Elucidation of molecular and hormonal background of early growth cessation and endodormancy induction in two contrasting Populus hybrid cultivars

BACKGROUND

Over the life cycle of perennial trees, the dormant state enables the avoidance of abiotic stress conditions. The growth cycle can be partitioned into induction, maintenance and release and is controlled by complex interactions between many endogenous and environmental factors. While phytohormones have long been linked with dormancy, there is increasing evidence of regulation by DAM and CBF genes. To reveal whether the expression kinetics of CBFs and their target PtDAM1 is related to growth cessation and endodormancy induction in Populus, two hybrid poplar cultivars were studied which had known differential responses to dormancy inducing conditions.

RESULTS

Growth cessation, dormancy status and expression of six PtCBFs and PtDAM1 were analyzed. The 'Okanese' hybrid cultivar ceased growth rapidly, was able to reach endodormancy, and exhibited a significant increase of several PtCBF transcripts in the buds on the 10th day. The 'Walker' cultivar had delayed growth cessation, was unable to enter endodormancy, and showed much lower CBF expression in buds. Expression of PtDAM1 peaked on the 10th day only in the buds of 'Okanese'. In addition, PtDAM1 was not expressed in the leaves of either cultivar while leaf CBFs expression pattern was several fold higher in 'Walker', peaking at day 1. Leaf phytohormones in both cultivars followed similar profiles during growth cessation but differentiated based on cytokinins which were largely reduced, while the Ox-IAA and iP7G increased in 'Okanese' compared to 'Walker'. Surprisingly, ABA concentration was reduced in leaves of both cultivars. However, the metabolic deactivation product of ABA, phaseic acid, exhibited an early peak on the first day in 'Okanese'.

CONCLUSIONS

Our results indicate that PtCBFs and PtDAM1 have differential kinetics and spatial localization which may be related to early growth cessation and endodormancy induction under the regime of low night temperature and short photoperiod in poplar. Unlike buds, PtCBFs and PtDAM1 expression levels in leaves were not associated with early growth cessation and dormancy induction under these conditions. Our study provides new evidence that the degradation of auxin and cytokinins in leaves may be an important regulatory point in a CBF-DAM induced endodormancy. Further investigation of other PtDAMs in bud tissue and a study of both growth-inhibiting and the degradation of growth-promoting phytohormones is warranted.

Genome-wide profiling of alternative splicing genes in hybrid poplar (P.alba×P.glandulosa cv.84K) leaves

Alternative splicing (AS) is a post-transcriptional process common in plants and essential for regulation of environmental fitness of plants. In the present study, we focus on the AS events in poplar leaves to understand their effects on plant growth and development. The hybrid poplar (P.alba×P.glandulosa cv.84K) leaves were collected for RNA extraction. The extracted RNA was sequenced using on an Illumina HiSeq™ 2000 platform. Using the Populus trichocarpa genome as the reference, a total of 3810 AS genes were identified (9225 AS events), which accounted for 13.51% of all the expressed genes. Intron retention was the most common AS event, accounting for 43.86% of all the AS events, followed by alternative 3′ splice sites (23.75%), alternative 5′ splice sites (23.71%), and exon skipping (8.68%). Chromosomes 10 had the most condensed AS events (33.67 events/Mb) and chromosome 19 had the least (12.42 events/Mb). Association analysis showed that AS in the poplar leaves was positively correlated with intron length, exon number, exon length, and gene expression level, and was negatively correlated with GC content. AS genes in the poplar leaves were associated mainly with inositol phosphate metabolism and phosphatidylinositol signaling system pathways that would be significant on wooden plant production.

Molecular investigations on a chimeric strain of Staphylococcus aureus sequence type 80

