Study On Genetic Diversity And Chloroplast Genome Of Magnolia Shiluensis

Magnolia shiluensis（Chun&Y.F.Wu）Figlar is an evergreen tree belonging to Michelia genus（Magnoliaece）,which is mainly distributed in Hainan and Guangdong provinces of China.It has extremely high ornamental and wood use value,which is suitable for garden landscape and furniture industry.Due to the narrow distribution range,interference of human activities,natural disasters,low natural reproduction capacity,the wild population of M.shiluensis were faced fragmentation and sharp decline.Thus,it was listed as an endangered species by International Union for Conservation of Nature.In this study,nSSR and cpDNA markers were used to study the genetic diversity and population structure of the currently preserved M.shiluensis,and to assemble its chloroplast genome to compare with related species.This research provides the theoretical basis to conservation and phylogenic analysis of M.shiluensis.The findings are as follows:1.High genetic diversity were detected in the populations of M.shiluensis.The average Na,Ne,I,Ho,and He of the population based on nSSR markers were 5.559,4.078,1.452,0.647,and 0.697,respectively.The population size were significantly related to Na,Ne,I,and Np,but not to Ho and He.Based on cpDNA markers,the length of the two gene spacer fragments is 1142 bp,with a total of 12 polymorphic sites,resulting in a total of 6 haplotypes.The nucleotide polymorphism and haplotype diversity are 0.00217 and 0.668,respectively.2.Moderate genetic differentiation were detected in the populations of M.shiluensis.The average F_ST,F_IS,F_IT,Nm was 0.162,0.071,0.217,and 1.447,based on nSSR markers.The genetic variation between populations based on cpDNA markers was 76.86%and within the population was 23.14%.Mental test correlation was inconsistent for both markers.3.The genetic structure of M.Shiluensis is obvious.Structure divided 6 populations into two clusters,separating most individuals in DL and the remaining 5 populations;PCoA results showed that individual plants except DL had different degrees of overlap;The results show that DL and YC are in the same branch,and the remaining groups are in another branch.DL population and YG population have more haplotypes than other populations.The haplotype H3 is located in the center of the network graph and is distributed in all populations,which may be an ancestral haplotype.4.M.shiluensis chloroplast genome structure and sequence are conserved.It has a typical quarter structure,with a total length of 160,075 bp,and LSC,SSC,and IR lengths of88,105 bp,18,796 bp,and 26,587 bp,respectively.The genome contains 131 genes,including86 protein-coding genes,37 tRNA genes,and 8 rRNA genes.Comparative analysis shows that the chloroplast genome of M.shiluensis is highly similar to its related species,and phylogenetic analysis shows that the relationship between M.shiluensis and Magnolia odora is closest.