Variation in chromosomal DNA associated with the evolution of Arachis species.

The 2C nuclear DNA amounts were determined for 99 accessions, representing 23 Arachis species from 8 of 9 taxonomic sections, and two synthetic amphidiploids. Mean 2C DNA amounts varied by 15.20%, ranging from 10.26 to 11.82 pg, between accessions of Arachis hypogaea (2n = 4x = 40). Nuclear DNA content variation (5.33-5.91 pg) was also detected among Arachis duranensis (2n = 2x = 20) accessions. The intraspecific variation in the two species may have resulted from indirect selection for favourable genome sizes in particular environmental conditions. The accessions belonging to A. hypogaea ssp. hypogaea (mean value 11.27 pg) with longer life cycle had significantly larger mean DNA content than the accessions of A. hypogaea ssp. fastigiata (mean value 10.97 pg). For 20 diploid (2n = 2x = 20) species of the genus, 2C nuclear DNA amounts ranged from approximately 3 to 7 pg. The diploid perennial species of section Arachis have about 12% more DNA than the annual species. Comparisons of DNA amounts show that evolutionary rating is not a reliable guide to DNA amounts in generic sections of the genus; lower DNA values with evolutionary advancement were found in sections Heteranthae and Triseminatae, but the same was not true for sections Arachis and Caulorrhizae. Similarly, there is evidence of significant differences in DNA content between 4 ancient sections (Procumbentes, Erectoides, Rhizomatosae, and Extranervosae) of the genus. The occurrence of genome size plasticity in both A. duranensis and A. hypogaea provides evidence that A. duranensis could be one of the diploid progenitors of A. hypogaea. The DNA content in the two synthetic amphidiploids corresponded to the sum value estimated for parental species. Key words : Arachis species, genome size, Arachis hypogaea, Arachis duranensis, intraspecific variation.     

Genome size variation in Arachis hypogaea and A. monticola re-evaluated.

Genome size variation within species is a frequently reported, but still a controversial problem. In the present study, we re-evaluated recently published Feulgen densitometric data on genome size and its infraspecific variation in Arachis hypogaea, and also conducted measurements in one accession of its wild relative A. monticola. The methods applied were propidium iodide flow cytometry and Feulgen densitometry using Pisum sativum as an internal standard. The 2C DNA contents previously published cannot be confirmed, but values obtained in this study are about half as large. Additionally, we could not reproduce the previously reported 1.15-fold variation within A. hypogaea; our data indicate genome size stability between respective accessions of this species. Based on 8.84 pg (2C) for Pisum sativum the DNA amounts (2C) were: 5.914 pg in A. hypogaea, and 5.979 pg in A. monticola.     

Intra- and interspecific variation in genome size in Lathyrus (Leguminosae)

2C nuclear DNA amounts for 24 species of Lathyrus (section Lathyrus ) were determined using flow cytometry. A greater than two-fold variation was observed, ranging from 10.2 pg in L. basalticus to 24.2 pg in L. latifolius. In general, the perennial species had greater DNA amounts than the annuals. Significant intraspecific variation was observed in five species of Lathyrus (from 10.1% in L. annuus to 28% in L. tingitanus). A positive correlation was observed between DNA values obtained by flow cytometry and those previously determined by microdensitometry. Finally, the distribution of DNA amounts in species within section Lathyrus appears to be continuous.     

Genome size variation inCajanus cajan (Fabaceae): A reconsideration

A recent investigation of genome size in certain samples of the pigeonpea,Cajanus cajan, indicates values from 1.55 pg to 1.99 pg (1C level), which is 1.29-fold variation between accessions. In the present analysis those of these accessions which had particularly high or low DNA contents in that study were subjected to a reanalysis using propidium iodide and DAPI flow cytometry and Feulgen densitometry. Only minor differences in genome size, not more than 1.047-fold, were found with flow cytometry, and no significant differences were obtained with Feulgen densitometry. The previously reported genome size cannot be confirmed. It is about half as large and was determined in the present study as 0.825 pg (1C, propidium iodide flow cytometry,Glycine max as standard) and 0.853 pg (1C, Feulgen densitometry,Allium cepa andPisum sativum as standards), respectively.     

