Yongzhi Yang

Genomic insights into salt adaptation in a desert poplar

Despite the high economic and ecological importance of forests, our knowledge of the genomic evolution of trees under salt stress remains very limited. Here we report the genome sequence of the desert poplar, Populus euphratica, which exhibits high tolerance to salt stress. Its genome is very similar and collinear to that of the closely related mesophytic congener, P. trichocarpa. However, we find that several gene families likely to be involved in tolerance to salt stress contain significantly more gene copies within the P. euphratica lineage. Furthermore, genes showing evidence of positive selection are significantly enriched in functional categories related to salt stress. Some of these genes, and others within the same categories, are significantly upregulated under salt stress relative to their expression in another salt-sensitive poplar. Our results provide an important background for understanding tree adaptation to salt stress and facilitating the genetic improvement of cultivated poplars for saline soils.

Yak whole-genome resequencing reveals domestication signatures and prehistoric population expansions

Yak domestication represents an important episode in the early human occupation of the high-altitude Qinghai-Tibet Plateau (QTP). The precise timing of domestication is debated and little is known about the underlying genetic changes that occurred during the process. Here we investigate genome variation of wild and domestic yaks. We detect signals of selection in 209 genes of domestic yaks, several of which relate to behaviour and tameness. We date yak domestication to 7,300 years before present (yr BP), most likely by nomadic people, and an estimated sixfold increase in yak population size by 3,600 yr BP. These dates coincide with two early human population expansions on the QTP during the early-Neolithic age and the late-Holocene, respectively. Our findings add to an understanding of yak domestication and its importance in the early human occupation of the QTP.

Comparative transcriptomic analysis revealed adaptation mechanism of Phrynocephalus erythrurus, the highest altitude Lizard living in the Qinghai-Tibet Plateau

BackgroundOrganisms living at high altitudes must overcome three major environmental challenges: hypoxia, cold, and intense UV radiation. The molecular mechanisms that enable these challenges to be overcome have mainly been studied in endothermic organisms; relatively little attention has been paid to poikilothermic species. Here, we present deep transcriptome sequencing in two closely related lizards, the high altitude-dwelling Phrynocephalus erythrurus and the lowland-dwelling P. putjatia, to identify candidate genes under positive selection and to explore the convergent evolutionary adaptation of poikilothermic animals to high altitude life.ResultsMore than 70 million sequence reads were generated for each species via Illumina sequencing. De novo assembly produced 56,845 and 63,140 transcripts for P. erythrurus and P. putjatia, respectively. P. erythrurus had higher Ka/Ks ratios than P. putjatia, implying an accelerated evolutionary rate in the high altitude lizard lineage. 206 gene ontology (GO) categories with accelerated evolutionary rates and 43 candidate positively selected genes were detected along the P. erythrurus lineage. Some of these GO categories have functions associated with responses to hypoxia, energy metabolism and responses to UV damage. We also found that the high-altitude ranid frog R. kukunoris had higher Ka/Ks ratios than the closely related low-altitude frog R. chensinensis, and that the functional categories with accelerated evolutionary rates in R. kukunoris overlapped extensively with those detected along the P. erythrurus lineage.ConclusionsThe mechanisms of high altitude adaptation in P. erythrurus were tentatively inferred. By comparing two pairs of low- and high-altitude poikilothermic species, we found that similar functional categories had undergone positive selection in high altitude-dwelling Phrynocephalus and Rana lineages, indicating that similar mechanisms of adaptation to high altitude might have evolved in both genera. Our findings provide important guidance for future functional studies on high altitude adaptation in poikilothermic animals.

Genome‐wide variation within and between wild and domestic yak

The yak is one of the few animals that can thrive in the harsh environment of the Qinghai‐Tibetan Plateau and adjacent Alpine regions. Yak provides essential resources allowing Tibetans to live at high altitudes. However, genetic variation within and between wild and domestic yak remain unknown. Here, we present a genome‐wide study of the genetic variation within and between wild and domestic yak. Using next‐generation sequencing technology, we resequenced three wild and three domestic yak with a mean of fivefold coverage using our published domestic yak genome as a reference. We identified a total of 8.38 million SNPs (7.14 million novel), 383 241 InDels and 126 352 structural variants between the six yak. We observed higher linkage disequilibrium in domestic yak than in wild yak and a modest but distinct genetic divergence between these two groups. We further identified more than a thousand of potential selected regions (PSRs) for the three domestic yak by scanning the whole genome. These genomic resources can be further used to study genetic diversity and select superior breeds of yak and other bovid species.

The genome sequence of the wisent (Bison bonasus)

Abstract The wisent, also known as the European bison, was rescued from extinction approximately 80 years ago through the conservation of 12 individuals. Here, we present the draft genome sequence of a male wisent individual descended from this founding stock. A total of 366 billion base pairs (Gb) of raw reads from whole-genome sequencing of this wisent were generated using the Illumina HiSeq2000 platform. The final genome assembly (2.58 Gb) is composed of 29,074 scaffolds with an N50 of 4.7 Mb. 47.3% of the genome is composed of repetitive elements. We identified 21,542 genes and 58,385 non-coding RNAs. A phylogenetic tree based on nuclear genomes indicated sister relationships between bison and wisent and between the wisent-bison clade and yak. For 75 genes we obtained evidence of positive evolution in the wisent lineage. We provide the first genome sequence and gene annotation for the wisent. The availability of these resources will be of value for the future conservation of this endangered large mammal and for reconstructing the evolutionary history of the Bovini tribe.

Different gene expressions between cattle and yak provide insights into high-altitude adaptation.

DNA sequence variation has been widely reported as the genetic basis for adaptation, in both humans and other animals, to the hypoxic environment experienced at high altitudes. However, little is known about the patterns of gene expression underlying such hypoxic adaptations. In this study, we examined the differences in the transcriptomes of four organs (heart, kidney, liver and lung) between yak and cattle, a pair of closely related species distributed at high and low altitudes respectively. Of the four organs examined, heart shows the greatest differentiation between the two species in terms of gene expression profiles. Detailed analyses demonstrated that some genes associated with the oxygen supply system and the defense systems that respond to threats of hypoxia are differentially expressed. In addition, genes with significantly differentiated patterns of expression in all organs exhibited an unexpected uniformity of regulation along with an elevated frequency of nonsynonymous substitutions. This co-evolution of protein sequences and gene expression patterns is likely to be correlated with the optimization of the yak metabolic system to resist hypoxia.

Accumulation of deleterious mutations in the domestic yak genome

Deleterious mutations play an important functional role, affecting trait phenotypes in ways that decrease the fitness of organisms. Estimating the frequency of occurrence and abundance has been a topic of much interest, especially in crops and livestock. The processes of domestication and breeding allow deleterious mutations to persist at high frequency, and identifying such deleterious mutations is particularly important for breed improvement. Here, we assessed genome-wide patterns of deleterious variation in 59 domestic and 13 wild yaks using genome resequencing data. Based on the intersection of results given by three methods (provean, polyphen2 and sift4g), we identified 3187 putative deleterious mutation sites affecting 2586 genes in domestic yaks and 2067 affecting 1701 genes in wild yaks. Multiple lines of evidence indicate a significant increase in the load of deleterious mutations in domesticated yaks compared to wild yaks. Private deleterious genes were found to be associated with the perception of smell and detection of chemical stimulus. We also identified 36 genes related to Mendelian genetic diseases involved in sensory perception, skeletal development and the nervous and immune systems. This study not only adds to the understanding of the genetic basis of yak domestication but also provides a rich catalog of variants that will facilitate future breeding-related research on the yak genome and on other bovid species.