Karyotyping of aneuploid and polyploid plants from low coverage whole-genome resequencing.

BACKGROUND: Karyotype, as a basic characteristic of species, provides valuable information for fundamental theoretical research and germplasm resource innovation. However, traditional karyotyping techniques, including fluorescence in situ hybridization (FISH), are challenging and low in efficiency, especially when karyotyping aneuploid and polyploid plants. The use of low coverage whole-genome resequencing (lcWGR) data for karyotyping was explored, but existing methods are complicated and require control samples. RESULTS: In this study, a new protocol for molecular karyotype analysis was provided, which proved to be a simpler, faster, and more accurate method, requiring no control. Notably, our method not only provided the copy number of each chromosome of an individual but also an accurate evaluation of the genomic contribution from its parents. Moreover, we verified the method through FISH and published resequencing data. CONCLUSIONS: This method is of great significance for species evolution analysis, chromosome engineering, crop improvement, and breeding.

Downregulation of the expression of subgenomic chromosome A7 genes promotes plant height in resynthesized allopolyploid Brassica napus.

KEY MESSAGE: Homoeolog expression bias and the gene dosage effect induce downregulation of genes on chromosome A7, causing a significant increase in the plant height of resynthesized allopolyploid Brassica napus. Gene expression levels in allopolyploid plants are not equivalent to the simple average of the expression levels in the parents and are associated with several non-additive expression phenomena, including homoeolog expression bias. However, hardly any information is available on the effect of homoeolog expression bias on traits. Here, we studied the effects of gene expression-related characteristics on agronomic traits using six isogenic resynthesized Brassica napus lines across the first ten generations. We found a group of genes located on chromosome A7 whose expression levels were significantly negatively correlated with plant height. They were expressed at significantly lower levels than their homoeologous genes, owing to allopolyploidy rather than inheritance from parents. Homoeolog expression bias resulted in resynthesized allopolyploids with a plant height similar to their female Brassica oleracea parent, but significantly higher than that of the male Brassica rapa parent. Notably, aneuploid lines carrying monosomic and trisomic chromosome A7 had the highest and lowest plant heights, respectively, due to changes in the expression bias of homoeologous genes because of alterations in the gene dosage. These findings suggest that the downregulation of the expression of homoeologous genes on a single chromosome can result in the partial improvement of traits to a significant extent in the nascent allopolyploid B. napus.

Genome balance and dosage effect drive allopolyploid formation in Brassica.

Polyploidy is a major evolutionary force that has shaped plant diversity. However, the various pathways toward polyploid formation and interploidy gene flow remain poorly understood. Here, we demonstrated that the immediate progeny of allotriploid AAC Brassica (obtained by crossing allotetraploid Brassica napus and diploid Brassica rapa) was predominantly aneuploids with ploidal levels ranging from near-triploidy to near-hexaploidy, and their chromosome numbers deviated from the theoretical distribution toward increasing chromosome numbers, suggesting that they underwent selection. Karyotype and phenotype analyses showed that aneuploid individuals containing fewer imbalanced chromosomes had higher viability and fertility. Within three generations of self-fertilization, allotriploids mainly developed into near or complete allotetraploids similar to B. napus via gradually increasing chromosome numbers and fertility, suggesting that allotriploids could act as a bridge in polyploid formation, with aneuploids as intermediates. Self-fertilized interploidy hybrids ultimately generated new allopolyploids carrying different chromosome combinations, which may create a reproductive barrier preventing allotetraploidy back to diploidy and promote gene flow from diploids to allotetraploids. These results suggest that the maintenance of a proper genome balance and dosage drove the recurrent conversion of allotriploids to allotetraploids, which may contribute to the formation and evolution of polyploids.

Incomplete genome doubling enables to consistently enhance plant growth for maximum biomass production by altering multiple transcript co-expression networks in potato.

