Dosage-dependent gene regulation in multicellular eukaryotes: implications for dosage compensation, aneuploid syndromes, and quantitative traits

Behavioral transcriptomic effects of triploidy and probiotic therapy (Bifidobacterium, Lactobacillus, and Lactococcus mixture) on juvenile Chinook salmon (Oncorhynchus tshawytscha)

Aquaculturists use polyploid fish to maximize production albeit with some unintended consequences including compromised behaviors and physiological function. Given benefits of probiotic therapies (e.g., improved immune response, growth, and metabolism), we explored probiotic supplementation (mixture of Bifidobacterium, Lactobacillus, and Lactococcus), to overcome drawbacks. We first examined fish gut bacterial community composition using 16S metabarcoding (via principal coordinate analyses and PERMANOVA) and determined probiotics significantly impacted gut bacteria composition (p = 0.001). Secondly, we examined how a genomic disruptor (triploidy) and diet supplements (probiotics) impact gene transcription and behavioral profiles of hatchery-reared Chinook salmon (Oncorhynchus tshawytscha). Juveniles from four treatment groups (diploid-regular feed, diploid-probiotic feed, triploid-regular feed, and triploid-probiotic feed; n = 360) underwent behavioral assays to test activity, exploration, neophobia, predator evasion, aggression/sociality, behavioral sensitivity, and flexibility. In these fish, transcriptional profiles for genes associated with neural functions (neurogenesis/synaptic plasticity) and biomarkers for stress response and development (growth/appetite) were (i) examined across treatments and (ii) used to describe behavioral phenotypes via principal component analyses and general linear mixed models. Triploids exhibited a more active behavioral profile (p = 0.002), and those on a regular diet had greater Neuropeptide Y transcription (p = 0.02). A growth gene (early growth response protein 1, p = 0.02) and long-term neural development genes (neurogenic differentiation factor, p = 0.003 and synaptysomal-associated protein 25-a, p = 0.005) impacted activity and reactionary profiles, respectively. Overall, our probiotic treatment did not compensate for triploidy. Our research highlights novel applications of behavioral transcriptomics for identifying candidate genes and dynamic, mechanistic associations with complex behavioral repertoires.

Inverse and Proportional Trans Modulation of Gene Expression in Human Aneuploidies

Genomic imbalance in aneuploidy is often detrimental to organisms. To gain insight into the molecular basis of aneuploidies in humans, we analyzed transcriptome data from several autosomal and sex chromosome aneuploidies. The results showed that in human aneuploid cells, genes located on unvaried chromosomes are inversely or proportionally trans-modulated, while a subset of genes on the varied chromosomes are compensated. Less genome-wide modulation is found for sex chromosome aneuploidy compared with autosomal aneuploidy due to X inactivation and the retention of dosage sensitive regulators on both sex chromosomes to limit the effective dosage change. We also found that lncRNA and mRNA can have different responses to aneuploidy. Furthermore, we analyzed the relationship between dosage-sensitive transcription factors and their targets, which illustrated the modulations and indicates genomic imbalance is related to stoichiometric changes in components of gene regulatory complexes.In summary, this study demonstrates the existence of trans-acting effects and compensation mechanisms in human aneuploidies and contributes to our understanding of gene expression regulation in unbalanced genomes and disease states.

Dosage effect genes modulate grain development in synthesized Triticum durum-Haynaldia villosa allohexaploid

Polyploidization in plants often leads to increased cell size and grain size, which may be affected by the increased genome dosage and transcription abundance. The synthesized Triticum durum (AABB)-Haynaldia villosa (VV) amphiploid (AABBVV) has significantly increased grain size, especially grain length, than the tetraploid and diploid parents. To investigate how polyploidization affects grain development at the transcriptional level, we perform transcriptome analysis using the immature seeds of T. durum, H. villosa, and the amphiploid. The dosage effect genes are contributed more by differentially expressed genes from genome V of H. villosa. The dosage effect genes overrepresent grain development-related genes. Interestingly, the vernalization gene TaVRN1 is among the positive dosage effect genes in the T. durum‒H. villosa and T. turgidum‒Ae. tauschii amphiploids. The expression levels of TaVRN1 homologs are positively correlated with the grain size and weight. The TaVRN1-B1 or TaVRN1-D1 mutation shows delayed florescence, decreased cell size, grain size, and grain yield. These data indicate that dosage effect genes could be one of the important explanations for increased grain size by regulating grain development. The identification and functional validation of dosage effect genes may facilitate the finding of valuable genes for improving wheat yield.

Halophytes and heavy metals: A multi-omics approach to understand the role of gene and genome duplication in the abiotic stress tolerance of Cakile maritima

PREMISE

The origin of diversity is a fundamental biological question. Gene duplications are one mechanism that provides raw material for the emergence of novel traits, but evolutionary outcomes depend on which genes are retained and how they become functionalized. Yet, following different duplication types (polyploidy and tandem duplication), the events driving gene retention and functionalization remain poorly understood. Here we used Cakile maritima, a species that is tolerant to salt and heavy metals and shares an ancient whole-genome triplication with closely related salt-sensitive mustard crops (Brassica), as a model to explore the evolution of abiotic stress tolerance following polyploidy.

METHODS

Using a combination of ionomics, free amino acid profiling, and comparative genomics, we characterize aspects of salt stress response in C. maritima and identify retained duplicate genes that have likely enabled adaptation to salt and mild levels of cadmium.

RESULTS

Cakile maritima is tolerant to both cadmium and salt treatments through uptake of cadmium in the roots. Proline constitutes greater than 30% of the free amino acid pool in C. maritima and likely contributes to abiotic stress tolerance. We find duplicated gene families are enriched in metabolic and transport processes and identify key transport genes that may be involved in C. maritima abiotic stress tolerance.

CONCLUSIONS

These findings identify pathways and genes that could be used to enhance plant resilience and provide a putative understanding of the roles of duplication types and retention on the evolution of abiotic stress response.

Polyploid speciation in Zea (Poaceae): cytogenetic insights

MAIN CONCLUSION

The analysis of meiotic pairing affinities and genomic formulae in species and hybrids of Zea allowed us to speculate an evolutionary model to recreate the ancient polyploidization of maize and allied species. The meiotic pairing affinities and the genomic formulae analysis in Zea species and hybrids obtained in new and previous crosses, together with the molecular data known in the genus, allowed us to speculate an evolutionary model to attempt to recreate the ancient polyploidization process of Zea species. We propose that x = 5 semispecies are the ancestors of all modern species of the genus. The complex evolutionary process that originated the different taxa could be included hybridization between sympatric diploid ancestral semispecies (2n = 10) and recurrent duplication of the hybrid chromosome number, resulting in distinct auto- and allopolyploids. After the merger and doubling of independent genomes would have undergone cytological and genetical diploidization, implying revolutionary changes in genome organization and genic balance processes. Based on the meiotic behaviour of the 2n = 30 hybrids, that showed homoeology between the A subgenomes of all parental species, we propose that this subgenome A would be pivotal in all the species and would have conserved the rDNA sequences and the pairing regulator locus (PrZ). In the hypothetical model postulated here, the ancestral semispecies with the pivotal subgenome A would have had a wide geographic distribution, co-occurring and hybridizing with the semispecies harbouring B subgenomes, thus enabling sympatric speciation.

Characteristics and expression of lncRNA and transposable elements in Drosophila aneuploidy

Aneuploidy can globally affect the expression of the whole genome, which is detrimental to organisms. Dosage-sensitive regulators usually have multiple intermolecular interactions, and changes in their stoichiometry are responsible for the dysregulation of the regulatory network. Currently, studies on noncoding genes in aneuploidy are relatively rare. We studied the characteristics and expression profiles of long noncoding RNAs (lncRNAs) and transposable elements (TEs) in aneuploid Drosophila. It is found that lncRNAs and TEs are affected by genomic imbalance and appear to be more sensitive to an inverse dosage effect than mRNAs. Several dosage-sensitive lncRNAs and TEs were detected for their expression patterns during embryogenesis, and their biological functions in the ovary and testes were investigated using tissue-specific RNAi. This study advances our understanding of the noncoding sequences in imbalanced genomes and provides a novel perspective for the study of aneuploidy-related human diseases such as cancer.

