The nonrecombining regions of animal Y chromosomes are known to undergo genetic degeneration, but previous work has failed to reveal large-scale gene degeneration on plant Y chromosomes. Here, we uncover rapid and extensive degeneration of Y-linked genes in a plant species, Silene latifolia, that evolved sex chromosomes de novo in the last 10 million years. Previous transcriptome-based studies of this species missed unexpressed, degenerate Y-linked genes. To identify sex-linked genes, regardless of their expression, we sequenced male and female genomes of S. latifolia and integrated the genomic contigs with a high-density genetic map. This revealed that 45% of Y-linked genes are not expressed, and 23% are interrupted by premature stop codons. This contrasts with X-linked genes, in which only 1.3% of genes contained stop codons and 4.3% of genes were not expressed in males. Loss of functional Y-linked genes is partly compensated for by gene-specific up-regulation of X-linked genes. Our results demonstrate that the rate of genetic degeneration of Y-linked genes in S. latifolia is as fast as in animals, and that the evolutionary trajectories of sex chromosomes are similar in the two kingdoms.sex chromosome evolution | Y degeneration | gene expression | dosage compensation | plants

Many aspects of sex chromosome evolution are common to both plants and animals [1], but the process of Y chromosome degeneration, where genes on the Y become non-functional over time, may be much slower in plants due to purifying selection against deleterious mutations in the haploid gametophyte [2, 3]. Testing for differences in Y degeneration between the kingdoms has been hindered by the absence of accurate age estimates for plant sex chromosomes. Here, we used genome resequencing to estimate the spontaneous mutation rate and the age of the sex chromosomes in white campion (Silene latifolia). Screening of single nucleotide polymorphisms (SNPs) in parents and 10 F progeny identified 39 de novo mutations and yielded a rate of 7.31 × 10 (95% confidence interval: 5.20 × 10 - 8.00 × 10) mutations per site per haploid genome per generation. Applying this mutation rate to the synonymous divergence between homologous X- and Y-linked genes (gametologs) gave age estimates of 11.00 and 6.32 million years for the old and young strata, respectively. Based on SNP segregation patterns, we inferred which genes were Y-linked and found that at least 47% are already dysfunctional. Applying our new estimates for the age of the sex chromosomes indicates that the rate of Y degeneration in S. latifolia is nearly 2-fold slower when compared to animal sex chromosomes of a similar age. Our revised estimates support Y degeneration taking place more slowly in plants, a discrepancy that may be explained by differences in the life cycles of animals and plants.

on behalf of the 100,000 Genomes Project Purpose: Fresh-frozen (FF) tissue is the optimal source of DNA for whole-genome sequencing (WGS) of cancer patients. However, it is not always available, limiting the widespread application of WGS in clinical practice. We explored the viability of using formalin-fixed, paraffin-embedded (FFPE) tissues, available routinely for cancer patients, as a source of DNA for clinical WGS. Methods:We conducted a prospective study using DNAs from matched FF, FFPE, and peripheral blood germ-line specimens collected from 52 cancer patients (156 samples) following routine diagnostic protocols. We compared somatic variants detected in FFPE and matching FF samples. Results:We found the single-nucleotide variant agreement reached 71% across the genome and somatic copy-number alterations (CNAs) detection from FFPE samples was suboptimal (0.44 median correlation with FF) due to nonuniform coverage. CNA detection was improved significantly with lower reverse crosslinking temperature in FFPE DNA extraction (80°C or 65°C depending on the methods). Our final data showed somatic variant detection from FFPE for clinical decision making is possible. We detected 98% of clinically actionable variants (including 30/31 CNAs). Conclusion:We present the first prospective WGS study of cancer patients using FFPE specimens collected in a routine clinical environment proving WGS can be applied in the clinic.Genet Med advance online publication 1 February 2018

Neutral genetic diversity gradients have long been used to infer the colonization history of species [1, 2], but range expansion may also influence the efficacy of natural selection and patterns of non-synonymous polymorphism in different parts of a species' range [3]. Recent theory predicts both an accumulation of deleterious mutations and a reduction in the efficacy of positive selection as a result of range expansion [4-8]. These signatures have been sought in a number of studies of the human range expansion out of Africa, but with contradictory results [9-14]. We analyzed the polymorphism patterns of 578,125 SNPs (17,648 genes) in the European diploid plant Mercurialis annua, which expanded its range from an eastern Mediterranean refugium into western habitats with contrasted climates [15]. Our results confirmed strong signatures of bottlenecks and revealed the accumulation of mildly to strongly deleterious mutations in range-front populations. A significantly higher number of these mutations were homozygous in individuals in range-front populations, pointing to increased genetic load and reduced fitness under a model of recessive deleterious effects. We also inferred a reduction in the number of selective sweeps in range-front versus core populations. These signatures have persisted even in a dioecious herb subject to substantial interpopulation gene flow [15]. Our results extend support from humans to plants for theory on the dynamics of mutations under selection during range expansion, showing that colonization bottlenecks can compromise adaptive potential.

