Variation In Nuclear DNA Content Research Articles

Divergence of 10 satellite repeats in Artemisia (Asteraceae: Anthemideae) based on sequential fluorescence in situ hybridization analysis: evidence for species identification and evolution.

Artemisia is a large genus encompassing about 400 diverse species, many of which have considerable medicinal and ecological value. However, complex morphological information and variation in ploidy level and nuclear DNA content have presented challenges for evolution studies of this genus. Consequently, taxonomic inconsistencies within the genus persist, hindering the utilization of such large plant resources. Researchers have utilized satellite DNAs to aid in chromosome identification, species classification, and evolutionary studies due to their significant sequence and copy number variation between species and close relatives. In the present study, the RepeatExplorer2 pipeline was utilized to identify 10 satellite DNAs from three species (Artemisia annua, Artemisia vulgaris, Artemisia viridisquama), and fluorescence in situ hybridization confirmed their distribution on chromosomes in 24 species, including 19 Artemisia species with 5 outgroup species from Ajania and Chrysanthemum. Signals of satellite DNAs exhibited substantial differences between species. We obtained one genus-specific satellite from the sequences. Additionally, molecular cytogenetic maps were constructed for Artemisia vulgaris, Artemisia leucophylla, and Artemisia viridisquama. One species (Artemisia verbenacea) showed a FISH distribution pattern suggestive of an allotriploid origin. Heteromorphic FISH signals between homologous chromosomes in Artemisia plants were observed at a high level. Additionally, the relative relationships between species were discussed by comparing ideograms. The results of the present study provide new insights into the accurate identification and taxonomy of the Artemisia genus using molecular cytological methods.

Discovery and Characterization of Novel Fertile Triploids and a New Chromosome Number in Caladium (Caladium × hortulanum)

Cultivated caladium (Caladium × hortulanum; 2n = 2x = 30) is an important ornamental aroid for the environmental horticulture industry. A better understanding of its genetic diversity is needed for continued improvement of caladium. The caladium germplasm maintained in the University of Florida’s caladium breeding program were surveyed for potential variation in chromosome number and nuclear DNA content to gain a better understanding of caladium genetic diversity at the cytogenetic level. For the first time caladium triploidy was discovered in two breeding lines, UF-15-414 and UF-4407 with 2n = 3x = 45 chromosomes and a nuclear DNA content of 13.86 pg·2C−1. In addition, a new chromosome number (2n = 2x = 34) was found in one cultivar, ‘White Wing’. Compared with their diploid parents or grandparents, the triploids showed a distinct, attractive leaf morphology with rounder and thicker leaves. The pollen stainability of UF-15-414 and UF-4407 was 63% and 73%, respectively, indicating potential male fertility, which was unexpected. Analysis of simple sequence repeat (SSR) marker banding patterns confirmed that UF-15-414 was a direct progeny of UF-4407 through hybridization with the diploid cultivar Aaron, whereas UF-4407 might result from fusion of an unreduced (female or male) gamete with a reduced gamete. Chromosome counting and SSR marker analysis of ‘White Wing’ and its progeny cultivars ‘White Wonder’ and ‘White Delight’ suggested that ‘White Wing’ possibly transmitted its 34 chromosomes to progeny during sexual reproduction. The discovery and characterization of these triploids revealed the occurrence of natural sexual polyploidization in caladium and indicated good potential for creating and selecting new triploids for future caladium breeding. The observed new chromosome number in ‘White Wing’ and its progeny cultivars implies that other chromosome variations may be present among cultivated caladiums. In summary, these results revealed two male-fertile triploid caladiums and a new chromosome number that can enrich the cytogenetic diversity in future caladium cultivar development.