A PVL-positive, methicillin-susceptible Staphylococcus aureus was cultured from pus from cervical lymphadenitis of a patient of East-African origin. Microarray hybridisation assigned the isolate to clonal complex (CC) 80 but revealed unusual features, including the presence of the ORF-CM14 enterotoxin homologue and of an ACME-III element as well as the absence of etD and edinB. The isolate was subjected to both, Illumina and Nanopore sequencing allowing characterisation of deviating regions within the strain´s genome. Atypical features of this strain were attributable to the presence of two genomic regions that originated from other S. aureus lineages and that comprised, respectively, 3% and 1.4% of the genome. One deviating region extended from walJ to sirB. It comprised ORF-CM14 and the ACME-III element. A homologous but larger fragment was also found in an atypical S. aureus CC1/ST567 strain whose lineage might have served as donor of this genomic region. This region itself is a chimera comprising fragments from CC1 as well as fragments of unknown origin. The other deviating region comprised the region from htsB to ecfA2, i.e., another 3% of the genome. It was very similar to CC1 sequences. Either this suggests an incorporation of CC1 DNA into the study strain, or alternatively a recombination event affecting “canonical” CC80. Thus, the study strain bears witness of several recombination events affecting supposedly core genomic genes. Although the exact mechanism is not yet clear, such chimerism seems to be an additional pathway in the evolution of S. aureus. This could facilitate also a transmission of virulence and resistance factors and therefore offer an additional evolutionary advantage.

Ploidy Levels and Fitness-Related Traits in Purebreds and Hybrids Originating from Sterlet (Acipenser ruthenus) and Unusual Ploidy Levels of Siberian Sturgeon (A. baerii)

The present study aimed to investigate and compare fitness-related traits and ploidy levels of purebreds and hybrids produced from sturgeon broodstock with both normal and abnormal ploidy levels. We used diploid Acipenser ruthenus and tetraploid A. baerii males and females to produce purebreds and reciprocal hybrids of normal ploidy levels. Likewise, we used diploid A. ruthenus and tetraploid A. baerii females mated to pentaploid and hexaploid A. baerii males to produce hybrids of abnormal ploidy levels. Fertilization of ova of A. ruthenus and A. baerii of normal ploidy with the sperm of pentaploid and hexaploid A. baerii produced fully viable progeny with ploidy levels that were intermediate between those of the parents as was also found in crosses of purebreds and reciprocal hybrids of normal ploidy levels. The A. ruthenus × pentaploid A. baerii and A. ruthenus × hexaploid A. baerii hybrids did not survive after 22 days post-hatch (dph). Mean body weight and cumulative survival were periodically checked at seven-time intervals. The recorded values of mean body weight were significantly higher in A. baerii × pentaploid A. baerii hybrids than other groups at three sampling points (160, 252 and 330 dph). In contrast, the highest cumulative survival was observed in A. baerii × A. ruthenus hybrids at all sampling points (14.47 ± 5.70 at 497 dph). Overall, most of the studied sturgeon hybrids displayed higher mean BW and cumulative survival compared to the purebreds. The utilization of sturgeon hybrids should be restricted to aquaculture purposes because they can pose a significant genetic threat to native populations through ecological interactions.

Examination of Genomic and Transcriptomic Alterations in a Morphologically Stable Line, MU1, Generated by Intergeneric Pollination

Interspecific hybridization creates genetic variation useful for crop improvement. However, whether pollen from a different genus affects the genomic stability and/or transcriptome of the recipient species during intergeneric pollination has not been investigated. Here, we crossed japonica rice cv. Z12 with the maize accession B73 (pollen donor) and obtained a morphologically stable line, MU1, exhibiting moderate dwarfism, higher tiller number, and increased grain weight compared with Z12. To reveal the genetic basis of these morphological changes in MU1, we performed whole-genome resequencing of MU1 and Z12. Compared with Z12, MU1 showed 107,250 single nucleotide polymorphisms (SNPs) and 23,278 insertion/deletions (InDels). Additionally, 5'-upstream regulatory regions (5'UTRs) of 429 and 309 differentially expressed genes (DEGs) in MU1 contained SNPs and InDels, respectively, suggesting that a subset of these DEGs account for the variation in 5'UTRs. Transcriptome analysis revealed 2190 DEGs in MU1 compared with Z12. Genes up-regulated in MU1 were mainly involved in photosynthesis, generation of precursor metabolites, and energy and cellular biosynthetic processes; whereas those down-regulated in MU1 were involved in plant hormone signal transduction pathway and response to stimuli and stress processes. Quantitative PCR (qPCR) further identified the expression levels of the up- or down-regulated gene in plant hormone signal transduction pathway. The expression level changes of plant hormone signal transduction pathway may be significant for plant growth and development. These findings suggest that mutations caused by intergeneric pollination could be the important reason for changes of MU1 in agronomic traits.

Macronutrients influence yield and oil quality of hybrid maize (Zea mays L.)