Tackling redundancy: genetic mechanisms underlying paralog compensation in plants

Gene duplication is a powerful source of biological innovation giving rise to paralogous genes that undergo diverse fates. Redundancy between paralogous genes is an intriguing outcome of duplicate gene evolution, and its maintenance over evolutionary time has long been considered a paradox. Redundancy can also be dubbed 'a geneticist's nightmare': It hinders the predictability of genome editing outcomes and limits our ability to link genotypes to phenotypes. Genetic studies in yeast and plants have suggested that the ability of ancient redundant duplicates to compensate for dosage perturbations resulting from a loss of function depends on the reprogramming of gene expression, a phenomenon known as active compensation. Starting from considerations on the stoichiometric constraints that drive the evolutionary stability of redundancy, this review aims to provide insights into the mechanisms of active compensation between duplicates that could be targeted for breaking paralog dependencies - the next frontier in plant functional studies.

Chromosome translocation affects multiple phenotypes, causes genome-wide dysregulation of gene expression, and remodels metabolome in hexaploid wheat

Chromosomal rearrangements (CRs) may occur in newly formed polyploids due to compromised meiotic fidelity. Moreover, CRs can be more readily tolerated in polyploids allowing their longer-term retention and hence potential spreading/fixation within a lineage. The direct functional consequences of CRs in plant polyploids remain unexplored. Here, we identified a heterozygous individual from a synthetic allohexaploid wheat in which the terminal parts of the long-arms of chromosomes 2D (approximately 193 Mb) and 4A (approximately 167 Mb) were reciprocally translocated. Five homogeneous translocation lines including both unbalanced and balanced types were developed by selfing fertilization of the founder mutant (RT [2DL; 4AL]-ter/1, reciprocal translocation). We investigated impacts of these translocations on phenotype, genome-wide gene expression and metabolome. We find that, compared with sibling wild-type, CRs in the form of both unbalanced and balanced translocations induced substantial changes of gene expression primarily via trans-regulation in the nascent allopolyploid wheat. The CRs also manifested clear phenotypic and metabolic consequences. In particular, the genetically balanced, stable reciprocal translocations lines showed immediate enhanced reproductive fitness relative to wild type. Our results underscore the profound impact of CRs on gene expression in nascent allopolyploids with wide-ranging phenotypic and metabolic consequences, suggesting CRs are an important source of genetic variation that can be exploited for crop breeding.

Dosage-sensitivity shapes how genes transcriptionally respond to allopolyploidy and homoeologous exchange in resynthesized Brassica napus

The gene balance hypothesis proposes that selection acts on the dosage (i.e. copy number) of genes within dosage-sensitive portions of networks, pathways, and protein complexes to maintain balanced stoichiometry of interacting proteins, because perturbations to stoichiometric balance can result in reduced fitness. This selection has been called dosage balance selection. Dosage balance selection is also hypothesized to constrain expression responses to dosage changes, making dosage-sensitive genes (those encoding members of interacting proteins) experience more similar expression changes. In allopolyploids, where whole-genome duplication involves hybridization of diverged lineages, organisms often experience homoeologous exchanges that recombine, duplicate, and delete homoeologous regions of the genome and alter the expression of homoeologous gene pairs. Although the gene balance hypothesis makes predictions about the expression response to homoeologous exchanges, they have not been empirically tested. We used genomic and transcriptomic data from 6 resynthesized, isogenic Brassica napus lines over 10 generations to identify homoeologous exchanges, analyzed expression responses, and tested for patterns of genomic imbalance. Groups of dosage-sensitive genes had less variable expression responses to homoeologous exchanges than dosage-insensitive genes, a sign that their relative dosage is constrained. This difference was absent for homoeologous pairs whose expression was biased toward the B. napus A subgenome. Finally, the expression response to homoeologous exchanges was more variable than the response to whole-genome duplication, suggesting homoeologous exchanges create genomic imbalance. These findings expand our knowledge of the impact of dosage balance selection on genome evolution and potentially connect patterns in polyploid genomes over time, from homoeolog expression bias to duplicate gene retention.

Transcriptional Interactions of Single B-Subgenome Chromosome with C-Subgenome in B. oleracea-nigra Additional Lines

Serial monosomic alien addition lines (MAALs) provide an ideal system to elucidate the transcriptomic interactions between the alien chromosomes and recipient genome under aneuploidy. Herein, five available Brassica oleracea-nigra MAALs (CCB1, CCB4, CCB5, CCB6, CCB8), their derived B. oleracea plants (non-MAALs), and two parents were analyzed for their gene expressions by using high-throughput technology. Compared to parental B. oleracea, all MAALs showed various numbers of DEGs, but CCB8 gave much higher DEGs; the number of downregulated DEGs was slightly higher than the number of upregulated ones, except for in relation to CCB8. All derived B. oleracea plants also gave certain numbers of DEGs, despite these being much lower than in the respective MAALs. Compared to B. nigra, in all five MAALs more DEGs were downregulated than upregulated. Trans-effects were likely more prevailing than cis-effects, and these DEGs were predominantly associated with material transport by dysregulating the cellular component. Meanwhile, the orthologous genes on alien chromosomes could only play a feeble compensatory role for those gene pairs in C-subgenome, and different levels of the expressed genes had a greater tendency towards downregulation. These results revealed transcriptional aneuploidy response patterns between two genomes and suggested that cis- and trans-mechanisms synergistically regulated alien gene transcriptions after distant hybridization.

Genome-Wide Expression Analysis of Long Noncoding RNAs and Their Target Genes in Metafemale Drosophila

Aneuploidy is usually more detrimental than altered ploidy of the entire set of chromosomes. To explore the regulatory mechanism of gene expression in aneuploidy, we analyzed the transcriptome sequencing data of metafemale Drosophila. The results showed that most genes on the X chromosome undergo dosage compensation, while the genes on the autosomal chromosomes mainly present inverse dosage effects. Furthermore, long noncoding RNAs (lncRNAs) have been identified as key regulators of gene expression, and they are more sensitive to dosage changes than mRNAs. We analyzed differentially expressed mRNAs (DEGs) and differentially expressed lncRNAs (DELs) in metafemale Drosophila and performed functional enrichment analyses of DEGs and the target genes of DELs, and we found that they are involved in several important biological processes. By constructing lncRNA-mRNA interaction networks and calculating the maximal clique centrality (MCC) value of each node in the network, we also identified two key candidate lncRNAs (CR43940 and CR42765), and two of their target genes, Sin3A and MED1, were identified as inverse dosage modulators. These results suggest that lncRNAs play an important role in the regulation of genomic imbalances. This study may deepen the understanding of the gene expression regulatory mechanisms in aneuploidy from the perspective of lncRNAs.

Dosage balance acts as a time-dependent selective barrier to subfunctionalization

BACKGROUND

Gene duplication is an important process for genome expansion, sometimes allowing for new gene functions to develop. Duplicate genes can be retained through multiple processes, either for intermediate periods of time through processes such as dosage balance, or over extended periods of time through processes such as subfunctionalization and neofunctionalization.

RESULTS

Here, we built upon an existing subfunctionalization Markov model by incorporating dosage balance to describe the interplay between subfunctionalization and dosage balance to explore selective pressures on duplicate copies. Our model incorporates dosage balance using a biophysical framework that penalizes the fitness of genetic states with stoichiometrically imbalanced proteins. These imbalanced states cause increased concentrations of exposed hydrophobic surface areas, which cause deleterious mis-interactions. We draw comparison between our Subfunctionalization + Dosage-Balance Model (Sub + Dos) and the previous Subfunctionalization-Only (Sub-Only) Model. This comparison includes how the retention probabilities change over time, dependent upon the effective population size and the selective cost associated with spurious interaction of dosage-imbalanced partners. We show comparison between Sub-Only and Sub + Dos models for both whole-genome duplication and small-scale duplication events.