Genetic and nuclear DNA content variation of stevia (Stevia rebaudiana Bertoni) accessions grown in Turkey

The objectives of this study were to make morphological and molecular characterization of Turkish stevia accessions. The field data showed significant variations (P < 0.05) for all morphological parameters (plant height, number of main stems per plant, number of secondary stems, fresh and herb yields) exception with number of secondary stems. The primers of MtP5CS, AtNHX1, MtProDH, Mt-Actin MtSOS1and MtSOS2 genes were used as loci specific DNA markers. All markers were amplified in Stevia genome and provided a mean of 74.16% polymorphism rate. Flow cytometer analysis showed no statistically significant differences (P < 0.16) for 2C DNA content with a mean of 1.62 pg. The UPGMA analysis revealed that Samsun accession was distinctly separated from the others and had the lowest 2C DNA content (1.52 pg). This study first time showed that the stevia accessions grown in Turkey have limited genetic and no nuclear DNA content variations. The results also revealed that gene targeted functional markers associated with salt and drought tolerance have a great potential to be used as DNA markers to determine the genetic variation in plants

Nuclear DNA Content Variation in Different Life Cycle Stages of Sugar Kelp, Saccharina latissima

Ploidy variants can be utilized to increase yield, introduce sterility, and modify specific traits with an economic impact. Despite economic importance of Saccharina species, their nuclear DNA content in different cell types and life stages remain unclear. The present research was initiated to determine the nuclear DNA content and intraindividual variation at different life cycle stages of the Laminarialean kelp Saccharina latissima. Nuclear DNA content in embryonic and mature sporophytes, released and unreleased zoospores, female, and male gametophytes from Sør-Trøndelag county in Norway were estimated by image analysis using the DNA-localizing fluorochrome DAPI and chicken’s red blood cells as a standard. DNA content of a total of 6905 DAPI-stained nuclei was estimated. This is the first study of nuclear DNA content which covered the life cycle of kelp. The lowest level of DNA content (1C) was observed in zoospores with an average of 0.76 pg. Male and female single spore gametophyte cultures presented higher average DNA content, more than double that of zoospores, suggesting the presence of polyteny. Female gametophyte nuclei were slightly larger and more variable in size than those of male gametophytes. The DNA content observed in embryonic sporophytes and in meristoderm cells from older sporophytes (1.51 pg) was 2C as expected and in the range of previously published studies of sporophytes of S. latissima. Mature sporophytes showed intra-plant variation with DNA content values ranging from 2-16C. The main difference was between meristoderm cells (mostly 2C) and cortical and medullary cells (2-16C).

Karyological and nuclear DNA content variation of the genus Asparagus.

Asparagus wild relatives could be a promising possibility to extent the genetic variability of garden asparagus and for new cultivars with favorable traits such as high yield stability, disease resistance and stress tolerance. In order to achieve an efficient use in breeding, a detailed cytogenetic characterization of the accessions is necessary. This study worked on 35 Asparagus accessions, including A. officinalis cultivars (‘Darlise’, ‘Ravel’ and ‘Steiners Violetta’) and Asparagus wild relatives, for which the number of chromosomes, their size, the nuclear DNA content, and the genomic distribution of 5S and 45S rDNA were analyzed. Different ploidy levels (diploid, triploid, tetraploid, pentaploid and hexaploid) were found. Furthermore, the size of the chromosomes of all diploid Asparagus accessions was determined which led to differences in the karyotypic formula. A. plocamoides harbors the smallest chromosome with 1.21 μm, whereas the largest chromosome with 5.43 μm was found in A. officinalis. In all accessions one 5S rDNA locus per genome was observed, while the number of 45S rDNA loci varied between one (A. albus, A. plumosus, A. stipularis) to four (A. setaceus). In most Asparagus accessions, the 5S and 45S rDNA signals were located on different chromosomes. In contrast, the genomes of A. africanus, A. plocamoides, A. sp. (a taxonomically unclassified Asparagus species from Asia) and A. verticillatus (diploid accessions) have one 5S and one 45S rDNA signal on the same chromosome. The measured 2C DNA content ranges from 1.43 pg (A. plocamoides, diploid) to 8.24 pg (A. amarus, hexaploid). Intraspecific variations for chromosome number, karyotypic formula, signal pattern with 5S and 45s rDNA probes and DNA content were observed. Interspecific variations were also recognized in the genus Asparagus.