In the present two-year study, an attempt was made to estimate the grain yield, grain nutrient uptake, and oil quality of three commonly grown maize (Zea mays L.) hybrids fertilized with varied levels of nitrogen (N), phosphorus (P) and potassium (K). Results obtained from both the experimental years indicated that application of 125% of recommended dose of fertilizer (RDF) recorded maximum grain yield (10.37 t ha-1; 124% higher than control). When compared with 100% RDF, grain yield reduction with nutrient omission was 44% for N omission, 17% for P omission, and 27% for K omission. Nitrogen uptake was increased with increasing NPK levels up to 150% RDF that was statistically at par (p ≥ 0.01) with 125% RDF. Increasing trend in P and K uptake was observed with successive increase in NPK levels up to 125% RDF, above which it declined. The protein content was significantly higher in grains of var. P 3396 with 125% RDF. Nutrient management has significant (p ≤ 0.01) role in the grain oil content. Saturated fatty acids (palmitic, stearic and arachidic acid) content decreased, and unsaturated fatty acid (oleic, linoleic and linolenic acid) increased with increasing NPK levels. The average oleic acid desaturation and linoleic acid desaturation ratios were increased with increasing NPK levels up to 100 and 125% RDF, respectively. However, average monounsaturated fatty acids (MUFA): poly-unsaturated fatty acids (PUFA), saturated: unsaturated as well as linoleic: linolenic acid ratios were increased on receiving 75% RDF, and beyond that it showed decreasing trend. The omission of K had the highest inhibitory effect on corn oil quality followed by N and P omission.

Production of Transgenic Chickens Using Cultured Primordial Germ Cells and Gonocytes

The unique characteristics of the avian embryo, with its large opaque yolk, have necessitated the development of different approaches to transgenesis from those that have been successful in mammalian species. Genetic modification of birds was greatly advanced by the ability to grow long-term cultures of primordial germ cells (PGCs). These cells are obtained from embryos, established in culture, and can be propagated without losing the ability to contribute to the germline when reintroduced into a host animal. PGCs can be genetically modified in culture using traditional transfection and selection techniques, including gene targeting and site-specific nuclease approaches. Here, we describe our methods for deriving cell lines, long-term culture, genetic modification, production of germline chimeras and obtaining fully transgenic birds with the desired genetic modifications.

Twin Inc

This paper presents an account of how human spontaneous embryonic chimeras are formed. On the prevalent view in the philosophical literature, it is said that chimeras are the product of two embryos that fuse to form a new third embryo. We call this version of fusion synthesis. In contrast to synthesis, we present an alternative mechanism for chimera formation called incorporation, wherein one embryo incorporates the cells of a second embryo into its body. We argue that the incorporation thesis explains other types of chimera formation, which are better understood, and is more consistent than synthesis with what is known about embryological development. Incorporation also has different implications than synthesis and so avoids the philosophical puzzles that are often said to accompany embryonic chimera formation-puzzles which pose problems to the human embryo's persistence from fertilization to the fetal stage of human development.

Differentially abundant proteins associated with heterosis in the primary roots of popcorn

Although heterosis has significantly contributed to increases in worldwide crop production, the molecular mechanisms regulating this phenomenon are still unknown. In the present study, we used a comparative proteomic approach to explore hybrid vigor via the proteome of both the popcorn L54 ♀ and P8 ♂ genotypes and the resultant UENF/UEM01 hybrid cross. To analyze the differentially abundant proteins involved in heterosis, we used the primary roots of these genotypes to analyze growth parameters and extract proteins. The results of the growth parameter analysis showed that the mid- and best-parent heterosis were positive for root length and root dry matter but negative for root fresh matter, seedling fresh matter, and protein content. The comparative proteomic analysis identified 1343 proteins in the primary roots of hybrid UENF/UEM01 and its parental lines; 220 proteins were differentially regulated in terms of protein abundance. The mass spectrometry proteomic data are available via ProteomeXchange with identifier “PXD009436”. A total of 62 regulated proteins were classified as nonadditive, of which 53.2% were classified as high parent abundance (+), 17.8% as above-high parent abundance (+ +), 16.1% as below-low parent abundance (− −), and 12.9% as low parent abundance (-). A total of 22 biological processes were associated with nonadditive proteins; processes involving translation, ribosome biogenesis, and energy-related metabolism represented 45.2% of the nonadditive proteins. Our results suggest that heterosis in the popcorn hybrid UENF/UEM01 at an early stage of plant development is associated with an up-regulation of proteins related to synthesis and energy metabolism.

