Short day-mediated cessation of growth requires the downregulation of AINTEGUMENTALIKE1 transcription factor in hybrid aspen

Day length is a key environmental cue regulating the timing of major developmental transitions in plants. For example, in perennial plants such as the long-lived trees of the boreal forest, exposure to short days (SD) leads to the termination of meristem activity and bud set (referred to as growth cessation). The mechanism underlying SD-mediated induction of growth cessation is poorly understood. Here we show that the AIL1-AIL4 (AINTEGUMENTALIKE) transcription factors of the AP2 family are the downstream targets of the SD signal in the regulation of growth cessation response in hybrid aspen trees. AIL1 is expressed in the shoot apical meristem and leaf primordia, and exposure to SD signal downregulates AIL1 expression. Downregulation of AIL gene expression by SDs is altered in transgenic hybrid aspen plants that are defective in SD perception and/or response, e.g. PHYA or FT overexpressors. Importantly, SD-mediated regulation of growth cessation response is also affected by overexpression or downregulation of AIL gene expression. AIL1 protein can interact with the promoter of the key cell cycle genes, e.g. CYCD3.2, and downregulation of the expression of D-type cyclins after SD treatment is prevented by AIL1 overexpression. These data reveal that execution of SD-mediated growth cessation response requires the downregulation of AIL gene expression. Thus, while early acting components like PHYA and the CO/FT regulon are conserved in day-length regulation of flowering time and growth cessation between annual and perennial plants, signaling pathways downstream of SD perception diverge, with AIL transcription factors being novel targets of the CO/FT regulon connecting the perception of SD signal to the regulation of meristem activity.

Differential response of the homoploid hybrid species Iris nelsonii (Iridaceae) and its progenitors to abiotic habitat conditions

PREMISE OF THE STUDY

Homoploid hybrid speciation involves the evolution of reproductive isolation between a hybrid lineage and its progenitors without a change in chromosome number. Ecological divergence presumably plays a large role in the stabilization of hybrid lineages, as all homoploid hybrid species described to date are reported to be ecologically divergent from their progenitors. However, the described ecological divergence in most systems is anecdotal and has not been empirically tested.

METHODS

We assessed the vegetative response of Iris nelsonii, a homoploid hybrid species, and its three progenitor species, I. brevicaulis, I. fulva, and I. hexagona, to different abiotic conditions (i.e., varied sunlight availability and flooding conditions) that largely characterize the habitats of these four species in their natural habitats in Louisiana, USA.

KEY RESULTS

The species differed in their responses to the water-level treatment for many of the response variables, including rhizome weight, ramet growth, plant height, and two principal components used to characterize the data. The species differed in their response to the light-level treatment for root allocation and the principal component used to characterize plant size. Iris nelsonii significantly differed from its progenitors, including its most closely related progenitor species, in response to many of the treatments.

CONCLUSIONS

The differential response to abiotic habitat conditions of I. nelsonii suggests that this species is ecologically divergent from its progenitor species.

Agronomic performance of F1, F2 and F3 hybrids between weedy rice and transgenic glufosinate-resistant rice

BACKGROUND

Studies of hybrid fitness, of which agronomic performance may be an indicator, can help in evaluating the potential for introgression of a transgene from a transgenic crop to wild relatives. The objective of this study was to assess the agronomic performance of reciprocal hybrids between two transgenic glufosinate-resistant rice lines, Y0003 and 99-t, and two weedy rice accessions, WR1 and WR2, in the greenhouse.

RESULTS

F1 hybrids displayed heterosis in height, flag leaf area and number of spikelets per panicle. The agronomic performance of F1 between WR1 and Y0003 was not affected by crossing direction. The tiller and panicle numbers of F1 individuals were higher than their F2 counterparts. However, these traits did not change significantly from the F2 to the F3 generation or in hybrids with weedy rice as maternal or paternal plants. For all hybrids, the in vitro germination rates of fresh pollen were similar and significantly lower than those of their parents, seed sets were similar to or of lower value than those of weedy rice parents and seed shattering characteristics were partially suppressed, but the survival of hybrids over winter in the field was similar to that of weedy rice parents. All F1, F2 and F3 hybrids had similar composite agronomic performance to weedy rice parents.