KEY MESSAGE: Cytochimera potato plants, which mixed with diploid and tetraploid cells, could cause the highest and significantly increased biomass yield than the polyploid and diploid potato plants. Polyploidization is an important approach in crop breeding for agronomic trait improvement, especially for biomass production. Cytochimera contains two or more mixed cells with different levels of ploidy, which is considered a failure in whole genome duplication. Using colchicine treatment with diploid (Dip) potato (Solanum chacoense) plantlets, this study generated tetraploid (Tet) and cytochimera (Cyt) lines, which, respectively, contained complete and partial cells with genome duplication. Compared to the Dip potato, we observed remarkably enhanced plant growth and biomass yields in Tet and Cyt lines. Notably, the Cyt potato straw, which was generated from incomplete genome doubling, was of significantly higher biomass yield than that of the Tet with a distinctively altered cell wall composition. Meanwhile, we observed that one layer of the tetraploid cells (about 30%) in Cyt plants was sufficient to trigger a gene expression pattern similar to that of Tet, suggesting that the biomass dominance of Cyt may be related to the proportion of different ploidy cells. Further genome-wide analyses of co-expression networks indicated that down-regulation (against Dip) of spliceosomal-related transcripts might lead to differential alternative splicing for specifically improved agronomic traits such as plant growth, biomass yield, and lignocellulose composition in Tet and Cyt plants. In addition, this work examined that the genome of Cyt line was relatively stable after years of asexual reproduction. Hence, this study has demonstrated that incomplete genome doubling is a promising strategy to maximize biomass production in potatoes and beyond.

Modified lignocellulose and rich starch for complete saccharification to maximize bioethanol in distinct polyploidy potato straw.

Potato is a major food crop with enormous biomass straw, but lignocellulose recalcitrance causes a costly bioethanol conversion. Here, we selected the cytochimera (Cyt) potato samples showing significantly-modified lignocellulose and much increased soluble sugars and starch by 2-4 folds in mature straws. Under two pretreatments (8 min liquid hot water; 5% CaO) at minimized conditions, the potato Cyt straw showed complete enzymatic saccharification. Further performing yeast fermentation with all hexoses released from soluble sugars, starch and lignocellulose in the Cyt straw, this study achieved a maximum bioethanol yield of 24 % (% dry matter), being higher than those of other bioenergy crops as previously reported. Hence, this study has proposed a novel mechanism model on the reduction of major lignocellulose recalcitrance and regulation of carbon assimilation to achieve cost-effective bioethanol production under optimal pretreatments. This work also provides a sustainable strategy for utilization of potato straws with minimum waste release.

Chromosome inheritance and meiotic stability in allopolyploid Brassica napus.

Homoeologous recombination, aneuploidy, and other genetic changes are common in resynthesized allopolyploid Brassica napus. In contrast, the chromosomes of cultivars have long been considered to be meiotically stable. To gain a better understanding of the underlying mechanisms leading to stabilization in the allopolyploid, the behavior of chromosomes during meiosis can be compared by unambiguous chromosome identification between resynthesized and natural B. napus. Compared with natural B. napus, resynthesized lines show high rates of nonhomologous centromere association, homoeologous recombination leading to translocation, homoeologous chromosome replacement, and association and breakage of 45S rDNA loci. In both natural and resynthesized B. napus, we observed low rates of univalents, A-C bivalents, and early sister chromatid separations. Reciprocal homoeologous chromosome exchanges and double reductions were photographed for the first time in meiotic telophase I. Meiotic errors were non-uniformly distributed across the genome in resynthesized B. napus, and in particular homoeologs sharing synteny along their entire length exhibited multivalents at diakinesis and polysomic inheritance at telophase I. Natural B. napus appeared to resolve meiotic errors mainly by suppressing homoeologous pairing, resolving nonhomologous centromere associations and 45S rDNA associations before diakinesis, and reducing homoeologous cross-overs.

Metabolic characteristics of obese children with fatty liver: A STROBE-compliant article.

