Phylogeny And The Evolution Of Inflorescences And Floral Organs In Prunus S.l.(Rosaceae)

Flowers and inflorescences have important taxonomic value and their developmental process provides abundant information for systematics and evolution.Prunus s.l.(Rosaceae)is an economically important source of various fruits and ornamentals.Our preliminary investigations demonstrated that Prunus varies with respects to inflorescence types and floral organs.Unfortunately,their development and evolution are still unclear.At the same time,the phylogenetic relationships in Prunus remain unresolved,because previous studies used only few molecular markers or few samples.In this project,we reconstruct a robust phylogeny of Prunus using 29 representative species and outgroups from chloroplast genome sequences obtained by next-generation sequencing and 11 sequences in the NCBI library.We investigate the formation and development of the inflorescences and floral organs of 8 species using scanning electron microscope.Lastly,we reconstruct the ancestral states of flower and inflorescence characters based on the phylogenetic hypothesis.The results show that:1.Prunus forms a monolog,and the monotropism of single-flower group,umbel group(except Prunus tomentosa)and racemes group are strongly supported.P.tomentosa and P.triloba(Amygdalus)are sister groups.Maddenia and Pygeum constitute mononoses,while Padus and Laurocerasus do not constitute mononoses.Maddenia is nested in Padus,while Pygeum is nested in Laurocerasus.2.Inflorescences show continuous variation from racemes to single flower in Prunus.Racemes and many flowers are ancestral traits.The general direction of evolution is that the axis of inflorescence is shortened and the number of flowering is reduced.3.The flower developmental and morphological data support that the perianth segments are differentiated in Maddenia and Pygeum,and the petals and sepals are tend to look similar in maturity stage.4.The number and position of stamens show high diversity in Prunus.The number and location of the first stamen whorl in different subgenera are the same.The number of stamen whorl in racemes was basically the same,and 3 is relatively primitive.In Cerasus,the number of stamen whorl increased to 6,while 6 stamen whorls are retained in the single-flower group.In Prunus s.s.,4 stamen whorls is probably secondary.Variations in stamen position may result from the degeneration or deletion of the preceding stamens.5.The developmental morphological characteristics of ovule have important taxonomic value.The ovules of Prunus are all anatropous double ovules.The diversity of ovules inraceme group is very high,and stable characters such as single integument and long appendages are found in Cerasus.In single-flower group,double integuments are found,and the pores are formed by inner integuments.Our work will not only help to resolve remaining questions regarding the phylogenetic relationships in Prunus,but also provide fundamental new insights in the evolution of reproductive system in the genus.Apart from these basic research results,our work will have applications in plant breeding of horticultural varieties and wild resource protection of Prunus.