides a stable phylogenetic framework for Prunus,which is beneficial to the genetic breeding of Prunus and provides reference for the study of inflorescence evolution of other plant lineage,shedding new light on comprehensive species delimitation of other puzzle species. |
