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Phylogenetic Analysis of Different Ploidy Saccharum spontaneum Based on rDNA-ITS Sequences.

ABSTRACT: Saccharum spontaneum L. is a crucial wild parent of modern sugarcane cultivars whose ploidy clones have been utilized successfully in improving the stress resistance and yield related traits of sugarcane cultivars. To establish knowledge regarding the genetic variances and evolutional relationships of ploidy clones of Saccharum spontaneum collected in China, the rDNA-ITS sequences of 62 ploidy clones including octaploid clones (2n = 64), nonaploid clones (2n = 72), decaploid clones (2n = 80), and dodecaploid clones (2n = 96), were obtained and analyzed. The rDNA-ITS sequences of four species from Saccharum and Sorghum bicolor selected as controls. The results showed that decaploid clones (2n = 80) possess the most abundant variances with 58 variable sites and 20 parsim-informative sites in ITS sequences, which were then followed by octaploid clones with 43 variable sites and 17 parsim-informative sites. In haplotype diversity, all four population exhibited high diversity, especially nonaploid and decaploid populations. By comparing the genetic distances among four ploidy populations, the dodecaploid population exhibited the closest relationship with the nonaploid population, and then the relationship strength decreased successively for the decaploid population and then for the octaploid population. Population differentiation analysis showed that the phenomena of population differentiation were not found among different ploidy populations, and low coefficient of gene differentiation(Gst) and high gene flow(Nm) occur among these populations possessing close genetic relationship. These results mentioned above will contribute to the understanding of the evolution of different ploidy populations of Saccharum spontaneum and provide vital knowledge for their utilization in sugarcane breeding and innovation.

SUBMITTER: Liu X

PROVIDER: S-EPMC4795546 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Phylogenetic Analysis of Different Ploidy Saccharum spontaneum Based on rDNA-ITS Sequences.

Liu Xinlong X Li Xujuan X Liu Hongbo H Xu Chaohua C Lin Xiuqin X Li Chunjia C Deng Zuhu Z

PloS one 20160317 3

Saccharum spontaneum L. is a crucial wild parent of modern sugarcane cultivars whose ploidy clones have been utilized successfully in improving the stress resistance and yield related traits of sugarcane cultivars. To establish knowledge regarding the genetic variances and evolutional relationships of ploidy clones of Saccharum spontaneum collected in China, the rDNA-ITS sequences of 62 ploidy clones including octaploid clones (2n = 64), nonaploid clones (2n = 72), decaploid clones (2n = 80), an ...[more]

PMID: 26986847

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Project description:Sugarcane (Saccharum spp. hybrids) is an economically important crop widely grown in tropical and subtropical regions for sugar and ethanol production. However, the large genome size, high ploidy level, interspecific hybridization and aneuploidy make sugarcane one of the most complex genomes and have long hampered genome research in sugarcane. Modern sugarcane cultivars are derived from interspecific hybridization between S. officinarum and S. spontaneum with 80-90% of the genome from S. officinarum and 10-20% of the genome from S. spontaneum. We constructed bacterial artificial chromosome (BAC) libraries of S. officinarum variety LA Purple (2n = 8x = 80) and S. spontaneum haploid clone AP85-441 (2n = 4x = 32), and selected and sequenced 97 BAC clones from the two Saccharum BAC libraries. A total of 5,847,280 bp sequence from S. officinarum and 5,011,570 bp from S. spontaneum were assembled and 749 gene models were annotated in these BACs. A relatively higher gene density and lower repeat content were observed in S. spontaneum BACs than in S. officinarum BACs. Comparative analysis of syntenic regions revealed a high degree of collinearity in genic regions between Saccharum and Sorghum bicolor and between S. officinarum and S. spontaneum. In the syntenic regions, S. spontaneum showed expansion relative to S. officinarum, and both S. officinarum and S. spontaneum showed expansion relative to sorghum. Among the 75 full-length LTR retrotransposons identified in the Saccharum BACs, none of them are older than 2.6 mys and no full-length LTR elements are shared between S. officinarum and S. spontaneum. In addition, divergence time estimated using a LTR junction marker and a syntenic gene shared by 3 S. officinarum and 1 S. spontaneum BACs revealed that the S. spontaneum intergenic region was distant to those from the 3 homologous regions in S. officinarum. Our results suggested that S. officinarum and S. spontaneum experienced at least two rounds of independent polyploidization in each lineage after their divergence from a common ancestor.