CONCLUSION

These comparisons show that following whole-genome duplication, dosage balance serves as a time-dependent selective barrier to the subfunctionalization process, by causing an overall delay but ultimately leading to a larger portion of the genome retained through subfunctionalization. This higher percentage of the genome that is ultimately retained is caused by the alternative competing process, nonfunctionalization, being selectively blocked to a greater extent. In small-scale duplication, the reverse pattern is seen, where dosage balance drives faster rates of subfunctionalization, but ultimately leads to a smaller portion of the genome retained as duplicates. This faster rate of subfunctionalization is because the dosage balance of interacting gene products is negatively affected immediately after duplication and the loss of a duplicate restores the stoichiometric balance. Our findings provide support that the subfunctionalization of genes that are susceptible to dosage balance effects, such as proteins involved in complexes, is not a purely neutral process. With stronger selection against stoichiometrically imbalanced gene partners, the rates of subfunctionalization and nonfunctionalization slow; however, this ultimately leads to a greater proportion of subfunctionalized gene pairs.

Genomic imbalance modulates transposable element expression in maize

Genomic imbalance refers to the more severe phenotypic consequences of changing part of a chromosome compared with the whole genome set. Previous genome imbalance studies in maize have identified prevalent inverse modulation of genes on the unvaried chromosomes (trans) with both the addition or subtraction of chromosome arms. Transposable elements (TEs) comprise a substantial fraction of the genome, and their reaction to genomic imbalance is therefore of interest. Here, we analyzed TE expression using RNA-seq data of aneuploidy and ploidy series and found that most aneuploidies showed an inverse modulation of TEs, but reductions in monosomy and increases in disomy and trisomy were also common. By contrast, the ploidy series showed little TE modulation. The modulation of TEs and genes in the same experimental group were compared, and TEs showed greater modulation than genes, especially in disomy. Class I and II TEs were differentially modulated in most aneuploidies, and some superfamilies in each TE class also showed differential modulation. Finally, the significantly upregulated TEs in three disomies (TB-7Lb, TB9Lc, and TB-10L19) did not increase the proportion of adjacent gene expression when compared with non-differentially expressed TEs, indicating that modulations of TEs do not compound the effect on genes. These results suggest that the prevalent inverse TE modulation in aneuploidy results from stoichiometric upset of the regulatory machinery used by TEs, similar to the response of core genes to genomic imbalance.

Comparative transcriptomics analysis at the key stage of maize ear development dissect heterosis

Important traits related to maize (Zea mays L.) grain yield, such as kernel row number, ear length, kernel number per row, are determined during the development of female inflorescence. There is a significant positive correlation between yield component and the activity of inflorescence meristem (IM). To find the key stage of heterosis in the development of the ear, immature ears (from the IM stage until the end of the floral meristem [FM] stage) of Yudan888 and its parent lines were sampled to assay phenotype and for comparative transcriptomics analysis. The immature ear length of Yudan888 at the IM stage fitted an additive (mid-parental) model, but it showed high parental dominance at the spikelet-pair meristem (SPM) stage. Comparative analysis of transcriptomes suggested significant differences between additive and nonadditive expression patterns for different developmental stages. The number of distinct maternal or paternal genes (DMP) (genes expressed only in one parental line and their hybrid but silenced in another line) was greater than ABF1 (genes expressed in both parental lines but silenced in hybrid) at each stage. Gene Ontology (GO) enrichment suggested that the cell redox homeostasis genes with overdominance expression patterns in hybrids have an important contribution to heterosis. According to our research, an ear length heterosis network was established. The discovery of the inflection point for ear length heterosis allows us for inferring that the transition state of IM to SPM may be the starting point of ear length heterosis. These findings improved the understanding of maize ear length heterosis.

MicroRNAs play regulatory roles in genomic balance

Classic genetics studies found that genomic imbalance caused by changing the dosage of part of the genome (aneuploidy) has more detrimental effects than altering the dosage of the whole genome (ploidy). Previous analysis revealed global modulation of gene expression triggered by aneuploidy across various species, including maize (Zea mays), Arabidopsis, yeast, mammals, etc. Plant microRNAs (miRNAs) are a class of 20- to 24-nt endogenous small noncoding RNAs that carry out post-transcriptional gene expression regulation. That miRNAs and their putative targets are preferentially retained as duplicates after whole-genome duplication, as are many transcription factors and signaling components, indicates miRNAs are likely to be dosage-sensitive and potentially involved in genomic balance networks. This review addresses the following questions regarding the role of miRNAs in genomic imbalance. (1) How do aneuploidy and polyploidy impact the expression of miRNAs? (2) Do miRNAs play a regulatory role in modulating the expression of their targets under genomic imbalance?

Anther Culture-Derived Haploids of Citrus aurantium L. (Sour Orange) and Genetic Verification of Haploid-Derived Regenerated Plants

Citrus plants are important fruit tree species; however, the breeding of high-quality varieties of citrus species is a time-consuming process. Using haploid-derived plants from anther culture may reduce the time required for obtaining purebred lines. This study aimed to genetically verify whether anther culture-derived sour orange (Citrus aurantium L.) plants developed from somatic embryos or haploid tissues. Sour orange anthers were cultured in N6 and MS media to induce calli and somatic embryos. N6 liquid medium supplemented with 1 mg·L^-1 gibberellic acid and 200 µM spermidine resulted in a 10% increase in callus and embryo induction rates. Regenerated plants were validated using simple sequence repeat markers. Out of the 109 regenerated plants, ploidy analysis identified 99 diploids, two haploids, and eight putative aneuploids; out of the 99 diploid plants, 33 were haploid-derived homozygous diploids. The chromosomal analysis confirmed most plants as diploids, whereas some were identified as aneuploids (19-21 chromosomes). Furthermore, phylogenetic analysis confirmed that the resultant homozygous or heterozygous plants were haploid-derived. This is the first report of haploid-derived homozygous diploid and aneuploid sour orange plants obtained through anther culture. Moreover, the anther cultivation technique described herein can be applied to other citrus varieties.

The multiple fates of gene duplications: Deletion, hypofunctionalization, subfunctionalization, neofunctionalization, dosage balance constraints, and neutral variation

Gene duplications have long been recognized as a contributor to the evolution of genes with new functions. Multiple copies of genes can result from tandem duplication, from transposition to new chromosomes, or from whole-genome duplication (polyploidy). The most common fate is that one member of the pair is deleted to return the gene to the singleton state. Other paths involve the reduced expression of both copies (hypofunctionalization) that are held in duplicate to maintain sufficient quantity of function. The two copies can split functions (subfunctionalization) or can diverge to generate a new function (neofunctionalization). Retention of duplicates resulting from doubling of the whole genome occurs for genes involved with multicomponent interactions such as transcription factors and signal transduction components. In contrast, these classes of genes are underrepresented in small segmental duplications. This complementary pattern suggests that the balance of interactors affects the fate of the duplicate pair. We discuss the different mechanisms that maintain duplicated genes, which may change over time and intersect.

