The rise of baobab trees in Madagascar.

The baobab trees (genus Adansonia) have attracted tremendous attention because of their striking shape and distinctive relationships with fauna1. These spectacular trees have also influenced human culture, inspiring innumerable arts, folklore and traditions. Here we sequenced genomes of all eight extant baobab species and argue that Madagascar should be considered the centre of origin for the extant lineages, a key issue in their evolutionary history2,3. Integrated genomic and ecological analyses revealed the reticulate evolution of baobabs, which eventually led to the species diversity seen today. Past population dynamics of Malagasy baobabs may have been influenced by both interspecific competition and the geological history of the island, especially changes in local sea levels. We propose that further attention should be paid to the conservation status of Malagasy baobabs, especially of Adansonia suarezensis and Adansonia grandidieri, and that intensive monitoring of populations of Adansonia za is required, given its propensity for negatively impacting the critically endangered Adansonia perrieri.

Comparative genome anatomy reveals evolutionary insights into a unique amphitriploid fish.

Triploids are rare in nature because of difficulties in meiotic and gametogenic processes, especially in vertebrates. The Carassius complex of cyprinid teleosts contains sexual tetraploid crucian carp/goldfish (C. auratus) and unisexual hexaploid gibel carp/Prussian carp (C. gibelio) lineages, providing a valuable model for studying the evolution and maintenance mechanism of unisexual polyploids in vertebrates. Here we sequence the genomes of the two species and assemble their haplotypes, which contain two subgenomes (A and B), to the chromosome level. Sequencing coverage analysis reveals that C. gibelio is an amphitriploid (AAABBB) with two triploid sets of chromosomes; each set is derived from a different ancestor. Resequencing data from different strains of C. gibelio show that unisexual reproduction has been maintained for over 0.82 million years. Comparative genomics show intensive expansion and alterations of meiotic cell cycle-related genes and an oocyte-specific histone variant. Cytological assays indicate that C. gibelio produces unreduced oocytes by an alternative ameiotic pathway; however, sporadic homologous recombination and a high rate of gene conversion also exist in C. gibelio. These genomic changes might have facilitated purging deleterious mutations and maintaining genome stability in this unisexual amphitriploid fish. Overall, the current results provide novel insights into the evolutionary mechanisms of the reproductive success in unisexual polyploid vertebrates.

Global transcriptome analysis of different stages of preimplantation embryo development in river buffalo.

BACKGROUND: Water buffalo (Bubalus bubalis) are divided into river buffalo and swamp buffalo subspecies and are essential livestock for agriculture and the local economy. Studies on buffalo reproduction have primarily focused on optimal fertility and embryonic mortality. There is currently limited knowledge on buffalo embryonic development, especially during the preimplantation period. Assembly of the river buffalo genome offers a reference for omics studies and facilitates transcriptomic analysis of preimplantation embryo development (PED). METHODS: We revealed transcriptomic profile of four stages (2-cell, 8-cell, Morula and Blastocyst) of PED via RNA-seq (Illumina HiSeq4000). Each stage comprised three biological replicates. The data were analyzed according to the basic RNA-seq analysis process. Ingenuity analysis of cell lineage control, especially transcription factor (TF) regulatory networks, was also performed. RESULTS: A total of 21,519 expressed genes and 67,298 transcripts were predicted from approximately 81.94 Gb of raw data. Analysis of transcriptome-wide expression, gene coexpression networks, and differentially expressed genes (DEGs) allowed for the characterization of gene-specific expression levels and relationships for each stage. The expression patterns of TFs, such as POU5F1, TEAD4, CDX4 and GATAs, were elucidated across diverse time series; most TF expression levels were increased during the blastocyst stage, during which time cell differentiation is initiated. All of these TFs were involved in the composition of the regulatory networks that precisely specify cell fate. These findings offer a deeper understanding of PED at the transcriptional level in the river buffalo.

Correction to: Viral integration drives multifocal HCC during the occult HBV infection.

In the original publication of this article [1], Fig. 6 is wrong and the updated figure is shown below.

Viral integration drives multifocal HCC during the occult HBV infection.

BACKGROUND & AIMS: Although the prognosis of patients with occult hepatitis B virus (HBV) infection (OBI) is usually benign, a small portion may undergo cirrhosis and subsequently hepatocellular carcinoma (HCC). We studied the mechanism of life-long Integration of virus DNA into OBI host's genome, of which may induce hepatocyte transformation. METHODS: We applied HBV capture sequencing on single cells from an OBI patient who, developed multiple HCC tumors and underwent liver resection in May 2013 at Tongji Hospital in China. Despite with the undetectable virus DNA in serum, we determined the pattern of viral integration in tumor cells and adjacent non-tumor cells and obtained the details of the viral arrangement in host genome, and furthermore the HBV integrated region in cancer genome. RESULTS: HBV captured sequencing of tissues and individual cells revealed that samples from multiple tumors shared two viral integration sites that could affect three host genes, including CSMD2 on chr1 and MED30/EXT1 on chr8. Whole genome sequencing further indicated one hybrid chromosome formed by HBV integrations between chr1 and chr8 that was shared by multiple tumors. Additional 50 poorly differentiated liver tumors and the paired adjacent non-tumors were evaluated and functional studies suggested up-regulated EXT1 expression promoted HCC growth. We further observed that the most somatic mutations within the tumor cell genome were common among the multiple tumors, suggesting that HBV associated, multifocal HCC is monoclonal in origin. CONCLUSION: Through analyzing the HBV integration sites in multifocal HCC, our data suggested that the tumor cells were monoclonal in origin and formed in the absence of active viral replication, whereas the affected host genes may subsequently contribute to carcinogenesis.

Draft genome sequence of ramie, Boehmeria nivea (L.) Gaudich.

Ramie, Boehmeria nivea (L.) Gaudich, family Urticaceae, is a plant native to eastern Asia, and one of the world's oldest fibre crops. It is also used as animal feed and for the phytoremediation of heavy metal-contaminated farmlands. Thus, the genome sequence of ramie was determined to explore the molecular basis of its fibre quality, protein content and phytoremediation. For further understanding ramie genome, different paired-end and mate-pair libraries were combined to generate 134.31 Gb of raw DNA sequences using the Illumina whole-genome shotgun sequencing approach. The highly heterozygous B. nivea genome was assembled using the Platanus Genome Assembler, which is an effective tool for the assembly of highly heterozygous genome sequences. The final length of the draft genome of this species was approximately 341.9 Mb (contig N50 = 22.62 kb, scaffold N50 = 1,126.36 kb). Based on ramie genome annotations, 30,237 protein-coding genes were predicted, and the repetitive element content was 46.3%. The completeness of the final assembly was evaluated by benchmarking universal single-copy orthologous genes (BUSCO); 90.5% of the 1,440 expected embryophytic genes were identified as complete, and 4.9% were identified as fragmented. Phylogenetic analysis based on single-copy gene families and one-to-one orthologous genes placed ramie with mulberry and cannabis, within the clade of urticalean rosids. Genome information of ramie will be a valuable resource for the conservation of endangered Boehmeria species and for future studies on the biogeography and characteristic evolution of members of Urticaceae.