Rice bacterial artificial chromosome clones containing centromeric DNA were isolated by using a DNA sequence (pSau3A9) that is present in the centromeres of Gramineae species. Seven distinct repetitive DNA elements were isolated from a 75-kilobase rice bacterial artificial chromosome clone. All seven DNA elements are present in every rice centromere as demonstrated by f luorescence in situ hybridization. Six of the elements are middle repetitive, and their copy numbers range from Ϸ50 to Ϸ300 in the rice genome. Five of these six middle repetitive DNA elements are present in all of the Gramineae species, and the other element is detected only in species within the Bambusoideae subfamily of Gramineae. All six middle repetitive DNA elements are dispersed in the centromeric regions. The seventh element, the RCS2 family, is a tandem repeat of a 168-bp sequence that is represented Ϸ6,000 times in the rice genome and is detected only in Oryza species. Fiber-f luorescence in situ hybridization analysis revealed that the RCS2 family is organized into long uninterrupted arrays and resembles previously reported tandem repeats located in the centromeres of human and Arabidopsis thaliana chromosomes. We characterized a large DNA fragment derived from a plant centromere and demonstrated that rice centromeres consist of complex DNA, including both highly and middle repetitive DNA sequences.Centromeres are one of the most characteristic landmarks of eukaryotic chromosomes. The centromeric region is the site for mitotic and meiotic spindle fiber attachment and is responsible for sister chromatid association. Thus centromeres play a central role in the process of chromosomal segregation and transmission in cell divisions. The molecular organization of centromeres has been studied extensively in yeast, Drosophila melanogaster, and humans. Whereas the centromeres of budding yeast (Saccharomyces cerevisiae) chromosomes are structurally simple, specified by only a 125-bp, single-copy DNA sequence (1-2), the centromeres from higher eukaryotic species, such as D. melanogaster and humans, encompass several hundred kilobases (kb) or even megabases of DNA and contain repetitive DNA sequences (3-7).Thus far, only limited information is available for the organization of plant centromeres. Peacock et al. (8) first isolated a repetitive DNA element from the maize knobs that can act as neocentromeres in certain genetic backgrounds. A repetitive DNA element also was cloned from the centromeres of the supernumerary B chromosomes of maize (9-10). Part of this B-specific DNA element shows strong homology to the maize knob sequences. A 180-bp tandem repeat (pAL1 family) is the major component of the centromeric regions of Arabidopsis thaliana chromosomes. The genomic organization of this repeat family shares similarities to the alpha satellite DNA at the human centromeres (11)(12)(13)(14). Recently, two repetitive DNA elements, pSau3A9 and CCS1, were isolated from sorghum (Sorghum bicolor) (15) and Brachypodium sylvaticum (16), respectivel...

Aim Biodiversity studies typically use species, or more recently phylogenetic diversity (PD), as their analysis unit and produce a single map of observed diversity. However, observed biodiversity is not necessarily an indicator of significant biodiversity and therefore should not be used alone. By applying a small number of additional metrics to PD, with associated statistical tests, we can determine whether more or less of the phylogeny occurs in an area, whether branch lengths in an area are longer or shorter, and whether more long or short-branched endemism occurs in an area, than expected under a null model. Location Australian continent.Methods We used a phylogeny sampling 90% of Australia's angiosperm genera, and 3.4 million georeferenced plant specimens downloaded from Australia's Virtual Herbarium (AVH), to calculate PD, relative phylogenetic diversity (RPD) and relative phylogenetic endemism (RPE). Categorical analysis of neo-and palaeo-endemism (CANAPE) and randomization tests were performed to determine statistical significance.Results We identify several combinations of significant PD and endemism across the continent that are not seen using observed diversity patterns alone. Joint interpretation of these combinations complements the previous interpretations of Australia's plant evolutionary history. Of conservation concern, only 42% of the significant endemism cells found here overlap with existing nature reserves.Main conclusions These spatial phylogenetic methods are feasible to apply to a whole flora at the continental scale. Observed richness or PD is inadequate to fully understand the patterns of biodiversity. The combination of statistical tests applied here can be used to better explain biodiversity patterns and the evolutionary and ecological processes that have created them. The spatial phylogenetic methods used in this paper can be also be used to identify conservation priorities at any geographical scale or taxonomic level.