Prevalence of twin foaling and blood chimaerism in purebred Spanish horses

Twin foaling is associated with chimaerism in several domestic species and is recognised in horses. In this study, 21,097 purebred Spanish (Pura Raza Español) horse births from the 2015 to 2016 breeding season were investigated for chimaerism. Twin foaled and chimaeric individuals were assessed on the basis of foaling records, short-tandem repeat (STR) parentage test results and a sex-linked STR-based technique. Fourteen twin pregnancies with 23 twin foals born alive were identified (0.066% twin foaling prevalence), including five blood chimaeric cases (21.7%; overall prevalence 0.011%), suggesting that this genetic condition is extremely low in horses. Furthermore, no true chimaeras were detected. This is the first large scale study analysing the occurrence of chimaerism in a horse population and the first assessment of twin foaling in purebred Spanish horses.

Identification of Metabolism and Excretion Differences of Procymidone between Rats and Humans Using Chimeric Mice: Implications for Differential Developmental Toxicity

A metabolite of procymidone, hydroxylated-PCM, causes rat-specific developmental toxicity due to higher exposure to it in rats than in rabbits or monkeys. When procymidone was administered to chimeric mice with rat or human hepatocytes, the plasma level of hydroxylated-PCM was higher than that of procymidone in rat chimeric mice, and the metabolic profile of procymidone in intact rats was well reproduced in rat chimeric mice. In human chimeric mice, the plasma level of hydroxylated-PCM was less, resulting in a much lower exposure. The main excretion route of hydroxylated-PCM-glucuronide was bile (the point that hydroxylated-PCM enters the enterohepatic circulation) in rat chimeric mice, and urine in human chimeric mice. These data suggest that humans, in contrast to rats, extensively form the glucuronide and excrete it in urine, as do rabbits and monkeys. Overall, procymidone's potential for causing teratogenicity in humans must be low compared to that in rats.

PzTAC and PzLAZY from a narrow-crown poplar contribute to regulation of branch angles

Plant architecture, as a basic element influenced by genetic and environmental factors, has an important effect on grain yield via light transmission in agroforestry systems. The molecular mechanism underlying control of branch angle, an important aspect of tree architecture, is not well understood in poplars. Here, we cloned two genes from Populus × zhaiguanheibaiyang (a narrow-crown poplar), designated PzTAC and PzLAZY, which were predicted to be members of the ITG gene family through sequence homology. Transcript levels of the homologous genes were estimated by reverse transcriptase quantitative PCR (RT-qPCR) in different organs of P. × zhaiguanheibaiyang and P. Deltoides 'Zhonglin2025' (a broad-crown poplar). TAC expression was mainly confined to the leaves and annual shoots, whereas LAZY was mainly expressed in the annual shoots and axillary buds. Beside, we detected the promoter expression patterns derived from the PzTAC and PzLAZY genes using the β-glucuronidase (GUS) reporter gene in transgenic Populus × euramericana 'Neva'. GUS activity driven by the PzTAC and PzLAZY promoters was detected in mature leaves, leaf axils and vascular tissues of roots. The PzTAC promoter was mainly active in leaf veins, whereas the PzLAZY promoter was mainly active in mesophyll cells and root tips. The average branch angle in transgenic 35S::PzTAC plants was larger than that of transgenic 35S::PzLAZY plants. The results provide strong evidence that the two genes affect the vascular tissues of transgenic plants to modify branch angles.

Seedling development in maize cv. B73 and blue light-mediated proteomic changes in the tip vs. stem of the coleoptile

In 2009, the draft genome of the reference inbred line of maize (Zea mays L. spp. mays cv. B73) was published so that, using this specific corn variety, molecular analyses of physiological processes became possible. However, the morphology and developmental patterns of B73 maize, compared with that of the more frequently used hybrid varieties, have not yet been analyzed. Here, we describe organ development in seedlings of B73 maize and in those of six other hybrid cultivars, and document significant morphological as well as quantitative differences between these varieties of Z. mays. In a second set of experiments, we used etiolated seedlings of B73 maize to analyze the effect of blue light (BL) on the patterns of proteins in the tip vs. growing region of this sheath-like organ. By using two-dimensional difference gel electrophoresis (2D DIGE), coupled with tandem mass spectrometry, we detected, in the microsomal fraction of maize coleoptile tips, rapid changes in the abundance of protein spots of maize phototropin 1 and several metabolic enzymes. In the sub-apical (growing) region of the coleoptile, proteomic changes were less pronounced. These results suggest that the tip of the coleoptile of B73 maize may serve as a unique model system for dissecting BL responses in a light-sensitive plant organ of known function.