CONCLUSION

There was no significant decrease in the composite agronomic performance of any of the hybrids compared with weedy rice. This implies that gene flow from transgenic cultivated rice to weedy rice could occur under natural conditions.

Growth, leaf traits and litter decomposition of roadside hybrid aspen (Populus tremula L.× P. tremuloides Michx.) clones

Road traffic contributes considerably to ground-level air pollution and is therefore likely to affect roadside ecosystems. Differences in growth and leaf traits among 13 hybrid aspen (Populus tremula × P. tremuloides) clones were studied in relation to distance from a motorway. The trees sampled were growing 15 and 30 m from a motorway and at a background rural site in southern Finland. Litter decomposition was also measured at both the roadside and rural sites. Height and diameter growth rate and specific leaf area were lowest, and epicuticular wax amount highest in trees growing 15m from the motorway. Although no significant distance × clone interactions were detected, clone-based analyses indicated differences in genotypic responses to motorway proximity. Leaf N concentration did not differ with distance from the motorway for any of the clones. Leaf litter decomposition was only temporarily retarded in the roadside environment, suggesting minor effects on nutrient cycling.

3D reconstructions of quail-chick chimeras provide a new fate map of the avian scapula

Limbed vertebrates have functionally integrated postcranial axial and appendicular systems derived from two distinct populations of embryonic mesoderm. The axial skeletal elements arise from the paraxial somites, the appendicular skeleton and sternum arise from the somatic lateral plate mesoderm, and all of the muscles for both systems arise from the somites. Recent studies in amniotes demonstrate that the scapula has a mixed mesodermal origin. Here we determine the relative contribution of somitic and lateral plate mesoderm to the avian scapula from quail-chick chimeras. We generate 3D reconstructions of the grafted tissue in the host revealing a very different distribution of somitic cells in the scapula than previously reported. This novel 3D visualization of the cryptic border between somitic and lateral plate populations reveals the dynamics of musculoskeletal morphogenesis and demonstrates the importance of 3D visualization of chimera data. Reconstructions of chimeras make clear three significant contrasts with existing models of scapular development. First, the majority of the avian scapula is lateral plate derived and the somitic contribution to the scapular blade is significantly smaller than in previous models. Second, the segmentation of the somitic component of the blade is partially lost; and third, there are striking differences in growth rates between different tissues derived from the same somites that contribute to the structures of the cervical thoracic transition, including the scapula. These data call for the reassessment of theories on the development, homology, and evolution of the vertebrate scapula.

Quantifying the effect of nitrogen-induced physiological and structural changes on poplar growth using a carbon-balance model

We evaluate the importance of changes in photosynthetic capacity, respiration rates, root shoot ratio, pipe model parameters and specific leaf area in the early-growth response of hybrid poplar to nitrogen availability. Juvenile growth simulations for trees with three different levels of leaf nitrogen concentration (N(leaf)) (low (1.2%), medium (2.4%) and high (3.6%)) were conducted with the carbon-balance model CROBAS. Five-year growth simulations showed the diameter and height of poplar trees to be, respectively, four and three times larger in plants with 2.4% N(leaf) compared with those with 1.2% N(leaf). Increasing N(leaf) from 2.4 to 3.6% resulted in 34 and 16% higher diameter and height growth of trees. According to the model, changes in the photosynthetic capacity accounted for most of the differences in growth between trees with different levels of N(leaf); the other parameters were much less influential. This suggests that in fast-growing early-successional broadleaved species such as poplars, physiological rather than allocational and morphological traits predominate in determining growth, at least under non-limiting light conditions.

Evaluation of the genotype, environment and their interaction on carotenoid and ascorbic acid accumulation in tomato germplasm

BACKGROUND

Tomatoes are an important source of antioxidants (carotenoids, vitamin C, etc.) owing to their high level of consumption. There is great interest in developing cultivars with increased levels of lycopene, β-carotene or L-ascorbic acid. There is necessary to survey new sources of variation. In this study, the potential of improvement for each character in tomato breeding programmes, in a single or joint approach, and the nature of genotype (G), environment (E) and G × E interaction effects in the expression of these characters were investigated.

RESULTS

The content of lycopene, β-carotene and ascorbic acid determined was very high in some phenotypes (up to 281, 35 and 346 mg kg(-1) respectively). The important differences in the three environments studied (with some stressing conditions in several situations) had a remarkable influence in the phenotypic expression of the functional characters evaluated. Nevertheless, the major contribution came from the genotypic effect along with a considerable G × E interaction.