利用SSR技术研究花生属种间亲缘关系

用44对SSR特异引物对花生属不同区组的21份种质进行了分析,获得能稳定揭示花生属种间差异的SSR引物34对。34对引物在21份种质中共检测到190个等位基因变异,每个位点上检测的等位变异数为3~11个,平均为5.59个。21份材料间存在很大的遗传变异,平均遗传距离为0.63,变异范围为0.08~0.95。聚类分析表明,区组间的遗传分化大于区组内的遗传分化,匍匐区组的遗传分化大于其他区组的遗传分化,同一物种不同种质间也存在很大的差异。栽培种花生与花生区组材料的亲缘关系相对较近,与花生属的植物学分类一致,其中A基因组的A.duranensis和A.villosa及B基因组的A.bati-zocoi与栽培种花生的亲缘关系更近一些。     

The phylogenetic relationship of possible progenitors of the cultivated peanut

The cultivated peanut (Arachis hypogaea L.) is an allotetraploid composed of A and B genomes. The phylogenetic relationship among the cultivated peanut, wild diploid, and tetraploid species in the section Arachis was studied based on sequence comparison of stearoyl-ACP desaturase and oleoyl-PC desaturase. The topology of the trees for both fatty acid desaturases displayed two clusters; one cluster with A genome diploid species and the other with B genome diploid species. The two homeologous genes obtained for each of the two fatty acid desaturases from the tetraploid species A. hypogaea and A. monticola were separated into the A and B genome clusters, respectively. The gene phylogenetic trees showed that A. hypogaea is more closely related to the diploid species A. duranensis and A. ipaensis than to the wild tetraploid species A. monticola, suggesting that A. monticola is not a progenitor of the cultivated peanut. In addition, for the stearoyl-ACP desaturase, the A. duranensis sequence was identical with one of the sequences of A. hypogaea and the A. ipaensis sequence was identical with the other. These results support the hypothesis that A. duranensis and A. ipaensis are the most likely diploid progenitors of the cultivated tetraploid A. hypogaea.     

A Flow Cytometric Analysis of the Nuclear 2C DNA Content in 17 Phaseolus Species (53 Genotypes)

The genus Phaseolus is characterized by a highly stable karyotype of 2n = 22. Despite this constancy, the size of the chromosomes varies, and crossing of species is possible only in a few cases. We determined the 2C nuclear DNA content of a number of Phaseolus species, cultivars and genotypes by flow cytometry, in order to realize the interspecific and intraspecific variation of the 2C value. The data range from 1.03 pg to 2.18 pg without any clear correlation to systematic relationships. The mean DNA values of wild and cultivated forms, as well as those of Andean and Mesoamerican genotypes, do not differ significantly. The variation is interpreted in terms of some nucleotypic adaptations. The data may be useful for molecular biological analyses, as well as for biotechnological and classical breeding programmes.     

Genome size variation in the genus Carthamus (Asteraceae, Cardueae): systematic implications and additive changes during allopolyploidization