Project description:BACKGROUND:Sucrose phosphate synthase (SPS) genes play vital roles in sucrose production across various plant species. Modern sugarcane cultivar is derived from the hybridization between the high sugar content species Saccharum officinarum and the high stress tolerance species Saccharum spontaneum, generating one of the most complex genomes among all crops. The genomics of sugarcane SPS remains under-studied despite its profound impact on sugar yield. RESULTS:In the present study, 8 and 6 gene sequences for SPS were identified from the BAC libraries of S. officinarum and S. spontaneum, respectively. Phylogenetic analysis showed that SPSD was newly evolved in the lineage of Poaceae species with recently duplicated genes emerging from the SPSA clade. Molecular evolution analysis based on Ka/Ks ratios suggested that polyploidy reduced the selection pressure of SPS genes in Saccharum species. To explore the potential gene functions, the SPS expression patterns were analyzed based on RNA-seq and proteome dataset, and the sugar content was detected using metabolomics analysis. All the SPS members presented the trend of increasing expression in the sink-source transition along the developmental gradient of leaves, suggesting that the SPSs are involved in the photosynthesis in both Saccharum species as their function in dicots. Moreover, SPSs showed the higher expression in S. spontaneum and presented expressional preference between stem (SPSA) and leaf (SPSB) tissue, speculating they might be involved in the differentia of carbohydrate metabolism in these two Saccharum species, which required further verification from experiments. CONCLUSIONS:SPSA and SPSB genes presented relatively high expression and differential expression patterns between the two Saccharum species, indicating these two SPSs are important in the formation of regulatory networks and sucrose traits in the two Saccharum species. SPSB was suggested to be a major contributor to the sugar accumulation because it presented the highest expressional level and its expression positively correlated with sugar content. The recently duplicated SPSD2 presented divergent expression levels between the two Saccharum species and the relative protein content levels were highest in stem, supporting the neofunctionalization of the SPSD subfamily in Saccharum.

Project description:Polyploid Saccharum with complex genomes hindered the progress of sugarcane improvement, while their chloroplast genomes are much smaller and simpler. Chloroplast (cp), the vital organelle, is the site of plant photosynthesis, which also evolves other functions, such as tolerance to environmental stresses. In this study, the cp genome of two sugarcane ancestors Saccharum officinarum and S. spontaneum were sequenced, and genome comparative analysis between these two species was carried out, together with the photosynthetic ability. The length is 141,187 bp for S. officinarum and that is 7 bp longer than S. spontaneum, with the same GC content (38.44%) and annotated gene number (134), 13 with introns among them. There is a typical tetrad structure, including LSC, SSC, IRb and IRa. Of them, LSC and IRa/IRb are 18 bp longer and 6 bp shorter than those in S. spontaneum (83,047 bp and 22,795 bp), respectively, while the size of SSC is same (12,544 bp). Five genes exhibit contraction and expansion at the IR junctions, but only one gene ndhF with 29 bp expansion at the border of IRb/SSC. Nucleotide diversity (Pi) based on sliding window analysis showed that the single copy and noncoding regions were more divergent than IR- and coding regions, and the variant hotspots trnG-trnM, psbM-petN, trnR-rps14, ndhC-trnV and petA-psbJ in the LSC and trnL-ccsA in the SSC regions were detected, and petA-psbJ with the highest divergent value of 0.01500. Genetic distances of 65 protein genes vary from 0.00000 to 0.00288 between two species, and the selective pressure on them indicated that only petB was subjected to positive selection, while more genes including rpoC2, rps3, ccsA, ndhA, ndhA, psbI, atpH and psaC were subjected to purifying or very strong purifying selection. There are larger number of codons in S. spontaneum than that in S. officinarum, while both species have obvious codon preference and the codons with highest-(AUG) and lowest frequency (AUA) are same. Whilst, the most abundant amino acid is leucine in both S. officinarum and S. spontaneum, with number of 2175 (10.88% of total) and 2228 (10.90% of total) codons, respectively, and the lowest number is cysteine, with only 221 (1.105%) and 224 (1.096%), respectively. Protein collinearity analysis showed the high collinearity though several divergences were present in cp genomes, and identification of simple sequence repeats (SSRs) were included in this study. In addition, in order to compare cold tolerance and explore the expanding function of this environmental stress, the chlorophyll relative content (SPAD) and chlorophyll fluorescence Fv/Fm were measured. The significantly higher SPAD were observed in S. spontaneum than those in S. officinarum, no matter what the control conditions, exposure to low temperature or during recovery, and so was for Fv/Fm under exposure to low temperature, together with higher level of SPAD in S. spontaneum in each measurement. Aforementioned results suggest much stronger photosynthetic ability and cold tolerance in S. spontaneum. Our findings build a foundation to investigate the biological mechanism of two sugarcane ancestor chloroplasts and retrieve reliable molecular resources for phylogenetic and evolutionary studies, and will be conducive to genetic improvement of photosynthetic ability and cold resistance in modern sugarcane.