CONCLUSION

The joint accumulation of lycopene and β-carotene has a high genetic component. It is possible to select elite genotypes with high content of both carotenoids in tomato breeding programmes but multi-environment trials are recommended. The improvement of ascorbic acid content is more difficult because the interference of uncontrolled factors mask the real genetic potential. Among the accessions evaluated, there are four accessions with an amazing genetic potential for functional properties that can be used as donor parents in tomato breeding programmes or for direct consumption in quality markets.

Response and recovery of hybrid sturgeon from subchronic oral administration of cyanobacteria

A 90-day growth trial was conducted on hybrid sturgeon (Acipenser baeri ♀ × A. gueldenstaedtii ♂) to investigate the effect of dietary inclusion of cyanobacteria on growth, feed utilization, and fish tissue microcystins (MCs) accumulation and the recovery of fish when they were free of cyanobacteria. Four diets were formualted isonitrogenous and isocaloric to contain different MCs concentrations: the control diet (free of cyanobacteria), low cyanobacteria diet (LCD, 26.60 μg MCs/g diet), medium cyanobacteria diet (MCD, 78.82 μg MCs/g diet), and high cyanobacteria diet (HCD, 201.03 μg MCs/g diet). During the first 47 days, each diet was fed to fish in five replicates and then all fish were fed the control diet during the next 43 days. The results showed that a dose-dependent decrease in feeding rate (FR) and specific growth rate (SGR) were observed in the fish fed with MCD and HCD. MCs contents in fish liver, intestine, and dorsal white muscle increased with dietary MCs and were time dependent (P < 0.05). After the 43-day recovery, there were no significant differences in FR or SGR between the fish previously fed LCD or MCD and the fish fed with the control diet (P > 0.05), while the fish previously fed HCD showed higher FR and SGR than those fed the control diet (P < 0.05). MCs clearance in fish liver and intestine showed time-dependence during the 43-day recovery.

Impact of interspecific hybridization between crops and weedy relatives on the evolution of flowering time in weedy phenotypes

BACKGROUND

Like conventional crops, some GM cultivars may readily hybridize with their wild or weedy relatives. The progressive introgression of transgenes into wild or weedy populations thus appears inevitable, and we are now faced with the challenge of determining the possible evolutionary effects of these transgenes. The aim of this study was to gain insight into the impact of interspecific hybridization between transgenic plants and weedy relatives on the evolution of the weedy phenotype.

METHODOLOGY/PRINCIPAL FINDINGS

Experimental populations of weedy birdseed rape (Brassica rapa) and transgenic rapeseed (B. napus) were grown under glasshouse conditions. Hybridization opportunities with transgenic plants and phenotypic traits (including phenological, morphological and reproductive traits) were measured for each weedy individual. We show that weedy individuals that flowered later and for longer periods were more likely to receive transgenic pollen from crops and weed × crop hybrids. Because stem diameter is correlated with flowering time, plants with wider stems were also more likely to be pollinated by transgenic plants. We also show that the weedy plants with the highest probability of hybridization had the lowest fecundity.

CONCLUSION/SIGNIFICANCE

Our results suggest that weeds flowering late and for long periods are less fit because they have a higher probability of hybridizing with crops or weed × crop hybrids. This may result in counter-selection against this subset of weed phenotypes, and a shorter earlier flowering period. It is noteworthy that this potential evolution in flowering time does not depend on the presence of the transgene in the crop. Evolution in flowering time may even be counter-balanced by positive selection acting on the transgene if the latter was positively associated with maternal genes promoting late flowering and long flowering periods. Unfortunately, we could not verify this association in the present experiment.

Silicon influence on maize, Zea mays L., hybrids exposed to cadmium treatment

Thirty Zea mays L. hybrids were screened using hydroponically-grown seedlings treated in the medium with high cadmium content (100 microM Cd(NO(3))(2) x 4 H(2)O). Measurements showed conspicuous differences between the hybrids in the growth parameters in Cd treated plants. Hybrids differed greatly in Cd accumulation and translocation. Root/shoot ratio in Cd concentration ranged from 2.78 to 12.83. The majority of the heavy metal was localized in the root system. Five hybrids were chosen and the effect of silicon (5 mM) effect on high-level cadmium toxicity symptoms was investigated. Silicon decreased Cd accumulation in roots and its translocation into the shoots.