BACKGROUND AND AIMS: Plant genome size is an important biological characteristic, with relationships to systematics, ecology and distribution. Currently, there is no information regarding nuclear DNA content for any Carthamus species. In addition to improving the knowledge base, this research focuses on interspecific variation and its implications for the infrageneric classification of this genus. Genome size variation in the process of allopolyploid formation is also addressed. METHODS: Nuclear DNA samples from 34 populations of 16 species of the genus Carthamus were assessed by flow cytometry using propidium iodide. KEY RESULTS: The 2C values ranged from 2.26 pg for C. leucocaulos to 7.46 pg for C. turkestanicus, and monoploid genome size (1Cx-value) ranged from 1.13 pg in C. leucocaulos to 1.53 pg in C. alexandrinus. Mean genome sizes differed significantly, based on sectional classification. Both allopolyploid species (C. creticus and C. turkestanicus) exhibited nuclear DNA contents in accordance with the sum of the putative parental C-values (in one case with a slight reduction, frequent in polyploids), supporting their hybrid origin. CONCLUSIONS: Genome size represents a useful tool in elucidating systematic relationships between closely related species. A considerable reduction in monoploid genome size, possibly due to the hybrid formation, is also reported within these taxa.     

Genome size and environmental factors in the genus Pinus

Nuclear 1C DNA content in haploid megagametophyte tissue of 18 North American and one exotic Pinus species was determined using scanning microspectrophotometry. The nuclear DNA content in root meristematic cells of Zea mays L. ssp. mays, inbred line Va35 (4C = 10.31 pg) was used as a standard. DNA content measured by microspectrophotometry was verified using laser flow cytometry with two additional standards, Hordeum vulgare cv. Sultan (2C = 11.12 pg) and P. eldarica (2C = 47.30 pg). DNA values obtained by both methods were significantly correlated (r = 0.987). The 1C nuclear DNA content ranged from 21 pg to 31 pg. The ratio of DNA content in embryo tissue of P. eldarica to that in megagametophyte tissue was 1.72 by scanning microspectrophotometry and 1.74 by laser flow cytometry. To date, this is the most comprehensive data set available for North American Pinus species. Relationships between genome size of 18 North American Pinus species and climatic factors and indices of growth were investigated using regression and correlation analyses. Positive correlations were observed between nuclear DNA content and growth indices, minimum seed-bearing age, and seed dimensions. Strong negative correlations were observed between nuclear DNA content and two climatic factors, the lowest mean annual and monthly precipitation (excluding January) and the highest mean monthly spring air temperature. These correlations suggest that the large genome size and its variation in Pinus are adapted responses to the habitats of these species.     

Cloning and Characterization of Chromosomal Markers from a Cot-1 Library of Peanut ( Arachis hypogaea L.)

The cultivated peanut, Arachis hypogaea (AABB, 2n = 40), is an allotetraploid which was probably originated from a hybridization event between 2 ancestors, A. duranensis (A genome) and A. ipaensis (B genome) followed by chromosome doubling. The wild species in the Arachis section are useful genetic resources for genes that confer biotic and abiotic stress resistance for peanut breeding. However, the resource is not well exploited because little information on the genetic, cytogenetic, and phylogenetic relationships between cultivated peanut and its wild relatives is known. Characterization of its chromosome components will benefit the understanding of these issues. But the paucity of information on the DNA sequence and the presence of morphologically similar chromosomes impede the construction of a detailed karyotype for peanut chromosome identification. In our study, a peanut Cot-1 library was constructed to isolate highly and moderately repetitive sequences from the cultivated peanut, and the chromosomal distributions of these repeats were investigated. Both genome and chromosome specific markers were identified that allowed the distinguishing of A and B genomes in tetraploid peanut and a possible karyotyping of peanut chromosomes by FISH. In particular, a 115-bp tandem repetitive sequence was identified to be a possible centromere repetitive DNA, mainly localized in the centromeres of B chromosomes, and a partial retrotransposable element was also identified in the centromeres of B chromosomes. The cloning and characterization of various chromosomal markers is a major step for FISH-based karyotyping of peanut. The FISH markers are expected to provide a reference tool for sequence assembly, phylogenetic studies of peanut and its wild species, and breeding.     

Genome size in 21 Artemisia L. species (Asteraceae, Anthemideae): systematic, evolutionary, and ecological implications.