Heterosis of fitness and phenotypic variance in the evolution of a diploid gene regulatory network

Heterosis describes the phenomenon, whereby a hybrid population has higher fitness than an inbred population, which has previously been explained by either Mendelian dominance or overdominance under the general assumption of a simple genotype-phenotype relationship. However, recent studies have demonstrated that genes interact through a complex gene regulatory network (GRN). Furthermore, phenotypic variance is reportedly lower for heterozygotes, and the origin of such variance-related heterosis remains elusive. Therefore, a theoretical analysis linking heterosis to GRN evolution and stochastic gene expression dynamics is required. Here, we investigated heterosis related to fitness and phenotypic variance in a system with interacting genes by numerically evolving diploid GRNs. According to the results, the heterozygote population exhibited higher fitness than the homozygote population, indicating fitness-related heterosis resulting from evolution. In addition, the heterozygote population exhibited lower noise-related phenotypic variance in expression levels than the homozygous population, implying that the heterozygote population is more robust to noise. Furthermore, the distribution of the ratio of heterozygote phenotypic variance to homozygote phenotypic variance exhibited quantitative similarity with previous experimental results. By applying dominance and differential gene expression rather than only a single gene expression model, we confirmed the correlation between heterosis and differential gene expression. We explain our results by proposing that the convex high-fitness region is evolutionarily shaped in the genetic space to gain noise robustness under genetic mixing through sexual reproduction. These results provide new insights into the effects of GRNs on variance-related heterosis and differential gene expression.

Pentaploidization Enriches the Genetic Diversity of Wheat by Enhancing the Recombination of AB Genomes

Allohexaploidization and continuous introgression play a key role in the origin and evolution of bread wheat. The genetic bottleneck of bread wheat resulting from limited germplasms involved in the origin and modern breeding may be compensated by gene flow from tetraploid wheat through introgressive hybridization. The inter-ploidy hybridization between hexaploid and tetraploid wheat generates pentaploid hybrids first, which absorbed genetic variations both from hexaploid and tetraploid wheat and have great potential for re-evolution and improvement in bread wheat. Therefore, understanding the effects of the pentaploid hybrid is of apparent significance in our understanding of the historic introgression and in informing breeding. In the current study, two sets of F2 populations of synthetic pentaploid wheat (SPW1 and SPW2) and synthetic hexaploid wheat (SHW1 and SHW2) were created to analyze differences in recombination frequency (RF) of AB genomes and distorted segregation of polymorphic SNP markers through SNP genotyping. Results suggested that (1) the recombination of AB genomes in the SPW populations was about 3- to 4-fold higher than that in the SHW populations, resulting from the significantly (P < 0.01) increased RF between adjacent and linked SNP loci, especially the variations that occurred in a pericentromeric region which would further enrich genetic diversity; (2) the crosses of hexaploid × tetraploid wheat could be an efficient way to produce pentaploid derivatives than the crosses of tetraploid × hexaploid wheat according to the higher germination rate found in the former crosses; (3) the high proportion of distorted segregation loci that skewed in favor of the female parent genotype/allele in the SPW populations might associate with the fitness and survival of the offspring. Based on the presented data, we propose that pentaploid hybrids should increasingly be used in wheat breeding. In addition, the contribution of gene flow from tetraploid wheat to bread wheat mediated by pentaploid introgressive hybridization also was discussed in the re-evolution of bread wheat.

Dosage-sensitive miRNAs trigger modulation of gene expression during genomic imbalance in maize

The genomic imbalance caused by varying the dosage of individual chromosomes or chromosomal segments (aneuploidy) has more detrimental effects than altering the dosage of complete chromosome sets (ploidy). Previous analysis of maize (Zea mays) aneuploids revealed global modulation of gene expression both on the varied chromosome (cis) and the remainder of the genome (trans). However, little is known regarding the role of microRNAs (miRNAs) under genomic imbalance. Here, we report the impact of aneuploidy and polyploidy on the expression of miRNAs. In general, cis miRNAs in aneuploids present a predominant gene-dosage effect, whereas trans miRNAs trend toward the inverse level, although other types of responses including dosage compensation, increased effect, and decreased effect also occur. By contrast, polyploids show less differential miRNA expression than aneuploids. Significant correlations between expression levels of miRNAs and their targets are identified in aneuploids, indicating the regulatory role of miRNAs on gene expression triggered by genomic imbalance.

Effect of aneuploidy of a non-essential chromosome on gene expression in maize

The non-essential supernumerary maize (Zea mays) B chromosome (B) has recently been shown to contain active genes and to be capable of impacting gene expression of the A chromosomes. However, the effect of the B chromosome on gene expression is still unclear. In addition, it is unknown whether the accumulation of the B chromosome has a cumulative effect on gene expression. To examine these questions, the global expression of genes, microRNAs (miRNAs), and transposable elements (TEs) of leaf tissue of maize W22 plants with 0-7 copies of the B chromosome was studied. All experimental genotypes with B chromosomes displayed a trend of upregulated gene expression for a subset of A-located genes compared to the control. Over 3000 A-located genes are significantly differentially expressed in all experimental genotypes with the B chromosome relative to the control. Modulations of these genes are largely determined by the presence rather than the copy number of the B chromosome. By contrast, the expression of most B-located genes is positively correlated with B copy number, showing a proportional gene dosage effect. The B chromosome also causes increased expression of A-located miRNAs. Differentially expressed miRNAs potentially regulate their targets in a cascade of effects. Furthermore, the varied copy number of the B chromosome leads to the differential expression of A-located and B-located TEs. The findings provide novel insights into the function and properties of the B chromosome.

Plant cytoplasmic ribosomal proteins: an update on classification, nomenclature, evolution and resources

Standardized naming systems are essential to integrate and unify distinct research fields, and to link multi-species data within and across kingdoms. We conducted a comprehensive survey of cytoplasmic ribosomal proteins (CRPs) in the dicot model Arabidopsis thaliana and the monocot model rice, noting that the standardized naming system has not been widely adopted in the plant community. We generated a database linking the old classical names to their updated and compliant names. We also explored the sequences, molecular evolution, and structural and functional characteristics of all plant CRP families, emphasizing evolutionarily conserved and plant-specific features through cross-kingdom comparisons. Unlike fungal CRP paralogs that were mainly created by whole-genome duplication (WGD) or retroposition under a concerted evolution mode, plant CRP genes evolved primarily through both WGD and tandem duplications in a rapid birth-and-death process. We also provide a web-based resource (http://www.plantcrp.cn/) with the aim of sharing the latest knowledge on plant CRPs and facilitating the continued development of a standardized framework across the entire community.

Machine learning approaches to identify core and dispensable genes in pangenomes

A gene in a given taxonomic group is either present in every individual (core) or absent in at least a single individual (dispensable). Previous pangenomic studies have identified certain functional differences between core and dispensable genes. However, identifying if a gene belongs to the core or dispensable portion of the genome requires the construction of a pangenome, which involves sequencing the genomes of many individuals. Here we aim to leverage the previously characterized core and dispensable gene content for two grass species [Brachypodium distachyon (L.) P. Beauv. and Oryza sativa L.] to construct a machine learning model capable of accurately classifying genes as core or dispensable using only a single annotated reference genome. Such a model may mitigate the need for pangenome construction, an expensive hurdle especially in orphan crops, which often lack the adequate genomic resources.

One Hundred Years of Gene Balance: How Stoichiometric Issues Affect Gene Expression, Genome Evolution, and Quantitative Traits

A century ago experiments with the flowering plant Datura stramonium and the fruit fly Drosophila melanogaster revealed that adding an extra chromosome to a karyotype was much more detrimental than adding a whole set of chromosomes. This phenomenon was referred to as gene balance and has been recapitulated across eukaryotic species. Here, we retrace some developments in this field. Molecular studies suggest that the basis of balance involves stoichiometric relationships of multi-component interactions. This concept has implication for the mechanisms controlling gene expression, genome evolution, sex chromosome evolution/dosage compensation, speciation mechanisms, and the underlying genetics of quantitative traits.