Size-dependent growth of individual Atlantic salmon Salmo salar alevins from hatch to first feeding

Variation in egg size, hatch timing and size at hatch, and their influence on individual growth rates of Atlantic salmon Salmo salar alevins up to first feeding were examined in pure strain and hybrid crosses of fish from Scotland and Canada. At the intra-female, intra-cross type and inter-cross type levels, specific growth rates prior to first feed were strongly size dependent, with smaller and later hatching alevins growing significantly faster. The magnitude of this size-dependent growth was greatest in the hybrid crosses. This resulted in a 40% reduction in the coefficient of variation (c.v.) in alevin size from post-hatch to first feeding at the intra-female level, and a reduction of both intra- and inter-cross differences in alevin sizes in the same period.

Existence of vigorous lineages of crop-wild hybrids in Lettuce under field conditions

Plant to plant gene flow is a route of environmental exposure for GM plants specifically since crosses with wild relatives could lead to the formation of more vigorous hybrids, which could increase the rate of introgression and the environmental impact. Here, we test the first step in the process of potential transgene introgression: whether hybrid vigor can be inherited to the next generation, which could lead to fixation of altered, i.e., elevated, quantitative traits. The potential for a permanent elevated fitness was tested using individual autogamous progeny lineages of hybrids between the crop Lactuca sativa (Lettuce) and the wild species Lactuca serriola (Prickly Lettuce). We compared progeny from motherplants grown under either greenhouse or field conditions. The survival of young plants depended strongly on maternal environment. Furthermore, we observed that offspring reproductive fitness components were correlated with maternal fitness. Our study demonstrates that post-zygotic genotypic sorting at the young plants stage reduces the number of genotypes non-randomly, leading to inheritance of high levels of reproductive traits in the surviving hybrid lineages, compared to the pure wild relatives. Consequently, directional selection could lead to displacement of the pure wild relative and fixation of more vigorous genome segments originating from crops, stabilizing plant traits at elevated levels. Such information can be used to indentify segments which are less likely to introgress into wild relative populations as a target for transgene insertion.

[Features of alloplasmic wheat-barley substitution and addition lines (Hordeum marinum subsp. gussoneanum)-triticum aestivum]

Two alloplasmic wheat-barley substitution lines were studied: a line replaced at three pairs of chromosomes 1Hmr((IB), 5Hmar(5D), and 7Hmar(7D), and the disomic-substituted line 7Hma(7D). The lines were constructed on the basis of individual plants from BCIF8- and BC2F6 progeny of barley-wheat hybrids (H. marinum subsp. gussoneanum Hudson (=H. geniculatum All.) (2n = 28) x T. aestivum L.) (2n = 42) (Pyrotrix 28), respectively. Moreover, the alloplasmic wheat-barley ditelosomic addition line 7HLma' isolated among plants from the BC1F6 progeny of a barley-wheat amphiploid was studied, which in this work corresponds to BC2F10 and BC2F11 progeny. It was ascertained that when grown in the field, these alloplasmic lines manifest stable self-fertility. Plants of the given lines are characterized by low height, shortened ears, the fewer number of stems and ears, and of spikelets in the ear, by decreased grain productivity and weight of 1000 grains, in comparison with the common wheat cultivar Pyrotrix 28. The inhibition of trait expression in alloplasmic wheat-barley substitution and addition lines may be connected not only with the influence of wild barley chromosomes functioning in the genotypic environment of common wheat, but also with the effect of the barley cytoplasm. The alloplasmic line with substitution of chromosomes 1Hmar(1B), 5Hmar(5D), and 7Hmar(7D) or the alloplasmic line 7HLmar with ditelosomic addition have, in comparison with the common wheat cultivar Pyrotrix 28, an increased grain protein content, which is explained by the effect of wild barley H. marinum subsp. gussoneanum chromosomes.

Chromosome elimination, addition and introgression in intertribal partial hybrids between Brassica rapa and Isatis indigotica

BACKGROUND AND AIMS

Partial hybrids with female-parent-type phenotypes and chromosome numbers but altered genomic compositions have been reported in wide crosses of several plants. In order to introgress desirable genes from a wild relative, Isatis indigotica (a dye and medicinal plant; 2n = 14), into Brassica crops, intertribal sexual hybridizations were carried out with B. rapa (2n = 20), and the resulting hybrids and their progenies were characterized.

