| Juglans is a member of the Juglandaceae,with about 21-23 species.It is a relatively evolved genus within the genus Juglans.The genus Juglans is widely distributed in the world,with intermittent plant communities in Europe,Asia and the Americas.Dode,the earliest scientist to study the taxonomy of the genus Juglans,who divided the genus Juglans according to the leaf and flower morphology into Sect.Rhysocaryon,Sect.Cardiocaryon,and Sect.Trachycaryon)and walnut group(Sect.Dioscaryon or Sect.Juglans)(Dode L A.1909a;Dode L A.1909b).Manning(1978)found the same result according to the characteristics of fruits(Manning W E.1978).In walnut group,most research about J.regia,few about J.sigillata.In order to clarify whether there is a genetic relationship between them,we carried out the development of the transcriptome SSRs locus in Juglans sigillata Dode,which was followed by the same genetic markers for homology distribution of walnut and walnut Gene flow analysis.In addition,based on the research status of Juglans regia,we conducted a lineage phytogeographic research on the whole range of walnut populations in China,including the use of EST-SSRs universal primers developed by the team from several other species and the chloroplast genome of 17 individuals.The sequence studied the population genetic structure and dynamic history of walnut in China.Our research provided favorable scientific evidence for the follow-up identification and development of walnut plant germplasm resources.Through study and research of chloroplast genome and transcriptome on iron walnut and phylogeography on common walnut detected the following conclusions:(1)The chloroplast genome consisted of a large single copy(LCS)of 89,872 bp,an inverted region(IR)of 52,072 bp,and a short single copy(SSC)of 18,406 bp.The chloroplast genome consisted of 137 annotated genes,with 71 unique coding regions and eight coding regions that were repeated in the inverted region.De novo assembly of the transcriptome yielded 83,112 unigenes with an average length of 686.9 bp.A search against the Gene Ontology(GO)database identified 19,718 unigenes.We evaluated transcriptome-derived microsatellite markers and chloroplast sequence polymorphisms in 48 J.sigillata individuals from three populations and 66 individuals from five other Chinese walnut(Juglans)species.We found 20 EST-SSRs and 7 loci in the chloroplast that were polymorphic and easily amplified.The number of alleles per locus ranged from 3 to 10.The markers we developed will also lay the foundation for the follow-up genetic research of iron walnut lineage and its genetic relationship with the same species of walnut.(2)As an important economic species,the genetic structure of walnut is affected by many factors.In this study,we estimated the genetic diversity and spatial genetic structure of 31 walnut populations sampled across its Chinese range using 23 microsatellite markers.At the same time,we reconstructed the dynamic history of walnut and the distribution range of ancient times by combining genetic data with distributional model(SDM).The genetic data indicated the presence of J.regia in glacial refugia in the Xingjiang province,Easter China,Qinling and Baishan Mountains,and Southwestern China.We conclude that the two distinct lineages divergence with others occurred about 2.79 Mya,while Southwestern China and Qinling and Baishan Mountains lineages were divergence the Quaternary glaciations(about 1.13 Mya).Remnants of these once-distinct genetic clusters of J.regia may warrant ecological management if they are to be retained as in situ resources.A population size expansion in northeastern China was detected in the last five centuries.The actual distribution of walnut in China resulted from the combined effects of expansion/contraction from multiple refugia after the Last Glacial Maximum and its human exploitation. |
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