Integration of Genotoxic Biomarkers in Environmental Biomonitoring Analysis Using a Multi-Biomarker Approach in Three-Spined Stickleback (Gasterosteus aculeatus Linnaeus, 1758).

Water is impacted by a variety of increasing pressures, such as contaminants, including genotoxic pollutants. The proposed multi-biomarker approach at a sub-individual level gives a complementary indicator to the chemical and ecological parameters of the Water Framework Directive (WFD, 2000/60/EC). By integrating biomarkers of genotoxicity and erythrocyte necrosis in the sentinel fish species the three-spined stickleback (Gasterosteus aculeatus) through active biomonitoring of six stations of the Artois-Picardie watershed, north France, our work aimed to improve the already existing biomarker approach. Even if fish in all stations had high levels of DNA strand breaks, the multivariate analysis (PCA), followed by hierarchical agglomerative clustering (HAC), improved discrimination among stations by detecting an increase of nuclear DNA content variation (Etaing, St Rémy du Nord, Artres and Biache-St-Vaast) and erythrocyte necrosis (Etaing, St Rémy du Nord). The present work highlighted that the integration of these biomarkers of genotoxicity in a multi-biomarker approach is appropriate to expand physiological parameters which allow the targeting of new potential effects of contaminants.

Lack of variation in nuclear DNA content in avian muscle.

The avian pectoralis muscle demonstrates plasticity with regard to size, so that temperate birds facing winter conditions or birds enduring a migration bout tend to have significant increases in the size and mass of this tissue due to muscular hypertrophy. Myonuclear domain (MND), the volume of cytoplasm a myonuclei services, in the pectoralis muscle of birds seems to be altered during thermal stress or changing seasons. However, there is no information available regarding muscle DNA content or ploidy level within the avian pectoralis. Changes in muscle DNA content can be used in this tissue to aid in size and mass changes. Here, we hypothesized that long-distance migrants or temperate residents would use the process of endoreduplication to aid in altering muscle size. Mostly contradictory to our hypotheses, we found no differences in the mean muscle DNA content in any of the 62 species of birds examined in this study. We also found no correlations between mean muscle DNA content and other muscle structural measurements, such as the number of nuclei per millimeter of fiber, myonuclear domain, and fiber cross-sectional area. Thus, while avian muscle seems more phenotypically plastic than mammalian muscle, the biological processes surrounding myonuclear function may be more closely related to those seen in mammals.

Frequent ploidy changes in Salicaceae indicates widespread sharing of the salicoid whole genome duplication by the relatives of Populus L. and Salix L.

BackgroundsPopulus and Salix belong to Salicaceae and are used as models to investigate woody plant physiology. The variation of karyotype and nuclear DNA content can partly reflect the evolutionary history of the whole genome, and can provide critical information for understanding, predicting, and potentially ameliorating the woody plant traits. Therefore, it is essential to study the chromosome number (CN) and genome size in detail to provide information for revealing the evolutionary process of Salicaceae.ResultsIn this study, we report the somatic CNs of seventeen species from eight genera in Salicaceae. Of these, CNs for twelve species and for five genera are reported for the first time. Among the three subfamilies of Salicaceae, the available data indicate CN in Samydoideae is n = 21, 22, 42. The only two genera, Dianyuea and Scyphostegia, in Scyphostegioideae respectively have n = 9 and 18. In Salicoideae, Populus, Salix and five genera closely related to them (Bennettiodendron, Idesia, Carrierea, Poliothyrsis, Itoa) are based on relatively high CNs from n = 19, 20, 21, 22 to n = 95 in Salix. However, the other genera of Salicoideae are mainly based on relatively low CNs of n = 9, 10, 11. The genome sizes of 35 taxa belonging to 14 genera of Salicaceae were estimated. Of these, the genome sizes of 12 genera and all taxa except Populus euphratica are first reported. Except for Dianyuea, Idesia and Bennettiodendron, all examined species have relatively small genome sizes of less than 1 pg, although polyploidization exists.ConclusionsThe variation of CN and genome size across Salicaceae indicates frequent ploidy changes and a widespread sharing of the salicoid whole genome duplication (WGD) by the relatives of Populus and Salix. The shrinkage of genome size after WGD indicates massive loss of genomic components. The phylogenetic asymmetry in clade of Populus, Salix, and their close relatives suggests that there is a lag-time for the subsequent radiations after the salicoid WGD event. Our results provide useful data for studying the evolutionary events of Salicaceae.