To investigate metabolic differences between simple obese children and those comorbid with fatty liver disease.Obese children hospitalized in our center from 2014 to 2016 were included and divided into simple obese group and obese with fatty liver group by ultrasound-based diagnosis of fatty liver. Epidemiology data and serum biochemical studies were recorded. Body Mass Index (BMI) and homeostasis model insulin resistance index (HOMA-IR) were calculated accordingly.A total of 186 obese children were enrolled in this study, including 93 cases of obese children and 93 obese patients' comorbid with fatty liver. The proportion of male, age, waist circumference (WC), BMI, fasting blood-glucose (FBG), glycosylated hemoglobin A1c (HbA1c), fasting insulin (FINS), and HOMA-IR were significantly higher in obese patients with fatty liver (P <.05). Age and BMI were found to be independent risk factors for fatty liver disease (OR >1, P <.05).Among obese children, male and elder patients and individuals with higher uric acid are more susceptible to fatty liver.

Reconstruction of evolutionary trajectories of chromosomes unraveled independent genomic repatterning between Triticeae and Brachypodium.

BACKGROUND: After polyploidization, a genome may experience large-scale genome-repatterning, featuring wide-spread DNA rearrangement and loss, and often chromosome number reduction. Grasses share a common tetraploidization, after which the originally doubled chromosome numbers reduced to different chromosome numbers among them. A telomere-centric reduction model was proposed previously to explain chromosome number reduction. With Brachpodium as an intermediate linking different major lineages of grasses and a model plant of the Pooideae plants, we wonder whether it mediated the evolution from ancestral grass karyotype to Triticeae karyotype. RESULTS: By inferring the homology among Triticeae, rice, and Brachpodium chromosomes, we reconstructed the evolutionary trajectories of the Triticeae chromosomes. By performing comparative genomics analysis with rice as a reference, we reconstructed the evolutionary trajectories of Pooideae plants, including Ae. Tauschii (2n = 14, DD), barley (2n = 14), Triticum turgidum (2n = 4x = 28, AABB), and Brachypodium (2n = 10). Their extant Pooidea and Brachypodium chromosomes were independently produced after sequential nested chromosome fusions in the last tens of millions of years, respectively, after their split from rice. More frequently than would be expected by chance, in Brachypodium, the 'invading' and 'invaded' chromosomes are homoeologs, originating from duplication of a common ancestral chromosome, that is, with more extensive DNA-level correspondence to one another than random chromosomes, nested chromosome fusion events between homoeologs account for three of seven cases in Brachypodium (P-value≈0.00078). However, this phenomenon was not observed during the formation of other Pooideae chromosomes. CONCLUSIONS: Notably, we found that the Brachypodium chromosomes formed through exclusively distinctive trajectories from those of Pooideae plants, and were well explained by the telomere-centric model. Our work will contribute to understanding the structural and functional innovation of chromosomes in different Pooideae lineages and beyond.

Genomic, expressional, protein-protein interactional analysis of Trihelix transcription factor genes in Setaria italia and inference of their evolutionary trajectory.

BACKGROUND: Trihelix transcription factors (TTF) play important roles in plant growth and response to adversity stress. Until now, genome-wide identification and analysis of this gene family in foxtail millet has not been available. Here, we identified TTF genes in the foxtail millet and its grass relatives, and characterized their functional domains. RESULTS: As to sequence divergence, TTF genes were previously divided into five subfamilies, I-V. We found that Trihelix family members in foxtail millet and other grasses mostly preserved their ancestral chromosomal locations during millions of years' evolution. Six amino acid sites of the SIP1 subfamily possibly were likely subjected to significant positive selection. Highest expression level was observed in the spica, with the SIP1 subfamily having highest expression level. As to the origination and expansion of the gene family, notably we showed that a subgroup of subfamily IV was the oldest, and therefore was separated to define a new subfamily O. Overtime, starting from the subfamily O, certain genes evolved to form subfamilies III and I, and later from subfamily I to develop subfamilies II and V. The oldest gene, Si1g016284, has the most structural changes, and a high expression in different tissues. What's more interesting is that it may have bridge the interaction with different proteins. CONCLUSIONS: By performing phylogenetic analysis using non-plant species, notably we showed that a subgroup of subfamily IV was the oldest, and therefore was separated to define a new subfamily O. Starting from the subfamily O, certain genes evolved to form other subfamilies. Our work will contribute to understanding the structural and functional innovation of Trihelix transcription factor, and the evolutionary trajectory.