Modulation of Global Gene Expression by Aneuploidy and CNV of Dosage Sensitive Regulatory Genes

Aneuploidy, which disrupts the genetic balance due to partial genome dosage changes, is usually more detrimental than euploidy variation. To investigate the modulation of gene expression in aneuploidy, we analyzed the transcriptome sequencing data of autosomal and sex chromosome trisomy in Drosophila. The results showed that most genes on the varied chromosome (cis) present dosage compensation, while the remainder of the genome (trans) produce widespread inverse dosage effects. Some altered functions and pathways were identified as the common characteristics of aneuploidy, and several possible regulatory genes were screened for an inverse dosage effect. Furthermore, we demonstrated that dosage changes of inverse regulator Inr-a/pcf11 can produce a genome-wide inverse dosage effect. All these findings suggest that the mechanism of genomic imbalance is related to the changes in the stoichiometric relationships of macromolecular complex members that affect the overall function. These studies may deepen the understanding of gene expression regulatory mechanisms.

Role of long non-coding RNAs in Down syndrome patients: a transcriptome analysis study

Down syndrome (DS) is defined by the presence of a third copy of chromosome 21. Several comorbidities can be found in these patients, such as intellectual disability (ID), muscle weakness, hypotonia, congenital heart disease, and autoimmune diseases. The molecular mechanisms playing a role in the development of such comorbidities are still unclear. The regulation and expression of genes that map to chromosome 21 are dynamic and complex, so it is important to perform global gene expression studies with high statistical power to fully characterize the transcriptome in DS patients. This study was undertaken to evaluate mRNAs and lncRNA expression in patients with DS versus a matched cohort of healthy subjects. RNA sequencing was used to perform this transcriptome study. Differential expression analysis revealed 967 transcripts with padj ≤ 0.05. Among them, 447 transcripts were differentially expressed in patients with DS compared to controls. Particularly, 203 transcripts were down expressed (151 protein-coding mRNAs, 45 lncRNAs, 1 microRNA, 1 mitochondrial tRNA, 1 ribozyme, and 1 small nuclear RNA) and 244 were over expressed (210 protein-coding mRNAs and 34 lncRNAs). Interestingly, deregulated lncRNAs are involved in pathways that play a role in developmental disorders, neurological diseases, DNA replication and repair mechanisms, and cancer development in DS patients. In conclusion, these results suggest a role of lncRNAs in the phenotype of DS patients.

Genomic imbalance determines positive and negative modulation of gene expression in diploid maize

Genomic imbalance caused by changing the dosage of individual chromosomes (aneuploidy) has a more detrimental effect than varying the dosage of complete sets of chromosomes (ploidy). We examined the impact of both increased and decreased dosage of 15 distal and 1 interstitial chromosomal regions via RNA-seq of maize (Zea mays) mature leaf tissue to reveal new aspects of genomic imbalance. The results indicate that significant changes in gene expression in aneuploids occur both on the varied chromosome (cis) and the remainder of the genome (trans), with a wider spread of modulation compared with the whole-ploidy series of haploid to tetraploid. In general, cis genes in aneuploids range from a gene-dosage effect to dosage compensation, whereas for trans genes the most common effect is an inverse correlation in that expression is modulated toward the opposite direction of the varied chromosomal dosage, although positive modulations also occur. Furthermore, this analysis revealed the existence of increased and decreased effects in which the expression of many genes under genome imbalance are modulated toward the same direction regardless of increased or decreased chromosomal dosage, which is predicted from kinetic considerations of multicomponent molecular interactions. The findings provide novel insights into understanding mechanistic aspects of gene regulation.

Predominantly inverse modulation of gene expression in genomically unbalanced disomic haploid maize

The phenotypic consequences of the addition or subtraction of part of a chromosome is more severe than changing the dosage of the whole genome. By crossing diploid trisomies to a haploid inducer, we identified 17 distal segmental haploid disomies that cover ∼80% of the maize genome. Disomic haploids provide a level of genomic imbalance that is not ordinarily achievable in multicellular eukaryotes, allowing the impact to be stronger and more easily studied. Transcriptome size estimates revealed that a few disomies inversely modulate most of the transcriptome. Based on RNA sequencing, the expression levels of genes located on the varied chromosome arms (cis) in disomies ranged from being proportional to chromosomal dosage (dosage effect) to showing dosage compensation with no expression change with dosage. For genes not located on the varied chromosome arm (trans), an obvious trans-acting effect can be observed, with the majority showing a decreased modulation (inverse effect). The extent of dosage compensation of varied cis genes correlates with the extent of trans inverse effects across the 17 genomic regions studied. The results also have implications for the role of stoichiometry in gene expression, the control of quantitative traits, and the evolution of dosage-sensitive genes.

The Gene Expression Profile of the Song Control Nucleus HVC Shows Sex Specificity, Hormone Responsiveness, and Species Specificity Among Songbirds

Singing occurs in songbirds of both sexes, but some species show typical degrees of sex-specific performance. We studied the transcriptional sex differences in the HVC, a brain nucleus critical for song pattern generation, of the forest weaver (Ploceus bicolor), the blue-capped cordon-bleu (Uraeginthus cyanocephalus), and the canary (Serinus canaria), which are species that show low, medium, and high levels of sex-specific singing, respectively. We observed persistent sex differences in gene expression levels regardless of the species-specific sexual singing phenotypes. We further studied the HVC transcriptomes of defined phenotypes of canary, known for its testosterone-sensitive seasonal singing. By studying both sexes of canaries during both breeding and non-breeding seasons, non-breeding canaries treated with testosterone, and spontaneously singing females, we found that the circulating androgen levels and sex were the predominant variables associated with the variations in the HVC transcriptomes. The comparison of natural singing with testosterone-induced singing in canaries of the same sex revealed considerable differences in the HVC transcriptomes. Strong transcriptional changes in the HVC were detected during the transition from non-singing to singing in canaries of both sexes. Although the sex-specific genes of singing females shared little resemblance with those of males, our analysis showed potential functional convergences. Thus, male and female songbirds achieve comparable singing behaviours with sex-specific transcriptomes.

High resolution RNA-seq profiling of genes encoding ribosomal proteins across different organs and developmental stages in Arabidopsis thaliana

In Arabidopsis thaliana, each ribosomal protein (RP) is encoded by a small gene family consisting of two or more highly homologous paralogues, which results in ribosome heterogeneity. It is largely unknown that how genes from multiple member containing RP families are regulated at transcriptional level to accommodate the needs of different plant organs and developmental stages. In this study, we investigated the transcript accumulation profiles of RP genes and found that the expression levels of RP genes are varied dramatically in different organs and developmental stages. Although most RP genes are found to be ubiquitously transcribed, some are obviously transcribed with spatiotemporal specificity. The hierarchical clustering trees of transcript accumulation intensity of RP genes revealed that different organs and developmental stages have different population of RP gene transcripts. By interrogating of the expression fluctuation trend of RP genes, we found that in spite of the fact that most groups of paralogous RP genes are transcribed in concerted manners, some RPs gene have contrasting expression patterns. When transcripts of paralogous RP genes from the same family are considered together, the expression level of most RP genes are well-matched but some are obviously higher or lower, therefore we speculate that some superfluous RPs may act outside the ribosome and a portion of ribosomes may lack one or even more RP(s). Altogether, our analysis results suggested that functional divergence may exist among heterogeneous ribosomes that resulted from different combination of RP paralogues, and substoichiometry of several RP gene families may lead to another layer of heterogeneous ribosomes which also have divergent functions in plants.

An empirical bayesian approach for testing gene expression fold change and its application in detecting global dosage effects

We are motivated by biological studies intended to understand global gene expression fold change. Biologists have generally adopted a fixed cutoff to determine the significance of fold changes in gene expression studies (e.g. by using an observed fold change equal to two as a fixed threshold). Scientists can also use a t-test or a modified differential expression test to assess the significance of fold changes. However, these methods either fail to take advantage of the high dimensionality of gene expression data or fail to test fold change directly. Our research develops a new empirical Bayesian approach to substantially improve the power and accuracy of fold-change detection. Specifically, we more accurately estimate gene-wise error variation in the log of fold change. We then adopt a t-test with adjusted degrees of freedom for significance assessment. We apply our method to a dosage study in Arabidopsis and a Down syndrome study in humans to illustrate the utility of our approach. We also present a simulation study based on real datasets to demonstrate the accuracy of our method relative to error variance estimation and power in fold-change detection. Our developed R package with a detailed user manual is publicly available on GitHub at https://github.com/cuiyingbeicheng/Foldseq.