Nuclear DNA content variation within four species of Asian catfish of family Pangasidae and their two interspecific hybrids by flow cytometry

Nuclear DNA content (NDC) of species or population is believed to have been formed naturally by many mechanisms such chromosomal mutation, insertion and deletion, transposable element, and duplication. Additionally, hybridizations and species’ phylogenetic relationship may also contribute to the NDC diversity. This study was aimed to investigate the profile of NDC in four species Asian catfishes of the genera Pangasius including Pangasionodon hypophthalmus, Pangasius djambal, Pangasius nasusutus, Pangasius nieuwenhuisii, interspecific hybrid of female P. hypophthalmus and male P. djambal (Hybrid HD), and female P. hypophthalmus and male P. nasutus (Hybrid HN). Red blood cells (RBC) were taken from the respective species/groups and NDC measurement was performed in an Attune acoustic flowcytometer (ABI) using DAPI staining and chicken, Gallus domesticus, RBC was used as size reference. The results showed that the mean NDC of P. hypophthalmus, P. djambal. P. nasusutus, P. nieuwenhuisii, were 0.960±0.0254 pg, 1.017±0.0510 pg, 1.000±0.0410 pg, 1.074±0.0231 pg, which are within the range of NDC in the other catfish families The NDC values of Hybrid HD and Hybrid HN were1.005±0.0358 and 0.956± 0.0089, respectively. Among the pure line species, the NDC of P. hypophthalmus was the lowest and was different (P<0.05) from those of P. djambal and P. nieuwenhuisii but was not different (P>0.05) from that of the P. nasutus. The NDC of both Hybrid HD and Hybrid HN were not different form their respective parental lines. However, the NDC profiles of both hybrids were different in that the NDC of the former was in between while the latter was below their respective parental lines. Phylogenetically, the NDC diversity within Pangasiid catfish in this study was independent of their phylogenetic relationship based on cytoplasmic and nuclear markers.
 Keywords: Flow cytometry, nuclear DNA content, P.hypophthalmus, P. djambal, P. nasutus, P. nieuwenhuisii, interspecific hybrid.

Substantial intraspecific genome size variation in golden-brown algae and its phenotypic consequences.

While nuclear DNA content variation and its phenotypic consequences have been well described for animals, vascular plants and macroalgae, much less about this topic is known regarding unicellular algae and protists in general. The dearth of data is especially pronounced when it comes to intraspecific genome size variation. This study attempts to investigate the extent of intraspecific variability in genome size and its adaptive consequences in a microalgal species. Propidium iodide flow cytometry was used to estimate the absolute genome size of 131 strains (isolates) of the golden-brown alga Synura petersenii (Chrysophyceae, Stramenopiles), identified by identical internal transcribed spacer (ITS) rDNA barcodes. Cell size, growth rate and genomic GC content were further assessed on a sub-set of strains. Geographic location of 67 sampling sites across the Northern hemisphere was used to extract climatic database data and to evaluate the ecogeographical distribution of genome size diversity. Genome size ranged continuously from 0.97 to 2.02 pg of DNA across the investigated strains. The genome size was positively associated with cell size and negatively associated with growth rate. Bioclim variables were not correlated with genome size variation. No clear trends in the geographical distribution of strains of a particular genome size were detected, and strains of different genome size occasionally coexisted at the same locality. Genomic GC content was significantly associated only with genome size via a quadratic relationship. Genome size variability in S. petersenii was probably triggered by an evolutionary mechanism operating via gradual changes in genome size accompanied by changes in genomic GC content, such as, for example, proliferation of transposable elements. The variation was reflected in cell size and relative growth rate, possibly with adaptive consequences.