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Sexual reproduction is both extremely costly and widespread relative to asexual reproduction, meaning that it must also confer profound advantages in order to persist. One theorized benefit of sex is that it facilitates the clearance of harmful mutations, which would accumulate more rapidly in the absence of recombination. The extent to which ineffective purifying selection and mutation accumulation are direct consequences of asexuality and whether the accelerated buildup of harmful mutations in asexuals can occur rapidly enough to maintain sex within natural populations, however, remain as open questions. We addressed key components of these questions by estimating the rate of mutation accumulation in the mitochondrial genomes of multiple sexual and asexual representatives of Potamopyrgus antipodarum, a New Zealand snail characterized by mixed sexual/asexual populations. We found that increased mutation accumulation is associated with asexuality and occurs rapidly enough to be detected in recently derived asexual lineages of P. antipodarum. Our results demonstrate that increased mutation accumulation in asexuals can differentially affect coexisting and ecologically similar sexual and asexual lineages. The accelerated rate of mutation accumulation observed in asexual P. antipodarum provides some of the most direct evidence to date for a link between asexuality and mutation accumulation and implies that mutational buildup could be rapid enough to contribute to the short-term evolutionary mechanisms that favor sexual reproduction.

The eucalypts, which include Eucalyptus, Angophora and Corymbia, are native to Australia and Malesia and include over 800 named species in a mixture of diverse and depauperate lineages. We assessed the fit of the eucalypt taxonomic classification to a phylogeny of 711 species scored for DNA sequences of plastid matK and psbA–trnH, as well as nuclear internal transcribed spacer and external transcribed spacer. Two broadly similar topologies emerge from both maximum likelihood and Bayesian analyses, showing Angophora nested within Corymbia, or Angophora sister to Corymbia. The position of certain species-poor groups on long branches fluctuated relative to the three major Eucalyptus subgenera, and positions of several closely related species within those subgenera were unstable and lacked statistical support. Most sections and series of Eucalyptus were not recovered as monophyletic. We calibrated these phylogenies against time, using penalised likelihood and constraints obtained from fossil ages. On the basis of these trees, most major eucalypt subgenera arose in the Late Eocene and Early Oligocene. All Eucalyptus clades with taxa occurring in south-eastern Australia have crown ages <20million years. Several eucalypt clades display a strong present-day geographic disjunction, although these clades did not have strong phylogenetic statistical support. In particular, the estimated age of the separation between the eudesmids (Eucalyptus subgenus Eudesmia) and monocalypts (Eucalyptus subgenus Eucalyptus) was consistent with extensive inland water bodies in the Eocene. Bayesian analysis of macroevolutionary mixture rates of net species diversification accelerated in five sections of Eucalyptus subgenus Symphyomyrtus, all beginning 2–3million years ago and associated with semi-arid habitats dominated by mallee and mallet growth forms, and with open woodlands and forests in eastern Australia. This is the first time that a calibrated molecular study has shown support for the rapid diversification of eucalypts in the recent past, most likely driven by changing climate and diverse soil geochemical conditions.

Sequences of nuclear ribosomal DNA internal (ITS) and external (ETS) transcribed spacers were used to generate a phylogeny of Acacia Mill. s.str. (synonyms: Acacia subg. Phyllodineae (DC.) Seringe; Racosperma Mart.). This study included 109 exemplar taxa from all seven sections recognised in previous classifications, and represents the largest sampling of diversity for molecular phylogenetics of Acacia s.str. undertaken so far. Four main clades were identified from the combined dataset of ITS and ETS using parsimony and Bayesian analyses. Two of these clades consist mostly of uninerved phyllodinous taxa assigned to sect. Phyllodineae. One clade includes taxa related to A. victoriae and A. pyrifolia, and the second comprises taxa in the A. murrayana species group. These taxa occur predominantly in semi‐arid and arid regions. Relationships also resolve the previously identified Pulchelloidea clade, which includes members of sects. Pulchellae, Alatae, Phyllodineae and Lycopodiifoliae. A large clade with limited phylogenetic resolution was also identified (the "p.u.b. clade"). This is an assemblage of plurinerved and uninerved phyllodinous taxa and also bi‐pinnate taxa from sect. Botrycephalae. Clades are discussed with reference to morphological characters, and while some morphological states are correlated with clades, including seedling ontogeny, inflorescence and phyllode nerves, clear synapomorphies remain to be identified. Traditional classifications of Acacia s.str. are artificial and a preliminary informal classification based on phylogenetic relationships within Acacia s.str. is proposed.

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Morphological and genetic differences separating the subgenera of Acacia s.l. and molecular evidence that the genus Acacia s.l. is polyphyletic necessitate transfer of the following New World taxa from Acacia subgenus Aculeiferum Vassal to Senegalia, resulting in fifty-one Phytologia (June 2006) 88(1) Pedley (1986), all of which should be transferred to the genus Acaciella.