GmKIX8-1 regulates organ size in soybean and is the causative gene for the major seed weight QTL qSw17-1

Seed weight is one of the most important agronomic traits in soybean for yield improvement and food production. Several quantitative trait loci (QTLs) associated with the trait have been identified in soybean. However, the genes underlying the QTLs and their functions remain largely unknown. Using forward genetic methods and CRISPR/Cas9 gene editing, we identified and characterized the role of GmKIX8-1 in the control of organ size in soybean. GmKIX8-1 belongs to a family of KIX domain-containing proteins that negatively regulate cell proliferation in plants. Consistent with this predicted function, we found that loss-of-function GmKIX8-1 mutants showed a significant increase in the size of aerial plant organs, such as seeds and leaves. Likewise, the increase in organ size is due to increased cell proliferation, rather than cell expansion, and increased expression of CYCLIN D3;1-10. Lastly, molecular analysis of soybean germplasms harboring the qSw17-1 QTL for the big-seeded phenotype indicated that reduced expression of GmKIX8-1 is the genetic basis of the qSw17-1 phenotype.

The Gene Balance Hypothesis: Epigenetics and Dosage Effects in Plants

Dosage effects in plants are caused by changes in the copy number of chromosomes, segments of chromosomes, or multiples of individual genes. Genes often exhibit a dosage effect in which the amount of product is closely correlated with the number of copies present. However, when larger segments of chromosomes are varied, there are trans-acting effects across the genome that are unleashed that modulate gene expression in cascading effects. These appear to be mediated by the stoichiometric relationship of gene regulatory machineries. There are both positive and negative modulations of target gene expression, but the latter is the plurality effect. When this inverse effect is combined with a dosage effect, compensation for a gene can occur in which its expression is similar to the normal diploid regardless of the change in chromosomal dosage. In contrast, changing the whole genome in a polyploidy series has fewer relative effects as the stoichiometric relationship is not disrupted. Together, these observations suggest that the stoichiometry of gene regulation is important as a reflection of the mode of assembly of the individual subunits involved in the effective regulatory macromolecular complexes. This principle has implications for gene expression mechanisms, quantitative trait genetics, and the evolution of genes depending on the mode of duplication, either segmentally or via whole-genome duplication.

Two novel heteropolymer-forming proteins maintain the multicellular shape of the cyanobacterium Anabaena sp. PCC 7120

Polymerizing and filament-forming proteins are instrumental for numerous cellular processes such as cell division and growth. Their function in stabilization and localization of protein complexes and replicons is achieved by a filamentous structure. Known filamentous proteins assemble into homopolymers consisting of single subunits - for example, MreB and FtsZ in bacteria - or heteropolymers that are composed of two subunits, for example, keratin and α/β tubulin in eukaryotes. Here, we describe two novel coiled-coil-rich proteins (CCRPs) in the filament-forming cyanobacterium Anabaena sp. PCC 7120 (hereafter Anabaena) that assemble into a heteropolymer and function in the maintenance of the Anabaena multicellular shape (termed trichome). The two CCRPs - Alr4504 and Alr4505 (named ZicK and ZacK) - are strictly interdependent for the assembly of protein filaments in vivo and polymerize nucleotide independently in vitro, similar to known intermediate filament (IF) proteins. A ΔzicKΔzacK double mutant is characterized by a zigzagged cell arrangement and hence a loss of the typical linear Anabaena trichome shape. ZicK and ZacK interact with themselves, with each other, with the elongasome protein MreB, the septal junction protein SepJ and the divisome associate septal protein SepI. Our results suggest that ZicK and ZacK function in cooperation with SepJ and MreB to stabilize the Anabaena trichome and are likely essential for the manifestation of the multicellular shape in Anabaena. Our study reveals the presence of filament-forming IF-like proteins whose function is achieved through the formation of heteropolymers in cyanobacteria.

Evolution of Homeologous Gene Expression in Polyploid Wheat

Polyploidization has played a prominent role in the evolutionary history of plants. Two recent and sequential allopolyploidization events have resulted in the formation of wheat species with different ploidies, and which provide a model to study the effects of polyploidization on the evolution of gene expression. In this study, we identified differentially expressed genes (DEGs) between four BBAA tetraploid wheats of three different ploidy backgrounds. DEGs were found to be unevenly distributed among functional categories and duplication modes. We observed more DEGs in the extracted tetraploid wheat (ETW) than in natural tetraploid wheats (TD and TTR13) as compared to a synthetic tetraploid (AT2). Furthermore, DEGs showed higher Ka/Ks ratios than those that did not show expression changes (non-DEGs) between genotypes, indicating DEGs and non-DEGs experienced different selection pressures. For A-B homeolog pairs with DEGs, most of them had only one differentially expressed copy, however, when both copies of a homeolog pair were DEGs, the A and B copies were more likely to be regulated to the same direction. Our results suggest that both cis- and inter-subgenome trans-regulatory changes are important drivers in the evolution of homeologous gene expression in polyploid wheat, with ploidy playing a significant role in the process.

Differences in immune components of blood, spleen and head kidney between diploid and auto- and allotriploid Salmonidae

Immune components were investigated in peripheral blood and in spleen and head kidney of autotriploid Salmo trutta f. lacustris, Salvelinus fontinalis, and Salvelinus umbla, and of allotriploid hybrids of S. trutta f. lacustris x Onchorynchus mykiss and S. fontinalis x O. mykiss in comparison to their diploid parents. In peripheral blood the number of lymphocytes was reduced in all investigated autotriploids and in the allotriploid S. trutta f. lacustris x O.mykiss, and the numbers of thrombocytes in autotriploid S. trutta f. lacustris and in both allotriploids. Alternative pathway of complement activity and immunoglobulin concentration were significantly decreased in all investigated auto- and allotriploids, lysozyme activity in autotriploid S. fontinalis and in both allotriploids. In the spleen of the 3 autotriploids the number of erythrocytes was increased, while the number of lymphoid precursor cells was decreased. In their head kidney the erythrocytes numbers were decreased and the numbers of erythropoietic precursor cells and the melanomacrophage centers were increased. Contrary, cytology of spleen and head kidney of the two allotriploid hybrids was similar to diploid controls. Caspase 1, caspase 6, lysozyme, and acid phosphatase activity and immunoglobulin concentration of spleen and head kidney showed specific changes which were related to cytological results. These data indicate alterations in immune system and in lymphoid organs of auto- and allotriploid Salmonidae.

Transcriptome sequencing and histology reveal dosage compensation in the liver of triploid pre-smolt Atlantic salmon

Triploid Atlantic salmon (Salmo salar L.) is seen as one of the best solutions to solve key issues in the salmon farming industry, such as the impact of escapees on wild stocks and pre-harvest sexual maturation. However, the effects of triploidy on salmon smoltification are poorly understood at the molecular level, even though smoltification is a very sensitive period that has a major influence on survival rate and performance of farmed salmon. In this study, we have compared the liver transcriptomes of diploid and triploid Atlantic salmon at three ontogeny stages: fry, parr and smolt. In diploid fish, a total of 2,655 genes were differentially expressed between fry and parr, whereas 506 genes had significantly different transcript levels between parr and smolts. In triploids, 1,507 and 974 genes were differentially expressed between fry and parr, and between parr and smolts, respectively. Most of these genes were down-regulated and 34 genes were differentially expressed between ploidies at the same stage. In both ploidy groups, the top differentially expressed genes with ontogeny stage belonged to common functional categories that can be related to smoltification. Nucleotide and energy metabolism were significantly down-regulated in fry when compared to parr, while immune system processes were significantly down-regulated in parr when compared to smolts. The close resemblance of enriched biological processes and pathways between ploidy groups suggests that triploidy is regulated by genome dosage compensation in Atlantic salmon. Histological analysis revealed that areas of vacuolization (steatosis) were present only in fry and parr stages, in contrast to a compact cellular histology with glycogen granules after smoltification. There was no significant difference in vacuolization between ploidy groups at the fry stage but the liver of diploid parr had a 33.5% higher vacuolization area compared to their triploid counterparts. Taken together, our data provide novel insights into the changes that occur at the molecular and histological level in the liver of both diploid and triploid Atlantic salmon prior to and during smoltification.