METHODS

Using genomic in situ hybridization (GISH) and amplified fragment length polymorphism (AFLP), chromosomal/genomic components of the hybrids and their progenies were analysed.

KEY RESULTS

Many hybrid plants were obtained from the mature seeds harvested from the B. rapa x I. indigotica cross, and these exhibited different morphological traits. However, the majority of them did not survive and only three plants grew to maturity. These three hybrids showed poor growth and much smaller stature than the two parents, but had some morphological traits and chemical composition of I. indigotica. One plant had 2n = 10, the haploid chromosome number of B. rapa, and was absolutely sterile. The other two plants had 20 and 22 somatic chromosomes and were male sterile but produced seeds following pollinations with B. rapa. All back-cross progenies over several generations maintained a B. rapa-type phenotype and also displayed some variations in morphological characters and fatty acid compositions. They were all 2n = 20 and showed good seed-set. The hybrid with 2n = 22 produced some progeny plants with 2n = 21 and 2n = 22. GISH detected two chromosomes of I. indigotica in the hybrid with 2n = 22 but none in the one with 2n = 20. AFLP bands specific for I. indigotica, novel for two parents or absent in B. rapa, were detected in the two hybrids and their progenies. These progeny plants were novel B. rapa types with an altered genomic constitution or alien additions.

CONCLUSIONS

Complete or partial chromosome elimination and diploidization with genomic rearrangements were considered to lead to the formation of partial hybrids in this cross.

[Inheritance of plant height in hexaploid triticales with R/D substitution]

Inheritance of plant height has been studied in combinations of R/D-substituted forms of hexaploid triticale and specimens that have a complete chromosome set of rye and carry various genes determining dwarfism. Analysis of F1-F3 hybrids has demonstrated an additive effect of the dwarfism genes and the genetic component of chromosome D affecting the plant height. Deviations in the segregation with respect to plant height found in F2 combinations involving R/D-substituted forms and specimens with a complete chromosomal set of the R genome may be caused by meiotic disturbances resulting from the R/D substitution and an increase frequency of the transmission of the heterologous chromosome in the monosomically substituted form.

Partitioning of genetically distinct cell populations in chimeric juveniles of the sponge Amphimedon queenslandica

Natural chimerism, the fusion between genetically distinct conspecifics, is a process known to occur in various marine benthic invertebrates. Sponges (phylum Porifera) have proven to be a useful model to study the origin and evolution of allorecognition. Like some other invertebrates, they display an ontogenetic shift in their allorecognition response: genetically different individuals can fuse during early development, but, in most instances, not as adults. However, there is a limited understanding of the cellular organisation of sponge chimeras and the onset of this allorecognition response, which prevents integration of incompatible genotypes. Here we follow the behaviours and fates of cells derived from genetically distinct larvae of the demosponge Amphimedon queenslandica that have fused together at metamorphosis. By labelling individual larvae with different fluorescent dyes, we can follow cell movement in the postlarval chimeras. We observed that cells from the two individuals readily mixed for 2 weeks after the initial fusion. After that time, differently labelled cells began to sort into different postlarval cellular territories, with one lineage giving rise to choanocytes and the other to pinacocytes and cells of the mesohyl. These results suggest that a rapid ontogenetic shift in the allogeneic response of A. queenslandica occurs about 2 weeks after the initiation of metamorphosis and that the molecular basis of this response is also involved in creating differential cell affinities that underlie the construction of the sponge body plan. Compatible with this proposition is the observation that cells from postlarvae that are allowed to develop for 2 weeks before contact do not fuse and form a distinct boundary between genotypes. The successful chimeras remained stable for the duration of the experiment (3 weeks) raising the possibility that reproductive chimeras might persist in the natural environment, with a single genotype giving rise to germ cells.