Project description:BackgroundThe genus Arachis comprises 80 species and it is subdivided into nine taxonomic sections (Arachis, Caulorrhizae, Erectoides, Extranervosae, Heteranthae, Procumbentes, Rhizomatosae, Trierectoides, and Triseminatae). This genus is naturally confined to South America and most of its species are native to Brazil. In order to provide a better understanding of the evolution of the genus, we reconstructed the phylogeny of 45 species using the variation observed on nucleotide sequences in internal transcribed spacer regions (ITS1 and ITS2) and 5.8 S of nuclear ribosomal DNA.ResultsIntraspecific variation was detected, but in general it was not enough to place accessions of the same species in different clades. Our data support the view that Arachis is a monophyletic group and suggested Heteranthae as the most primitive section of genus Arachis. The results confirmed the circumscriptions of some sections (Caulorrhizae, Extranervosae), but raised questions about others. Sections Erectoides, Trierectoides and Procumbentes were not well defined, while sections Arachis and Rhizomatosae seem to include species that could be moved to different sections. The division of section Arachis into A and B genome species was also observed in the phylogenetic tree and these two groups of species may not have a monophyletic origin. The 2n = 2x = 18 species of section Arachis (A. praecox, A. palustris and A. decora) were all placed in the same clade, indicating they are closely related to each other, and their genomes are more related to B genome than to the A genome. Data also allowed insights on the origin of tetraploid A. glabrata, suggesting rhizome appeared twice within the genus and raising questions about the placement of that species in section Rhizomatosae.ConclusionThe main clades established in this study in general agreed with many other studies that have used other types of evidences and sets of species, being some of them included in our study and some not. Thus, the relationships established can be a useful framework for future systematic reviews of genus Arachis and for the selection of species to pre-breeding programs.

Project description:BackgroundSugarcane is a major sugar and biofuel crop, but genomic research and molecular breeding have lagged behind other major crops due to the complexity of auto-allopolyploid genomes. Sugarcane cultivars are frequently aneuploid with chromosome number ranging from 100 to 130, consisting of 70-80 % S. officinarum, 10-20 % S. spontaneum, and 10 % recombinants between these two species. Analysis of a genomic region in the progenitor autoploid genomes of sugarcane hybrid cultivars will reveal the nature and divergence of homologous chromosomes.ResultsTo investigate the origin and evolution of haplotypes in the Bru1 genomic regions in sugarcane cultivars, we identified two BAC clones from S. spontaneum and four from S. officinarum and compared to seven haplotype sequences from sugarcane hybrid R570. The results clarified the origin of seven homologous haplotypes in R570, four haplotypes originated from S. officinarum, two from S. spontaneum and one recombinant.. Retrotransposon insertions and sequences variations among the homologous haplotypes sequence divergence ranged from 18.2 % to 60.5 % with an average of 33.7 %. Gene content and gene structure were relatively well conserved among the homologous haplotypes. Exon splitting occurred in haplotypes of the hybrid genome but not in its progenitor genomes. Tajima's D analysis revealed that S. spontaneum hapotypes in the Bru1 genomic regions were under strong directional selection. Numerous inversions, deletions, insertions and translocations were found between haplotypes within each genome.ConclusionsThis is the first comparison among haplotypes of a modern sugarcane hybrid and its two progenitors. Tajima's D results emphasized the crucial role of this fungal disease resistance gene for enhancing the fitness of this species and indicating that the brown rust resistance gene in R570 is from S. spontaneum. Species-specific InDel, sequences similarity and phylogenetic analysis of homologous genes can be used for identifying the origin of S. spontaneum and S. officinarum haplotype in Saccharum hybrids. Comparison of exon splitting among the homologous haplotypes suggested that the genome rearrangements in Saccharum hybrids after hybridization. The combined minimum difference at 19.5 % among homologous chromosomes in S. officinarum would be sufficient for proper genome assembly of this autopolyploid genome. Retrotransposon insertions and sequences variations among the homologous haplotypes sequence divergence may allow sequencing and assembling the autopolyploid Saccharum genomes and the auto-allopolyploid hybrid genomes using whole genome shotgun sequencing.

Dataset Information

Phylogenetic Analysis of Different Ploidy Saccharum spontaneum Based on rDNA-ITS Sequences.

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Phylogenetic Analysis of Different Ploidy Saccharum spontaneum Based on rDNA-ITS Sequences.

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