Marchantia TCP transcription factor activity correlates with three-dimensional chromatin structure

Information in the genome is not only encoded within sequence or epigenetic modifications, but is also found in how it folds in three-dimensional space. The formation of self-interacting genomic regions, named topologically associated domains (TADs), is known as a key feature of genome organization beyond the nucleosomal level. However, our understanding of the formation and function of TADs in plants is extremely limited. Here we show that the genome of Marchantia polymorpha, a member of a basal land plant lineage, exhibits TADs with epigenetic features similar to those of higher plants. By analysing various epigenetic marks across Marchantia TADs, we find that these regions generally represent interstitial heterochromatin and their borders are enriched with Marchantia transcription factor TCP1. We also identify a type of TAD that we name 'TCP1-rich TAD', in which genomic regions are highly accessible and are densely bound by TCP1 proteins. Transcription of TCP1 target genes differs on the basis gene location, and those in TCP1-rich TADs clearly show a lower expression level. In tcp1 mutant lines, neither TCP1-bound TAD borders nor TCP1-rich TADs display drastically altered chromatin organization patterns, suggesting that, in Marchantia, TCP1 is dispensable for TAD formation. However, we find that in tcp1 mutants, genes residing in TCP1-rich TADs have a greater extent of expression fold change as opposed to genes that do not belong to these TADs. Our results suggest that, besides standing as spatial chromatin-packing modules, plant TADs function as nuclear microcompartments associated with transcription factor activities.

Beyond Synthetic Lethality: Charting the Landscape of Pairwise Gene Expression States Associated with Survival in Cancer

The phenotypic effect of perturbing a gene's activity depends on the activity level of other genes, reflecting the notion that phenotypes are emergent properties of a network of functionally interacting genes. In the context of cancer, contemporary investigations have primarily focused on just one type of functional relationship between two genes-synthetic lethality (SL). Here, we define the more general concept of "survival-associated pairwise gene expression states" (SPAGEs) as gene pairs whose joint expression levels are associated with survival. We describe a data-driven approach called SPAGE-finder that when applied to The Cancer Genome Atlas (TCGA) data identified 71,946 SPAGEs spanning 12 distinct types, only a minority of which are SLs. The detected SPAGEs explain cancer driver genes' tissue specificity and differences in patients' response to drugs and stratify breast cancer tumors into refined subtypes. These results expand the scope of cancer SPAGEs and lay a conceptual basis for future studies of SPAGEs and their translational applications.

Toxinology provides multidirectional and multidimensional opportunities: A personal perspective

In nature, toxins have evolved as weapons to capture and subdue the prey or to counter predators or competitors. When they are inadvertently injected into humans, they cause symptoms ranging from mild discomfort to debilitation and death. Toxinology is the science of studying venoms and toxins that are produced by a wide variety of organisms. In the past, the structure, function and mechanisms of most abundant and/or most toxic components were characterized to understand and to develop strategies to neutralize their toxicity. With recent technical advances, we are able to evaluate and determine the toxin profiles using transcriptomes of venom glands and proteomes of tiny amounts of venom. Enormous amounts of data from these studies have opened tremendous opportunities in many directions of basic and applied research. The lower costs for profiling venoms will further fuel the expansion of toxin database, which in turn will provide greater exciting and bright opportunities in toxin research.

Magnitude of modulation of gene expression in aneuploid maize depends on the extent of genomic imbalance

Aneuploidy has profound effects on an organism, typically more so than polyploidy, and the basis of this contrast is not fully understood. A dosage series of the maize long arm of chromosome 1 (1L) was used to compare relative global gene expression in different types and degrees of aneuploidy to gain insights into how the magnitude of genomic imbalance as well as hypoploidy affects global gene expression. While previously available methods require a selective examination of specific genes, RNA sequencing provides a whole-genome view of gene expression in aneuploids. Most studies of global aneuploidy effects have concentrated on individual types of aneuploids because multiple dose aneuploidies of the same genomic region are difficult to produce in most model genetic organisms. The genetic toolkit of maize allows the examination of multiple ploidies and 1-4 doses of chromosome arms. Thus, a detailed examination of expression changes both on the varied chromosome arms and elsewhere in the genome is possible, in both hypoploids and hyperploids, compared with euploid controls. Previous studies observed the inverse trans effect, in which genes not varied in DNA dosage were expressed in a negative relationship to the varied chromosomal region. This response was also the major type of changes found globally in this study. Many genes varied in dosage showed proportional expression changes, though some were seen to be partly or fully dosage compensated. It was also found that the effects of aneuploidy were progressive, with more severe aneuploids producing effects of greater magnitude.

Genome-Wide Investigation of Heat Shock Transcription Factor Family in Wheat (Triticum aestivum L.) and Possible Roles in Anther Development

Heat shock transcription factors (HSFs) play crucial roles in resisting heat stress and regulating plant development. Recently, HSFs have been shown to play roles in anther development. Thus, investigating the HSF family members and identifying their protective roles in anthers are essential for the further development of male sterile wheat breeding. In the present study, 61 wheat HSF genes (TaHsfs) were identified in the whole wheat genome and they are unequally distributed on 21 chromosomes. According to gene structure and phylogenetic analyses, the 61 TaHsfs were classified into three categories and 12 subclasses. Genome-wide duplication was identified as the main source of the expansion of the wheat HSF gene family based on 14 pairs of homeologous triplets, whereas only a very small number of TaHsfs were derived by segmental duplication and tandem duplication. Heat shock protein 90 (HSP90), HSP70, and another class of chaperone protein called htpG were identified as proteins that interact with wheat HSFs. RNA-seq analysis indicated that TaHsfs have obvious period- and tissue-specific expression patterns, and the TaHsfs in classes A and B respond to heat shock, whereas the C class TaHsfs are involved in drought regulation. qRT-PCR identified three TaHsfA2bs with differential expression in sterile and fertile anthers, and they may be candidate genes involved in anther development. This comprehensive analysis provides novel insights into TaHsfs, and it will be useful for understanding the mechanism of plant fertility conversion.

Identification of Prognostic Dosage-Sensitive Genes in Colorectal Cancer Based on Multi-Omics

Several studies have already identified the prognostic markers in colorectal cancer (CRC) based on somatic copy number alteration (SCNA). However, very little information is available regarding their value as a prognostic marker. Gene dosage effect is one important mechanism of copy number and dosage-sensitive genes are more likely to behave like driver genes. In this work, we propose a new pipeline to identify the dosage-sensitive prognostic genes in CRC. The RNAseq data, the somatic copy number of CRC from TCGA were assayed to screen out the SCNAs. Wilcoxon rank-sum test was used to identify the differentially expressed genes in alteration samples with |SCNA| > 0.3. Cox-regression was used to find the candidate prognostic genes. An iterative algorithm was built to identify the stable prognostic genes. Finally, the Pearson correlation coefficient was calculated between gene expression and SCNA as the dosage effect score. The cell line data from CCLE was used to test the consistency of the dosage effect. The differential co-expression network was built to discover their function in CRC. A total of six amplified genes (NDUFB4, WDR5B, IQCB1, KPNA1, GTF2E1, and SEC22A) were found to be associated with poor prognosis. They demonstrate a stable prognostic classification in more than 50% threshold of SCNA. The average dosage effect score was 0.5918 ± 0.066, 0.5978 ± 0.082 in TCGA and CCLE, respectively. They also show great stability in different data sets. In the differential co-expression network, these six genes have the top degree and are connected to the driver and tumor suppressor genes. Function enrichment analysis revealed that gene NDUFB4 and GTF2E1 affect cancer-related functions such as transmembrane transport and transformation factors. In conclusion, the pipeline for identifying the prognostic dosage-sensitive genes in CRC was proved to be stable and reliable.

