Differences in the Functional Traits of Populus pruinosa Leaves in Different Developmental Stages.

Populus pruinosa Schrenk has the biological characteristics of heteromorphic leaves and is a pioneer species for wind prevention and sand fixation. The functions of heteromorphic leaves at different developmental stages and canopy heights of P. pruinosa are unclear. To clarify how developmental stages and canopy height affect the functional characteristics of leaves, this study evaluated the morphological anatomical structures and the physiological indicators of leaves at 2, 4, 6, 8, 10, and 12 m. The relationships of functional traits to the developmental stages and canopy heights of leaves were also analyzed. The results showed that blade length (BL), blade width (BW), leaf area (LA), leaf dry weight (LDW), leaf thickness (LT), palisade tissue thickness (PT), net photosynthetic rate (Pn), stomatal conductance (Gs), proline (Pro), and malondialdehyde (MDA) content increased with progressing developmental stages. BL, BW, LA, leaf dry weight, LT, PT, Pn, Gs, Pro, and the contents of MDA, indoleacetic acid, and zeatin riboside had significant positive correlations with canopy heights of leaves and their developmental stages. The morphological structures and physiological characteristics of P. pruinosa leaves showed more evident xeric structural characteristics and higher photosynthetic capacity with increasing canopy height and progressive developmental stages. Resource utilization efficiency and the defense ability against environmental stresses were improved through mutual regulation of each functional trait.

Phylogeography Reveals Geographic and Environmental Factors Driving Genetic Differentiation of Populus sect. Turanga in Northwest China.

Populus sect. Turanga (hereafter referred to as "Populus"), including Populus euphratica and Populus pruinosa, are the predominant tree species in desert riparian forests in northwestern China. These trees play key roles in maintaining ecosystem balance, curbing desertification, and protecting biodiversity. However, the distribution area of Populus forests has been severely diminished and degraded in recent years due to increased habitat destruction and human activity. Understanding the genetic diversity among Populus individuals and populations is essential for designing conservation strategies, but comprehensive studies of their genetic diversity in northwest China are lacking. Here, we assessed the population structures and genetic diversity of 1,620 samples from 85 natural populations of Populus (59 P. euphratica and 26 P. pruinosa populations) covering all of northwestern China using 120 single nucleotide polymorphism (SNP) markers. Analysis of population structure revealed significant differentiation between these two sister species and indicated that strong geographical distribution patterns, a geographical barrier, and environmental heterogeneity shaped the extant genetic patterns of Populus. Both P. euphratica and P. pruinosa populations in southern Xinjiang had higher genetic diversity than populations in other clades, perhaps contributing to local geographic structure and strong gene flow. Analysis of molecular variance (AMOVA) identified 15% variance among and 85% variance within subpopulations. Mantel tests suggested that the genetic variation among P. euphratica and P. pruinosa populations could be explained by both geographical and environmental distance. The genetic diversity of P. euphratica showed a significant negative correlation with latitude and longitude and a positive correlation with various environmental factors, such as precipitation of warmest quarter and driest month, temperature seasonality, and annual mean temperature. These findings provide insights into how the genetic differentiation of endangered Populus species was driven by geographical and environmental factors, which should be helpful for designing strategies to protect these genetic resources in the future.

Complete chloroplast genome sequence of Populus pruinosa Schrenk from PacBio Sequel II Platform.

Populus pruinosa Schrenk plays an important role on ecological services in desert areas. The complete chloroplast genome was reported in this study using the PacBio Sequel II Platform. The chloroplast genome with a total size of 157,856 bp consists of two inverted repeats (IR, 27,673 bp) separated by a large single-copy region (LSC, 85,867 bp) and a small single-copy region (SSC, 16,645 bp). Further annotation revealed the chloroplast genome contains 111 genes, including 78 protein-coding genes, 29 tRNA genes, and 4 rRNA genes. A total of 151 simple sequence repeats (SSRs) were identified in the chloroplast genome. This information will be useful for study on the evolution and genetic diversity of P. pruinosa in the future.

The draft genome sequence of a desert tree Populus pruinosa.

Populus pruinosa is a large tree that grows in deserts and shows distinct differences in both morphology and adaptation compared to its sister species, P. euphratica. Here we present a draft genome sequence for P. pruinosa and examine genomic variations between the 2 species. A total of 60 Gb of clean reads from whole-genome sequencing of a P. pruinosa individual were generated using the Illumina HiSeq2000 platform. The assembled genome is 479.3 Mb in length, with an N50 contig size of 14.0 kb and a scaffold size of 698.5 kb; 45.47% of the genome is composed of repetitive elements. We predicted 35 131 protein-coding genes, of which 88.06% were functionally annotated. Gene family clustering revealed 224 unique and 640 expanded gene families in the P. pruinosa genome. Further evolutionary analysis identified numerous genes with elevated values for pairwise genetic differentiation between P. pruinosa and P. euphratica. We provide the genome sequence and gene annotation for P. pruinosa. A large number of genetic variations were recovered by comparison of the genomes between P. pruinosa and P. euphratica. These variations will provide a valuable resource for studying the genetic bases for the phenotypic and adaptive divergence of the 2 sister species.

Distinct patterns of natural selection in Na+/H+ antiporter genes in Populus euphratica and Populus pruinosa.

Salt tolerance genes constitute an important class of loci in plant genomes. Little is known about the extent to which natural selection in saline environments has acted upon these loci, and what types of nucleotide diversity such selection has given rise to. Here, we surveyed genetic diversity in three types of Na+/H+ antiporter gene (SOS, NhaD, and NHX, belonging to the cation/proton antiporter 1 family), which have well-characterized essential roles in plant salt tolerance. Ten Na+/H+ antiporter genes and 16 neutral loci randomly selected as controls were sequenced from 17 accessions of two closely related members of the genus Populus, Populus euphratica and Populus pruinosa, section Turanga, which are native to northwest China. The results show that salt tolerance genes are common targets of natural selection in P. euphratica and P. pruinosa. Moreover, the patterns of nucleotide variation across the three types of Na+/H+ antiporter gene are distinctly different in these two closely related Populus species, and gene flow from P. pruinosa to P. euphratica is highly restricted. Our results suggest that natural selection played an important role in shaping the current distinct patterns of Na+/H+ antiporter genes, resulting in adaptive evolution in P. euphratica and P. pruinosa.