Genome size was estimated by flow cytometry in 24 populations belonging to 22 Artemisia taxa (21 species, 1 with two subspecies), which represent the distinct subgenera, life forms, basic chromosome numbers, and ploidy levels in the genus. 2C nuclear DNA content values range from 3.5 to 25.65 pg, which represents a more than sevenfold variation. DNA content per haploid genome ranges from 1.75 to 5.76 pg. DNA amount is very well correlated with karyotype length and ploidy level. Some variations in genome size have systematic and evolutionary implications, whereas others are linked to ecological selection pressures.     

Limited Genome Size Variation in Sesleria albicans

The extent and significance of intraspecific genome size variationin plants continues to be a matter of discussion: in some speciesconsiderable variation has been described, while no variationhas been detected in other taxa. In the present study, intraspecificgenome size variation was analysed in a perennial grass Sesleriaalbicans Kit. ex Schult. (Poaceae). Flow cytometry was usedfor the analysis of nuclear DNA content in ten geographicallyisolated populations ofS. albicans . Despite long-term isolationand lack of gene-flow between the populations, only negligibleinter-population differences were found. Although the differencesbetween the populations were statistically significant, themaximum inter-population difference reached only 1.6% of themean 2C value (9.78 ± 0.04 pg). The variation was notcorrelated with geographical location or with altitude of thepopulations analysed. The present study clearly demonstratesthat S. albicans belongs to the plant taxa with a highly stablegenome size. Copyright 2000 Annals of Botany Company Sesleria albicans, genome size, nuclear DNA content, intraspecific variation, flow cytometry, Europe     

Intraspecific genome size variation and morphological differentiation of Ranunculus parnassifolius (Ranunculaceae), an Alpine–Pyrenean–Cantabrian polyploid group

The aim of this study was to assess genome size variation and multivariate morphometric analyses to ascertain cytotype distribution patterns and the morphological differentiation within the Ranunculus parnassifolius group in the Pyrenees and the Alps. Although divergences in nuclear DNA content among different species within a genus are widely acknowledged, intraspecific variation is still a somewhat controversial issue. Holoploid and monoploid genome sizes (C‐ and Cx‐values) were determined using propidium iodide flow cytometry in 125 plants of R. parnassifolius s.l. distributed across four European countries. Three different DNA ploidy levels were revealed in the study area: diploid (2n ～ 2x, 57.14%), triploid (2n ～ 3x, 1.19%), and tetraploid (2n ～ 4x, 41.67%). The mean population 2C‐values ranged from 8.15 pg in diploids to 14.80 pg in tetraploids, representing a ratio of 1 : 1.8. Marked intraspecific/interpopulation differences in nuclear DNA content were found. Diploid populations prevail in the Pyrenees, although tetraploid cytotypes were reported throughout the distribution area. In general, mixed‐cytotype populations were not found. The Spearman correlation coefficient did not reveal significant correlations between genome size and altitude, longitude, or latitude. Morphometric analyses and cluster analyses based on genome size variation revealed the presence of three major groups, which exhibited a particular biogeographical pattern. A new cytotype, DNA triploid, was found for the first time. Tetraploid populations showed constant nuclear DNA levels, whereas diploid populations from the Pyrenees, in which introgressive hybridization is suggested as a presumable trigger for genome size variation, did not. Scenarios for the evolution of geographical parthenogenesis in R. parnassifolius s.l. are discussed. Finally, the different levels of effectiveness between plant and animal reference standards are analysed. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 251–271.     

Karyotypes, chromosome bands and genome size variation in New Zealand endemic gymnosperms

Karyotype studies on 20 taxa of gymnosperms endemic to New Zealand show a wide diversity of chromosome number and form. Fluorochrome banding with DAPI and CMA reveals a depauperate pattern of bands with CMA and no reliable banding with DAPI. Characteristically one pair of chromosomes shows a prominent CMA band, which may or may not be associated with a secondary constriction. A band size polymorphism was observed in all plants ofDacrycarpus dacrydioides, irrespective of the sex of the plant. Measurements of genome size by flow cytometry show a range of values from 12.3 pg to 40.0 pg DNA per 2C nucleus. Intraspecific variation in genome size was observed inManoao colensoi.     

