Annals of Botany 2008 101(6):NP; doi:10.1093/aob/mcn061
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ContentSnapshots
DNA C-value and the cell cycle
In the largest survey
to date,
Francis et al. (pp. 747–757) show a significant
effect of genome size on 110 cell cycle times regardless of
polyploidy, life cycle or phylogeny. A striking feature of the
findings is an increase in cell cycle time in species with C-values
greater than 25 pg.
Genome size correlation with size at higher phenotypic scales
Knight and Beaulieu (pp. 759–766) examine relationships between genome size, phenotype (cell size,
stomatal density, seed mass, leaf mass per unit area, wood density,
photosynthetic rate, plant height) in 100 angiosperm and gymnosperm
species. Genome size correlations are shown to decrease in predictive
power with increasing phenotypic scale.
The selfish chromosome comes of age (Review)
A century of studies
of B chromosomes is uncovering some of their mysteries
(Jones et al., pp. 767–775). Much is known about their occurrence and distribution, phenotypic
effects and mechanisms of inheritance. Molecular tools are helping
to understand their sequence organization, origin and how transmission
is controlled despite an apparent lack of genes.
Anthocyanin causes pseudo-genome size plasticity
Bennett et al. (pp. 777–790) confirm that cytosolic compounds can bias estimates of genome
size when using flow cytometry. Chopping pea or poinsettia tissue
in buffer with the anthocyanin cyanidin-3-rutinoside reproduces
the effects on propidium iodide-staining shown by natural inhibitors
present in red bracts of poinsettia. This finding has profound
practical and theoretical implications.
Cytochemistry and C-values (Review)
Feulgen absorbance
cytophotometry and flow cytometry are the two most widely employed
methods for nuclear DNA content determination.
Greilhuber (pp. 791–804) presents a selective review and discusses, with examples, the
methodological problems, emphasizes best practice and highlights
a lack of knowledge of the role of secondary plant metabolites
as inhibitors of quantitative DNA staining.
Ups and downs of genome size evolution in Nicotiana
Studies of genome
size evolution following polyploidy usually show either a loss
of DNA or the DNA amount to be the sum of diploid progenitors.
Although reports of genome size increase are rare,
Leitch et al. (pp. 805–814) find genome size increase in five of nine
Nicotiana allopolyploids,
the remaining four showing downsizing.
Evolution of rDNA in Nicotiana Allopolyploids (Review)
Using polyploid species
of
Nicotiana as a model,
Kovarik et al. (pp. 815–823) ask why many eukaryotes have an excess of rRNA genes, why large
numbers of rDNA units become epigenetically silenced, why rDNA
evolution and divergence are often associated with sequence
homogenization and concerted evolution, and if these phenomena
are interrelated?
Allopolyploidization in triticale
Ma and Gustafson (pp. 825–832) suggest that both the cytoplasm and relationships between parental
genomes effect genomic sequence variation during inter-generic
allopolyploidization in triticale. Some sequence changes are
non-random, and appear to be a function of genome relations,
ploidy levels and sequence types. The rye parental genome exhibits
a higher level of changes than the wheat genome.
Colliding genomes – imprinting and the consequences of interploidy crosses
Interploidy crosses
in maize generally result in unviable seed because the endosperm
‘senses’ genomic imbalance.
Pennington et al. (pp. 833–843) reveal reciprocal interploidy crosses in maize have very different
effects on early development, prior to seed abortion –
a likely result of differential epigenetic imprinting of the
male and female gametic genomes.
A genomic microsatellite library in Lolium perenne
Although
Lolium perenne accounts for 70 % of all agricultural use in the UK,
genetic resources are limited.
King et al. (pp. 845–853) describe a microsatellite enriched genomic library of
L. perenne.
This increases the number of genetic markers available for marker
assisted selection in breeding programmes and for gene isolation.
Diversity in wheat D-genome donor species
Using inter-retroelement
amplified polymorphism markers,
Saeidi et al. (pp. 855–861) reveal much genetic diversity in 57 accessions of
Aegilops tauschii from various regions of Iran. The centre of origin appears to
be southeast of the Caspian Sea.
Ph1 locus in hexaploid wheat
Nadia Al-Kaff et al. (pp. 863–872) report the molecular characterization of the major locus (
Ph1)
controlling chromosome pairing in wheat and its hybrids with
wild species. The analysis confirms the linkage of this phenotype
to a cluster of genes that is related to CDK2 in humans and
required for meiosis and prevention of non-homologous pairing.
Meiotic proteome of the temperate cereal rye
Meiosis in cereal
rye is being dissected systematically using translational proteomics
by
Phillips et al. (pp. 873–880). Antibodies against key
structural and recombinogenic proteins of
Arabidopsis thaliana are used to construct spatio-temporal profiles of orthologues
in rye and reveal structural variants on western blots. Meiosis
is surprisingly different in the two species.
Extensive intraspecific chromosome variation in Crassula from New Zealand
A morphological
analysis of
Crassula hunua and
C. ruamahanga by
De Lange et al. (pp. 881–899) fails to find characters to distinguish them despite both species
showing extreme variation in chromosome number and rDNA sequence
variation. A recircumscribed
C. ruamahanga is proposed even
though this new entity is probably a species complex that may
contain hybrid individuals.
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