Karyotype and nuclear DNA content variation in Passiflora L

The Passiflora genus, which is recognized for its economic and ecological potential, has been studied in botanical, systematic and evolutionary aspects. Currently, Passiflora is represented by five subgenera subdivided into 16 supersections, 31 sections and 13 series. However, their delimitations and relationships are still conflicting. We applied classical cytogenetics to revise the chromosome number of 19 species and to define it for further nine. The classification of chromosome pairs was re-evaluated for nine species and established for further 19. For 24 species, the karyogram was assembled for the first time, and for the other four it was updated. Using flow cytometry, the nuclear DNA content was revisited for 22 species and expanded for 19. Chromosome number 2n = 12 was found for the subgenus Decaloba, as well as 2n = 18 and 2n = 20 for Passiflora, 2n = 24 for Astrophea and Deidamioides, and the unpublished 2n = 48 for P. contracta (subgenus Deidamioides). Metacentric and submetacentric chromosomes predominated in all karyotypes, except in P. lindeniana and P. arborea (subgenus Astrophea), which some acrocentric pairs occur. The nuclear 2C value ranged from 0.59 pg (P. capsularis) to 5.46 pg (P. quadrangularis), with differences exceeding 925 %. The karyotypes and nuclear genome size of the genus Passiflora supported the current subgeneric division. The evaluated characters also corroborate with the hypothesis of x = 6 as the ancestral chromosome number and the diversification by polyploidy and ascendant dysploidy. Furthermore, the cytogenetic and genome size data were complementary to systematic of the genus.

Repetitive sequences and structural chromosome alterations promote intraspecific variations in Zea mays L. karyotype

LTR-retrotransposons, knobs and structural chromosome alterations contribute to shape the structure and organization of the Zea mays karyotype. Our initial nuclear DNA content data of Z. mays accessions revealed an intraspecific variation (2 C = 2.00 pg to 2 C = 6.10 pg), suggesting differences in their karyotypes. We aimed to compare the karyotypes of three Z. mays accessions in search of the differences and similarities among them. Karyotype divergences were demonstrated among the accessions, despite their common chromosome number (2n = 20) and ancestral origin. Cytogenomic analyses showed that repetitive sequences and structural chromosome alterations play a significant role in promoting intraspecific nuclear DNA content variation. In addition, heterozygous terminal deletion in chromosome 3 was pointed out as a cause of lower nuclear 2 C value. Besides this, translocation was also observed in the short arm of chromosome 1. Differently, higher 2 C value was associated with the more abundant distribution of LTR-retrotransposons from the family Grande in the karyotype. Moreover, heteromorphism involving the number and position of the 180-bp knob sequence was found among the accessions. Taken together, we provide insights on the pivotal role played by repetitive sequences and structural chromosome alterations in shaping the karyotype of Z. mays.

Genetic relationship and nuclear dna content variation in Tef [Eragrostis tef (Zucc.) Trotter] accessions.