[DNA methylation in cotton hybrids and their parents]

The possible role of methylation in the performance of heterosis has been analyzed in many crops. To further study this possibility, we investigated both the differences in cytosine methylation patterns between cotton heterotic hybrid/nonheterotic hybrids and their parental lines and the change in methylation level from seedling stage to flowering stage by using the methylation-sensitive amplified polymorphism (MSAP) method. The results showed that the number of demethylation loci in highly heterotic hybrids was greater that in lowly heterotic hybrids, and the level of DNA cytosine methylation in cotton at the seedling stage is higher than that at the flowering stage. The altered methylation patterns at low-copy genomic regions can be confirmed by DNA gel blot analysis. A total of 39 fragments that showed different methylation patterns were cloned and sequenced. The methylation status of these genes was modified differentially in hybrid and parents, suggesting that these genes might play a role in the performance of heterosis.

Induction and origin of adventitious shoots from chimeras of Brassica juncea and Brassica oleracea

The chimeras between tuber mustard (Brassica juncea) and red cabbage (B. oleracea) were artificially synthesized in our previous study. Adventitious shoots were induced from nodal segments and leaf discs of TCC (LI-LII-LIII, LI -the outmost layer of shoot apical meristem; LII -the middle layer; LIII -the innermost layer. T = Tuber mustard, C = Red cabbage) chimeras. The origin of the shoots was analyzed by histology and molecular biology. As a result, the frequency of adventitious shoot induction rose with the increase of BA in MS medium in the area of the nodes. However, there was no different induction frequency of adventitious shoots from nodal segment bases in media with different BA concentrations. Most adventitious shoots (clustered shoots) arising from the node area were TTT (Tuber mustard- Tuber mustard- Tuber mustard) and only 4 shoots were chimeras, which indicated that more shoots originated from LI than from LII and LIII. All shoots from nodal segment bases were CCC (Red cabbage-Red cabbage- Red cabbage), indicating that the shoots originated from LII or LII and LIII. There were significant differences in the regeneration rate in the margin of the leaf discs among the three combinations of BA and NAA. Most adventitious shoots from the margin of leaf discs were CCC but 2 out of 70 were chimeras, which indicated that more shoots originated from LII or LII and LIII than from LI. All chimeras obtained by regeneration were different from the original explant donor in type in the present study. The origin of the adventitious shoots varied with the site of origin on the donor plant, and could be multicellular and multihistogenic.

[Diploid hybrids between allotetraploid wild potato species Solanum acaule Bitt., S. stoloniferum Schltdl. and dihaploids of S. tuberosum L]

The possibility to obtain diploid hybrids by pollination of allotetraploid wild potato species Solanum acaule and S. stoloniferum plants with fertile pollen of S. tuberosum dihaploids was demonstrated for the first time. Dihaploid hybrids have arisen with comparatively high frequency (from 12.5 to 33.3%). They were characterized by high regularity of meiosis and high fertility. They easily crossed with S. tuberosum dihaploids, forming viable progeny. This seems prospective for effective introgression of valuable genetic gene pool of wild allotetraploid potato species in breeding material of S. tuberosum on the diploid level.

Genealogy, morphology and fitness of spontaneous hybrids between wild and cultivated chicory (Cichorium intybus)

Crop species are known to hybridize spontaneously with wild relatives, but few studies have characterized the performance of hybrids at various genealogies, life stages and environments. A group of cultivar-like individuals and potential hybrids were observed in a roadside population of wild chicory plants in Denmark. Seeds were collected from all reproductive plants and grown in a common garden experiment, and their morphological and genetic compositions were analysed. Intermediate plants were identified as hybrids and comprised various backcross and F(n) combinations. A genotypic hybrid index (HI), spanning from wild-like to cultivar-like, was highly correlated to a morphological index. Plant survival, growth and reproduction were evaluated and compared to the genotypic HI. Overall, cultivar-like and intermediate plants grew larger than wild-like plants, flowered longer, and produced more flowers and seeds. The common garden included a nutrient gradient. At higher nutrient levels, intermediate and cultivar-like plants produced more flowers and seeds than wild-like plants, whereas this effect was less pronounced at lower nutrient levels. During winter, small rodents consumed roots of cultivar-like and intermediate plants preferentially. Thus, cultivated and wild chicory are able to hybridize spontaneously, producing hybrid offspring of several generations that may reproduce more effectively than their wild parent, but herbivory and poor environmental conditions may negatively affect their fitness.

