Variation Of Chroloplast Genomes In Acer Griseum And Its Phylogenetic Relationship With Related Species

Acer griseum belongs to the Sapindaceae family,a deciduous tree,which is up to 20 m.It is an endemic and endangered species in China,and it is also a rare colored-trunk tree in the garden.It mainly distributes in Central China.The habitat status of the natural population was researched.Through sequencing chloroplast genome of A.griseum and its related species and drawing chloroplast gene map,the difference analysis and phylogenetic analysis was carried out.In order to provide theoretical basis for the protection strategies of A.griseum,the diversity of chloroplast haplotype,the genetic structure and population evolution were analyzed through chloroplast genome sequencing of more A.griseum taxon from different populations.The main results are as the followings:(1)So far,totaling 469 trees of 21 natural populations of A.griseum in 7 provinces and 1municipality have been surveyed,and all molecular samples have been collected.The DBH of the A.griseum is mainly distributed between 8.0 to 15.9 cm,about 45.6%.There are 6 strains with a DBH of 40.0 cm or more,and the single plant with the largest DBH is from the Chongqing Chengkou population of Daba Mountain,which is 45.1 cm.Most of the ground diameters are distributed between 32.0 to 43.9 cm,and the maximum ground diameter is 63 cm.That located in Laojun forest Mountain,Luanchuan,Henan.(2)6 complete cp DNA sequences were obtained,three of which were A.griseum,and the other were A.nikoense,A.triflorum,A.cissifolium.The chloroplast gene map was drawn.The chloroplast genome of Acer was a typical circular structure with a length of about 156 kb.The chloroplast genome consists of four typical parts.The composition,order and direction of the genes were consistent,and 136 genes were encoded.The cp DNA differences of A.griseum between the populations were very small,and the species of different Acer are relatively conservative.There was no phenomenon of gene rearrangement and deletion mutation.There was a high evolution in the pseudogene ycf1.About 80 SSR loci in different Acer were found,and most of repeat were single-nucleotide.The phylogenetic tree based on cp DNA was composed of three high-supporting evolutionary branches.The first branch contains only one species of A.buergerianum;The second branch includes four species: A.griseum,A.triflorum,A.nikoense and A.cissifolium,all of which are trifoliolate.The third branch includes four species:A.davidii,A.morrisonense,A.miaotaiense,A.truncatum.Consistented with Morphology-based classification.(3)The chloroplast genome of 26 individuals from 21 natural populations were sequenced,and 21 haplotypes were obtained,almost one haplotype per population.The length of the comparison sequence was 156 kb.A total of 62 polymorphic loci were detected.The total haplotype polymorphism(Hd)was 0.982,and the nucleotide polymorphism(π)was 0.0016.Neutral testing and mismatch analysis indicated that the population of A.griseum has experienced an expansion event in history.The co-progenitor time of the different A.griseum populations calculated by molecular clock is about 2.86 MYA,probably belonging to the late Pleistocene.It is speculated that the origin of A.griseum at least before the forth glacier.The same as some rare and endangered species originating from the subtropical region,A.griseum survived in the subtropical region which not directly covered by glaciers.Then the glaciers expanded to the north.A.griseum was difficult to be naturally renewed.In some areas,there were some traces of damage,and a protected area or the artificial breeding base can be established to protect A.griseum.It is recommended to use Shennongjia as a priority protection unit,while Xichuan and Neixiang areas in Henan are used as breeding bases for A.griseum.