This study was initiated to reveal genetic relationship of 25 tef (Eragrostis tef (Zucc.) accessions by using 10 SSR markers and to determine DNA content variation by using flow cytometer analysis. Ten markers produced a total of 18 alleles and 11 of those were polymorphic. The mean polymorphism rate was 66.6%. The highest polymorphism information content value was obtained from marker CNLTs370 with 0.69 while markers CNTLs11 and CNTLs133 produced monomorphic bands only. UPGMA analysis divided 25 tef genotypes into three main clades. The accessions PI193511 and PI195934 were distinctly separated from the others. No ploidy differences were determined among the 25 tef accessions. 2C mean nuclear DNA content ranged from 1.406pg to 1.510 with mean of 1.460pg. The results of this study indicated that SSR markers successfully determined genetic relationship of 25 tef accession although they had a low rate of polymorphism. This study also revealed that available tef related SSR markers should be optimized before use and their efficiency may vary based on tef genotypes or accessions used.

Genome Status of Lippia alba Polyploid Complex Long-term in vitro Cultivated

This study is the first report of a genetic stability analysis of a polyploid complex maintained in vitro for a long-time. Twenty-two accessions of Lippia alba, a medicinal species of economic importance, had been maintained under in vitro culture conditions for 7 years through sprouting of axillary buds. Four clones of each accession were analyzed, being three plants from in vitro bank and one cultivated in the field. We investigated the genetic stability of diploid, aneuploid, triploid, tetraploid, and hexaploid accessions. The investigation was carried out using flow cytometry, inter simple sequence repeat (ISSR) and simple sequence repeat (SSR) markers. No significant variation in nuclear DNA content was observed between the in vitro conserved plants and their respective field plant. Out of 23 ISSR primers screened, 8 primers were found to produce clear reproducible bands resulting in a total of 5456 bands. 86.36% of the analyzed plantlets (19 accessions) showed at least one polymorphic band. The polymorphic rate ranged from 1.61 to 33.87%. The SSR markers were used to confirm the absence or low occurrence of variation in accessions that showed no polymorphism or polymorphism for only one ISSR primer. The genetic instability detected in our study at the molecular level may be attributed to the natural instability of L. alba genome combined with the long-time in vitro maintenance.

Small, but surprisingly repetitive genomes: transposon expansion and not polyploidy has driven a doubling in genome size in a metazoan species complex

BackgroundThe causes and consequences of genome size variation across Eukaryotes, which spans five orders of magnitude, have been hotly debated since before the advent of genome sequencing. Previous studies have mostly examined variation among larger taxonomic units (e.g., orders, or genera), while comparisons among closely related species are rare. Rotifers of the Brachionus plicatilis species complex exhibit a seven-fold variation in genome size and thus represent a unique opportunity to study such changes on a relatively short evolutionary timescale. Here, we sequenced and analysed the genomes of four species of this complex with nuclear DNA contents spanning 110–422 Mbp. To establish the likely mechanisms of genome size change, we analysed both sequencing read libraries and assemblies for signatures of polyploidy and repetitive element content. We also compared these genomes to that of B. calyciflorus, the closest relative with a sequenced genome (293 Mbp nuclear DNA content).ResultsDespite the very large differences in genome size, we saw no evidence of ploidy level changes across the B. plicatilis complex. However, repetitive element content explained a large portion of genome size variation (at least 54%). The species with the largest genome, B. asplanchnoidis, has a strikingly high 44% repetitive element content, while the smaller B. plicatilis genomes contain between 14 and 25% repetitive elements. According to our analyses, the B. calyciflorus genome contains 39% repetitive elements, which is substantially higher than previously reported (21%), and suggests that high repetitive element load could be widespread in monogonont rotifers.ConclusionsEven though the genome sizes of these species are at the low end of the metazoan spectrum, their genomes contain substantial amounts of repetitive elements. Polyploidy does not appear to play a role in genome size variations in these species, and these variations can be mostly explained by changes in repetitive element content. This contradicts the naïve expectation that small genomes are streamlined, or less complex, and that large variations in nuclear DNA content between closely related species are due to polyploidy.