An evolutionary hybrid cellular automaton model of solid tumour growth

We propose a cellular automaton model of solid tumour growth, in which each cell is equipped with a micro-environment response network. This network is modelled using a feed-forward artificial neural network, that takes environmental variables as an input and from these determines the cellular behaviour as the output. The response of the network is determined by connection weights and thresholds in the network, which are subject to mutations when the cells divide. As both available space and nutrients are limited resources for the tumour, this gives rise to clonal evolution where only the fittest cells survive. Using this approach we have investigated the impact of the tissue oxygen concentration on the growth and evolutionary dynamics of the tumour. The results show that the oxygen concentration affects the selection pressure, cell population diversity and morphology of the tumour. A low oxygen concentration in the tissue gives rise to a tumour with a fingered morphology that contains aggressive phenotypes with a small apoptotic potential, while a high oxygen concentration in the tissue gives rise to a tumour with a round morphology containing less evolved phenotypes. The tissue oxygen concentration thus affects the tumour at both the morphological level and on the phenotype level.

In vitro reprogramming of fibroblasts into a pluripotent ES-cell-like state

Nuclear transplantation can reprogramme a somatic genome back into an embryonic epigenetic state, and the reprogrammed nucleus can create a cloned animal or produce pluripotent embryonic stem cells. One potential use of the nuclear cloning approach is the derivation of 'customized' embryonic stem (ES) cells for patient-specific cell treatment, but technical and ethical considerations impede the therapeutic application of this technology. Reprogramming of fibroblasts to a pluripotent state can be induced in vitro through ectopic expression of the four transcription factors Oct4 (also called Oct3/4 or Pou5f1), Sox2, c-Myc and Klf4. Here we show that DNA methylation, gene expression and chromatin state of such induced reprogrammed stem cells are similar to those of ES cells. Notably, the cells-derived from mouse fibroblasts-can form viable chimaeras, can contribute to the germ line and can generate live late-term embryos when injected into tetraploid blastocysts. Our results show that the biological potency and epigenetic state of in-vitro-reprogrammed induced pluripotent stem cells are indistinguishable from those of ES cells.

Viability and bar expression are negatively correlated in Oregon Wolfe Barley Dominant hybrids

The expression level of bar, which encodes phosphinothricin acetyltransferase (PAT), was correlated with the inviability of barley hybrids between 20 Golden Promise-derived transgenic lines (Ds-bar lines) and a specialized genetic marker stock, Oregon Wolfe Barley Dominant (OWBD). Each Ds-bar line was homozygous for a modified maize Ds element that encoded bar and that had been delivered via transposition to a unique location. All Ds-bar lines were viable and morphologically similar. Only four of the 20 hybrid populations were viable. The remaining populations died prior to producing seed. Phenotypic, enzyme-linked immunosorbent assay and quantitative reverse transcriptase-polymerase chain reaction analyses of these lines, and of lines from unrelated transformation events that also expressed bar, showed that viability was negatively correlated with bar expression. Analysis of crosses of a high-bar-expressing line with the OWB mapping population showed that the sensitivity of OWBD to PAT segregated as a single locus on chromosome 6HL. No sensitivity to PAT could be detected in several other lines and cultivars. OWBD has been shown to be genetically divergent from other germplasm groups within cultivated barley; therefore, the observed sensitivity may be peculiar to OWBD and thus would not impact generally on the utility of bar as a selectable marker or source of herbicide resistance in barley. Nevertheless, these results demonstrate the extent of allelic variability present in Hordeum vulgare, and suggest an additional variable for consideration when devising protocols for the transformation of Hordeum cultivars or landraces that are not known to be tolerant to PAT.

[Introgression of Aegilops genetic material into the genome of hexaploid triticale]

Cytological analysis of different meiosis stages was performed in F4 hybrids in comparison with the F1 hybrids obtained through crosses between the hexaploid triticale and genome-substitution forms of Aurolata (AABBUU) and Aurosis (AABBS(sh)S(sh)) wheat, in which D genome of common wheat Aurora was substituted for the genomes of Aegilops umbellulata and Ae. sharonensis, respectively. It was demonstrated that in F4 the level of bivalent conjugation was substantially higher than the expected one. However, the value of meiotic index in F4 hybrids was still small, pointing to incomplete process of the meiosis stabilization, specifically, of the stages following the metaphase I. Based on the data of morphological and biochemical analyses of the hybrids produced, the forms of triticale carrying some properties of the genus Aegilops, which were of interest for genetic and breeding studies, were isolated.