Long non-coding RNA GAS5 expression in patients with Down syndrome

Trisomy 21, also known as Down Syndrome (DS), is the most common chromosome abnormality and causes intellectual disability. Long non-coding RNA (lncRNA) growth arrest-specific 5 (GAS5), whose differential expression has recently been reported in patients with Klinefelter syndrome, has been addressed to play a role in the development of inflammatory and autoimmune diseases, vascular endothelial cells apoptosis and atherosclerosis, all being common features in patients with DS. Therefore, the aim of this study was to assess the lncRNA GAS5 expression profile in DS patients and in controls. lncRNA GAS5 levels were evaluated by qRT-PCR assay in 23 patients with DS and 23 age-matched controls. A significant lncRNA GAS5 down-regulation was observed in patients with DS by RT-PCR analysis, The RNA sequencing experiments confirmed the qRT-PCR data. LncRNA GAS5 down-expression may play a role in the development of some typical features of the patients with DS and, particularly, in inflammatory and autoimmune diseases.

The Aquilegia genome reveals a hybrid origin of core eudicots

Background

Whole-genome duplications (WGDs) have dominated the evolutionary history of plants. One consequence of WGD is a dramatic restructuring of the genome as it undergoes diploidization, a process under which deletions and rearrangements of various sizes scramble the genetic material, leading to a repacking of the genome and eventual return to diploidy. Here, we investigate the history of WGD in the columbine genus Aquilegia, a basal eudicot, and use it to illuminate the origins of the core eudicots.

Results

Within-genome synteny confirms that columbines are ancient tetraploids, and comparison with the grape genome reveals that this tetraploidy appears to be shared with the core eudicots. Thus, the ancient gamma hexaploidy found in all core eudicots must have involved a two-step process: first, tetraploidy in the ancestry of all eudicots, then hexaploidy in the ancestry of core eudicots. Furthermore, the precise pattern of synteny sharing suggests that the latter involved allopolyploidization and that core eudicots thus have a hybrid origin.

Conclusions

Novel analyses of synteny sharing together with the well-preserved structure of the columbine genome reveal that the gamma hexaploidy at the root of core eudicots is likely a result of hybridization between a tetraploid and a diploid species.

Synchronized replication of genes encoding the same protein complex in fast-proliferating cells

DNA replication perturbs the dosage balance among genes; at mid-S phase, early-replicating genes have doubled their copies while late-replicating ones have not. Dosage imbalance among genes, especially within members of a protein complex, is toxic to cells. However, the molecular mechanisms that cells use to deal with such imbalance remain not fully understood. Here, we validate at the genomic scale that the dosage between early- and late-replicating genes is imbalanced in HeLa cells. We propose the synchronized replication hypothesis that genes sensitive to stoichiometric relationships will be replicated simultaneously to maintain stoichiometry. In support of this hypothesis, we observe that genes encoding the same protein complex have similar replication timing but mainly in fast-proliferating cells such as embryonic stem cells and cancer cells. We find that the synchronized replication observed in cancer cells, but not in slow-proliferating differentiated cells, is due to convergent evolution during tumorigenesis that restores synchronized replication timing within protein complexes. Taken together, our study reveals that the demand for dosage balance during S phase plays an important role in the optimization of the replication-timing program; this selection is relaxed during differentiation as the cell cycle prolongs and is restored during tumorigenesis as the cell cycle shortens.

Single cell transcriptome in aneuploidies reveals mechanisms of gene dosage imbalance

Aneuploidy is a major source of gene dosage imbalance due to copy number alterations (CNA), and viable human trisomies are model disorders of altered gene expression. We study gene and allele-specific expression (ASE) of 9668 single-cell fibroblasts from trisomy 21 (T21) discordant twins and from mosaic T21, T18, T13 and T8. We examine 928 single cells with deep scRNAseq. Expected and observed overexpression of trisomic genes in trisomic vs. diploid bulk RNAseq is not detectable in trisomic vs. diploid single cells. Instead, for trisomic genes with low-to-average expression, their altered gene dosage is mainly due to the higher fraction of trisomic cells simultaneously expressing these genes, in agreement with a stochastic 2-state burst-like model of transcription. These results, confirmed in a further analysis of 8740 single fibroblasts with shallow scRNAseq, suggest that the specific transcriptional profile of each gene contributes to the phenotypic variability of trisomies. We propose an improved model to understand the effects of CNA and, generally, of gene regulation on gene dosage imbalance.

Transcriptome Profiling Provides Insight into the Genes in Carotenoid Biosynthesis during the Mesocarp and Seed Developmental Stages of Avocado (Persea americana)

Avocado (Persea americana Mill.) is an economically important crop because of its high nutritional value. However, the absence of a sequenced avocado reference genome has hindered investigations of secondary metabolism. For next-generation high-throughput transcriptome sequencing, we obtained 365,615,152 and 348,623,402 clean reads as well as 109.13 and 104.10 Gb of sequencing data for avocado mesocarp and seed, respectively, during five developmental stages. High-quality reads were assembled into 100,837 unigenes with an average length of 847.40 bp (N50 = 1725 bp). Additionally, 16,903 differentially expressed genes (DEGs) were detected, 17 of which were related to carotenoid biosynthesis. The expression levels of most of these 17 DEGs were higher in the mesocarp than in the seed during five developmental stages. In this study, the avocado mesocarp and seed transcriptome were also sequenced using single-molecule long-read sequencing to acquired 25.79 and 17.67 Gb clean data, respectively. We identified 233,014 and 238,219 consensus isoforms in avocado mesocarp and seed, respectively. Furthermore, 104 and 59 isoforms were found to correspond to the putative 11 carotenoid biosynthetic-related genes in the avocado mesocarp and seed, respectively. The isoform numbers of 10 out of the putative 11 genes involved in the carotenoid biosynthetic pathway were higher in the mesocarp than those in the seed. Besides, alpha- and beta-carotene contents in the avocado mesocarp and seed during five developmental stages were also measured, and they were higher in the mesocarp than in the seed, which validated the results of transcriptome profiling. Gene expression changes and the associated variations in gene dosage could influence carotenoid biosynthesis. These results will help to further elucidate carotenoid biosynthesis in avocado.

A comprehensive genomic scan reveals gene dosage balance impacts on quantitative traits in Populus trees

Gene dosage variation and the associated changes in gene expression influence a wide variety of traits, ranging from cancer in humans to yield in plants. It is also expected to affect important traits of ecological and agronomic importance in forest trees, but this variation has not been systematically characterized or exploited. Here we performed a comprehensive scan of the Populus genome for dosage-sensitive loci affecting quantitative trait variation for spring and fall phenology and biomass production. The study population was a large collection of clonally propagated F1 hybrid lines of Populus that saturate the genome 10-fold with deletions and insertions (indels) of known sizes and positions. As a group, the phenotypic means of the indel lines consistently differed from control nonindel lines, with an overall negative effect of both insertions and deletions on all biomass-related traits but more diverse effects and an overall wider phenotypic distribution of the indel lines for the phenology-related traits. We also investigated the correlation between gene dosage at specific chromosomal locations and phenotype, to identify dosage quantitative trait loci (dQTL). Such dQTL were detected for most phenotypes examined, but stronger effect dQTL were identified for the phenology-related traits than for the biomass traits. Our genome-wide screen for dosage sensitivity in a higher eukaryote demonstrates the importance of global genomic balance and the impact of dosage on life history traits.