First report of genome size and ploidy of the underutilized leguminous tuber crop Yam Bean (Pachyrhizus erosus and P. tuberosus) by flow cytometry

AbstractCytological understanding is an important parameter to understand the genetic architecture of yam bean. The ploidy level and genome size of two cultivated species of yam bean (Pachyrhizus erosus and P. tuberosus) were estimated using flow cytometric analysis of young leaf tissue, with propidium iodide as a fluorescent dye. Six genotypes of P. erosus and three genotypes of P. tuberosus were analysed. Rice (Oryza sativa cv. Nipponbare) and Mung bean (Vigna radiata cv Berken) were used as internal reference standards. Variation of 2C nuclear DNA content among the six P. erousus lines was 4.18%, ranging from 1.17 to 1.22 pg, whereas only 1.8% variation was observed among the three P. tuberosus lines, which ranged from 1.07 to 1.09 pg. Moreover, it was found that the nuclear DNA content of P. tuberosus was lower than that of P. erosus. The result of the flow cytometric analysis showed that all the species were diploid (2n = 2x) and coefficient of variation (CV%) of all the accessions of the two species was less than 3.5%. This is the first report of ploidy analysis and genome size estimation of the leguminous underutilized tuber crop yam bean using flow cytometry. This result will be helpful for yam bean genome sequencing and crop improvement programmes.

Nuclear DNA content variation of herbaceous angiosperm species on 10 global latitudinal transects1,2

Many studies have examined variation in nuclear DNA content across environmental gradients. However, these studies have often produced conflicting results. We speculated that the conflicting phenomenon resulted from insufficient sampling of the taxa and limitations in the geographical range. To clarify whether the relationships between nuclear DNA content and environmental gradients are universally nonlinear across a wide geographical range, we chose 3,290 herbaceous angiosperm species, which have both nuclear DNA values in the Angiosperm DNA C-values database and geographical distribution information in the Global Biodiversity Information Facility (GBIF) database. Then we selected 10 global longitudinal transects each with a span of 15°, and evenly divided each transect (from 82.5°N to 82.5°S) into 22 blocks. We obtained geographical records (presence or absence) of these 3,290 species together with 14 bioclimatic factors within these blocks, and calculated the average DNA 1C-values and genome sizes of the species in each block. By using polynomial functions, we analyzed the correlation of nuclear DNA values with latitude. By using the Gaussian model, we further analyzed the correlation of nuclear DNA values with the 14 bioclimatic factors. Finally, we also performed quantile regression analyses to elucidate the differences in geographical distribution pattern among groups with nuclear DNA values of different sizes. We found that species in equatorial areas had the smallest mean nuclear DNA values, the values increased with latitude for both the northern and southern hemispheres following nonlinear functions. We found that nuclear DNA contents decreased with increasing latitude in the Arctic. The change of nuclear DNA content with latitude was weaker in the species groups with smaller nuclear DNA content than those with a larger nuclear DNA content. Nonlinear relationships (following Gaussian models) also existed between nuclear DNA values and the 14 bioclimatic factors, such as annual precipitation and mean temperature. Therefore, the relationships of nuclear DNA content with either latitude or the 14 bioclimatic factors covarying with latitude are universally nonlinear across a global geographical gradient. Nuclear DNA contents are of ecological significance for angiosperms. There exist obvious differences in the geographical distribution patterns among species groups with nuclear DNA values of different sizes, with a selective advantage for species with small nuclear DNA content in extreme environments.

Estimation of nuclear DNA content and its variation among Indian Tea accessions by flow cytometry.

