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The Chinese elm is an important tree ecologically; however, little is known about its genetic diversity and adaptation mechanisms. In this study, a total of 107 individuals collected from seven natural populations in eastern China were investigated by specific locus amplified fragment sequencing (SLAF-seq). Based on the single nucleotide polymorphisms (SNPs) detected by SLAF-seq, genetic diversity and markers associated with climate variables were identified. All seven populations showed medium genetic diversity, with PIC values ranging from 0.2632 to 0.2761. AMOVA and Fst indicated that a low genetic differentiation existed among populations. Environmental association analyses with three climate variables (annual rainfall, annual average temperature, and altitude) resulted in, altogether, 43 and 30 putative adaptive loci by Bayenv2 and LFMM, respectively. Five adaptive genes were annotated, which were related to the functions of glycosylation, peroxisome synthesis, nucleic acid metabolism, energy metabolism, and signaling. This study was the first on the genetic diversity and local adaptation in Chinese elms, and the results will be helpful in future work on molecular breeding.

In this study, whole chloroplast genomes of five Salix species (S. argyracea, S. dasyclados, S. eriocephala, S. integra 'Hakuro Nishiki', and S. suchowensis) were sequenced. These chloroplast genomes were 155 ,605, 155, 763, 155, 552, 155, 538, and 155 ,550 bp in length, harboring 131 genes (77 unigenes), 37 tRNA genes, 8 rRNA genes, and 86 mRNA genes, respectively. The genes ycf1, psaI, ycf2-2, rpoC2, rpl22, atpF, and ndhF were under positive selection among the 21 Salix species. psaI, ycf2-2, atpF, and ycf1-2 were under positive selection between the tree willow and shrub willow, and rpoC2, rpl22, and ycf1-2 were positively selected among the shrub genomes. The gene rps7 was most variable among the genomes. Phylogenetic analysis of 21 Salix species and Chosenia arbutifolia provide evidence that the cp genome data partially support the relationship with traditional taxonomic concepts in the Flora of China. This chloroplast genome elucidates Salix taxonomy and provides evidence for evolutionary research.

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