2C DNA variation and relationships among New World species of the genus Lupinus (Fabaceae)

The 2C DNA values in 38 species and accessions of the genus Lupinus (Fabaceae) from the New World have been analysed using flow cytometry. They are representatives of North and South American species (the Atlantic and the Andean regions). Estimated 2C DNA values ranged from 1.08 pg in L. pusillus to 2.68 pg in L. albicaulis (both from North America), that is a variation of more than 2.5-fold. The variation for North American lupins was much higher than that for South American ones. Statistical analysis of the data resulted in a grouping that showed for North American lupins some correlation with the length of life cycle. Discussion concerns some aspects of the evolution of the genus.     

野生花生种质的SSR遗传多样性

以花生属(Arachis)6个区组24种(包括栽培种)84份种质为材料,用SSR技术对其亲缘关系和遗传多样性进行了分析.从206对SSR引物中筛选到59对能扩增出稳定的多态性条带的引物,这些引物能在花生属基因组DNA中扩增出1～6个DNA片段.结果表明,84份种质的遗传距离为0.04～0.93,平均为0.64,其中匍匐区组的A.appressipila的2份种质(G4与G5)的遗传距离最小(0.04),匍匐区组的A.rigonii(G14)与根茎区组的A.glabrata(G28)的遗传距离最大(0.93).聚类分析结果与花生属的区组分类基本一致,栽培种花生被聚在花生区组中,而且7份栽培种被聚在同一亚亚组中,相同植物学类犁(相当于变种)的材料均被分别聚在一起.异形花区组与直立区组的亲缘关系最近,与花生区组的亲缘关系较近的是匍匐区组.花牛区组的二倍体野生种A.villosa、A.duranensis和A.benensis与栽培种化生关系较近,可以作为桥梁物种来转移其他野生花生的优良基因.     

Chromosome numbers and DNA?C values in the genus Lippia (Verbenaceae)

The genus Lippia comprises herbs, shrubs, and small trees, including many species with medicinal properties. The species are distributed throughout South and Central America and Tropical Africa, but the majority of them occur in Brazil, Paraguay, and Argentina. The DNA?C value of 28 Brazilian species has been estimated by flow cytometry. Estimated DNA?C values ranged from 0.825?pg (L. corymbosa) to 2.150?pg (L.?brasiliensis). In addition, new chromosome numbers of 12 species have also been described, and meiotic cells with 12, 13, and 14 chromosome pairs were observed. A straightforward correlation between chromosome number and DNA?C value was not observed, probably due to two outlier species of Lippia that have been transferred from the genus Lantana. In general, the data confirm previous reports regarding the variation within the taxonomic sections and also suggest a new revision in section Zapania. Aspects of karyotypic evolution of the genus are also discussed.     

On the evolution of genome size of birds

We measured genome size (nuclear DNA content) by fluorescence flow cytometry in 55 species of birds representing 12 different orders. Similar studies were performed in approximately 100 species by laboratories using absorption cytophotometry of Feulgen-stained nuclei. Although there have been apparent discrepancies in the assigned values for the species used as a reference, the values obtained in the different laboratories are generally in agreement. When the data are standardized in relation to a diploid (2C) value of 2.5 picograms (pg) of DNA for the domestic chicken (Gallus gallus domesticus), the mean for DNA content in 135 species representing 17 orders is 2.82 +/- 0.33 (SD) pg with a range of 2.0-3.8 pg. Thus the genome size of birds is the most conservative of any vertebrate class and, all values considered, is smaller and more uniform in size than previous estimates would indicate. This could be explained by a previously unexplored hypothesis: that the genome of birds has evolved from a small ancestral genome that was reduced before emergence of the protoavian.