Nuclear DNA content and genome size variation among 36 Indian tea accessions were analyzed by flow cytometry. Initial standardization of protocols for isolation of nuclei, DNA staining and selection of an internal standard for tea accessions which have significantly high amount of phenolic secondary metabolites in their cytosol was carried out. Results obtained revealed that 2C DNA content of Indian tea is 7.46pg which correspondsto 1C genome size of 3673Mb. Inter accession variation in 2C DNA content was also observed among 35 diploid taxa ranging from 7.23 to 7.73pg which was significant at 1% probability level. The 2C DNA content of triploid (UPASI 3) was observed to be 11.47pg which is concurrent with the expected value. Results obtained showed that Assam and Cambod type tea accession have higher 2C DNA content of 7.73pg whereas Assam Cambod hybrids and Assam China hybrids have reduction in DNA content with 2C amounts, 7.23 and 7.32pg DNA respectively. The present study suggests that the species involved in origin of Indian tea must have differed in their genome sizes owing to significant inter accession variation in nuclear DNA content.

Variation in nuclear DNA content and chromosome numbers in blueberry

Abstract Commercial blueberry production in the U.S. relies on cultivars derived from combinations of different blueberry species. Interspecific hybridization continues to be a vital strategy for blueberry breeding, especially in regards to improving abiotic and biotic stress tolerance to expand the range of production. Blueberry species have many different genome sizes, presumably due to differing ploidy levels and/or DNA content. In some species, such as Vaccinium corymbosum L. and V. pallidum Aiton, there are also different ploidy series available for breeding, further complicating the observed DNA content in elite selections. In this study we determined DNA content in 77 blueberry taxa including 11 species and 64 hybrid cultivars. Among these taxa are 11 diploid, 49 tetraploid, one pentaploid, and 16 hexaploid plants representing southern highbush, northern highbush, low bush, rabitteye, and half high blueberries. DNA content was measured for three separate tissue samples from at least three individual plants per taxa for accuracy. Absolute genome sizes varied significantly (P = 0.05) among ploidy levels, with 2C-value means of 1.09 pg for diploid, 2.10 pg for tetraploid, and 3.60 pg for hexaploid taxa. Holoploid genome size (2C DNA) was significantly correlated with ploidy or presumed chromosome number (2n) (r = 0.96, P = 0.0001) but only weakly correlated with monoploid genome size (1Cx-DNA) (r = 0.43, P = 0.0001).

Nuclear DNA contents of Echinchloa crus-galli and its Gaussian relationships with environments

Previous studies on plant nuclear DNA content variation and its relationships with environmental gradients produced conflicting results. We speculated that the relationships between nuclear DNA content of a widely-distributed species and its environmental gradients might be non-linear if it was sampled in a large geographical gradient. Echinochloa crus-galli (L.) P. Beauv. is a worldwide species, but without documents on its intraspecific variation of nuclear DNA content. Our objectives are: 1) to detect intraspecific variation scope of E. crus-galli in its nuclear DNA content, and 2) to testify whether nuclear DNA content of the species changes with environmental gradients following Gaussian models if its populations were sampled in a large geographical gradient. We collected seeds of 36 Chinese populations of E. crus-galli across a wide geographical gradient, and sowed them in a homogeneous field to get their offspring to determine their nuclear DNA content. We analyzed the relationships of nuclear DNA content of these populations with latitude, longitude, and nineteen bioclimatic variables by using Gaussian and linear models. (1) Nuclear DNA content varied from 2.113 to 2.410 pg among 36 Chinese populations of E. crus-galli, with a mean value of 2.256 pg. (2) Gaussian correlations of nuclear DNA content (y) with geographical gradients were detected, with latitude (x) following y=2.2923*e−(x−24.9360)22*63.79452 (r = 0.546, P < 0.001), and with longitude (x) following y=2.2933*e−(x−116.1801)22*44.74502 (r = 0.672, P < 0.001). (3) Among the nineteen bioclimatic variables, except temperature isothermality, precipitations of the wettest month, the wettest quarter and the warmest quarter, the others could be better fit with nuclear DNA content by using Gaussian models than by linear models. There exists intra-specific variation among 36 Chinese populations of E. crus-galli, Gaussian models could be applied to fit the correlations of its Nuclear DNA content with geographical and most bioclimatic gradients.