Cannabis sativa has long been an important source of fiber extracted from hemp and both medicinal and recreational drugs based on cannabinoid compounds. Here, we investigated its poorly known domestication history using whole-genome resequencing of 110 accessions from worldwide origins. We show that C. sativa was first domesticated in early Neolithic times in East Asia and that all current hemp and drug cultivars diverged from an ancestral gene pool currently represented by feral plants and landraces in China. We identified candidate genes associated with traits differentiating hemp and drug cultivars, including branching pattern and cellulose/lignin biosynthesis. We also found evidence for loss of function of genes involved in the synthesis of the two major biochemically competing cannabinoids during selection for increased fiber production or psychoactive properties. Our results provide a unique global view of the domestication of C. sativa and offer valuable genomic resources for ongoing functional and molecular breeding research.

Chronic lymphocytic leukaemia (CLL) consists of two biologically and clinically distinct subtypes defined by the abundance of somatic hypermutation (SHM) affecting the Ig variable heavy-chain locus (IgHV). The molecular mechanisms underlying these subtypes are incompletely understood. Here, we present a comprehensive whole-genome sequencing analysis of somatically acquired genetic events from 46 CLL patients, including a systematic comparison of coding and non-coding single-nucleotide variants, copy number variants and structural variants, regions of kataegis and mutation signatures between IgHVmut and IgHVunmut subtypes. We demonstrate that one-quarter of non-coding mutations in regions of kataegis outside the Ig loci are located in genes relevant to CLL. We show that non-coding mutations in ATM may negatively impact on ATM expression and find non-coding and regulatory region mutations in TCL1A, and in IgHVunmut CLL in IKZF3, SAMHD1,PAX5 and BIRC3. Finally, we show that IgHVunmut CLL is dominated by coding mutations in driver genes and an aging signature, whereas IgHVmut CLL has a high incidence of promoter and enhancer mutations caused by aberrant activation-induced cytidine deaminase activity. Taken together, our data support the hypothesis that differences in clinical outcome and biological characteristics between the two subgroups might reflect differences in mutation distribution, incidence and distinct underlying mutagenic mechanisms.

The transformation of chronic lymphocytic leukemia (CLL) to high-grade B-cell lymphoma is known as Richter's Syndrome (RS) and it is a rare event with dismal prognosis. In this study, we conducted whole genome sequencing (WGS) of paired circulating CLL (PB-CLL) and RS biopsies (tissue-RS) from 17 clinical trial (CHOP-O) patients. We found that tissue-RS was enriched for mutations in poor-risk CLL drivers and genes in the DNA damage response (DDR) pathway. In addition, we identified genomic aberrations not previously implicated in RS, including the protein tyrosine phosphatase receptor (PTPRD) and tumour necrosis factor receptor associated factor three (TRAF3). In the non-coding genome, we discovered AID-related and unrelated kataegis in tissue-RS affecting regulatory regions of key immune regulatory genes. These include BTG2, CXCR4, NFATC1, PAX5, NOTCH-1, SLC44A5, FCRL3, SELL, TNIP2 andTRIM13. Furthermore, differences between the global mutation signatures of pairs of PB-CLL and tissue-RS samples implicate DDR as the dominant mechanism driving transformation. Pathway-based clonal de-convolution analysis showed that genes in the MAPK and DDR pathways demonstrate high clonal expansion probability. Direct comparison of nodal-CLL and tissue-RS pairs from an independent cohort confirmed differential expression of the same pathways by RNA expression profiling. Our integrated analysis of WGS and RNA expression data significantly extends previous targeted approaches, which were limited by the lack of germline samples, and it facilitates the identification of novel genomic correlates implicated in RS transformation, which could be targeted therapeutically. Our results inform the future selection of investigative agents for a UK clinical platform study (NCT03899337).

The evolution of sex chromosomes involves the suppression of recombination around a sexdetermining locus, and the subsequent divergence in DNA sequence between the two homologous sex chromosomes. Dioecious plants offer the opportunity to study independent early stages of this process, because of multiple, recent transitions between hermaphroditism and dioecy. Here, we present data from de novo genome assembly and annotation, genetic mapping and transcriptome analysis of the diploid dioecious herb Mercurialis annua, revealing several of the typical hallmarks of early sex-chromosome evolution. Until now only a single sex-linked PCR marker has been published. Our analysis identified a single linkage group, LG10, as the likely sex chromosome, with a region containing 69 sex-linked transcripts with a clearly lower male than female recombination, high X/Y divergence and multiple incidences of premature stop codons on the Y allele. We found many genes with sexbiased expression. Female-biased genes were randomly distributed across the genome, but male-biased genes were slightly enriched on the Y chromosome. Interestingly, Y-linked genes had reduced expression compared with X-linked genes, a pattern consistent with Y chromosome degeneration. M. annua has been a powerful model for the study of rapid sexualsystem transitions in plants; our results here establish it as a model for the study of the early stages of sex-chromosome evolution.