Identification of heterotic loci associated with grain yield and its components using two CSSL test populations in maize

Heterosis has widely been used to increase grain yield and quality. In this study, the genetic basis of heterosis on grain yield and its main components in maize were examined over 2 years in two locations in two test populations constructed from a set of 184 chromosome segment substitution lines (CSSLs) and two inbred lines (Zheng58 and Xun9058). Of the 169 heterotic loci (HL) associated with grain yield and its five components identified in CSSL × Zheng58 and CSSL × Xun9058 test populations, only 25 HL were detected in both populations. The comparison of quantitative trait loci (QTLs) detected in the CSSL population with HL detected in the two test populations revealed that only 15.46% and 17.35% of the HL in the given populations respectively, shared the same chromosomal regions as that of the corresponding QTLs and showed dominant effects as well as pleiotropism with additive and dominant effects. In addition, most of the HL (74.23% and 74.49%) had overdominant effects. These results suggest that overdominance is the main contributor to the effects of heterosis on grain yield and its components in maize, and different HL are associated with heterosis for different traits in different hybrids.

Ploidy influences the functional attributes of de novo lager yeast hybrids

The genomes of hybrid organisms, such as lager yeast (Saccharomyces cerevisiae × Saccharomyces eubayanus), contain orthologous genes, the functionality and effect of which may differ depending on their origin and copy number. How the parental subgenomes in lager yeast contribute to important phenotypic traits such as fermentation performance, aroma production, and stress tolerance remains poorly understood. Here, three de novo lager yeast hybrids with different ploidy levels (allodiploid, allotriploid, and allotetraploid) were generated through hybridization techniques without genetic modification. The hybrids were characterized in fermentations of both high gravity wort (15 °P) and very high gravity wort (25 °P), which were monitored for aroma compound and sugar concentrations. The hybrid strains with higher DNA content performed better during fermentation and produced higher concentrations of flavor-active esters in both worts. The hybrid strains also outperformed both the parent strains. Genome sequencing revealed that several genes related to the formation of flavor-active esters (ATF1, ATF2¸ EHT1, EEB1, and BAT1) were present in higher copy numbers in the higher ploidy hybrid strains. A direct relationship between gene copy number and transcript level was also observed. The measured ester concentrations and transcript levels also suggest that the functionality of the S. cerevisiae- and S. eubayanus-derived gene products differs. The results contribute to our understanding of the complex molecular mechanisms that determine phenotypes in lager yeast hybrids and are expected to facilitate targeted strain development through interspecific hybridization.

Selection and dynamics of embryonic stem cell integration into early mouse embryos

The process by which pluripotent cells incorporate into host embryos is of interest to investigate cell potency and cell fate decisions. Previous studies suggest that only a minority of the embryonic stem cell (ESC) inoculum contributes to the adult chimaera. How incoming cells are chosen for integration or elimination remains unclear. By comparing a heterogeneous mix of undifferentiated and differentiating ESCs (serum/LIF) with more homogeneous undifferentiated culture (2i/LIF), we examine the role of cellular heterogeneity in this process. Time-lapse ex vivo imaging revealed a drastic elimination of serum/LIF ESCs during early development in comparison with 2i/LIF ESCs. Using a fluorescent reporter for naive pluripotency (Rex1-GFP), we established that the acutely eliminated serum/LIF ESCs had started to differentiate. The rejected cells were apparently killed by apoptosis. We conclude that a selection process exists by which unwanted differentiating cells are eliminated from the embryo. However, occasional Rex1(-) cells were able to integrate. Upregulation of Rex1 occurred in a proportion of these cells, reflecting the potential of the embryonic environment to expedite diversion from differentiation priming to enhance the developing embryonic epiblast.

A New Synthetic Amphiploid (AADDAA) between Gossypium hirsutum and G. arboreum Lays the Foundation for Transferring Resistances to Verticillium and Drought

Gossypium arboreum, a cultivated cotton species (2n = 26, AA) native to Asia, possesses invaluable characteristics unavailable in the tetraploid cultivated cotton gene pool, such as resistance to pests and diseases and tolerance to abiotic stresses. However, it is quite difficult to transfer favorable traits into Upland cotton through conventional methods due to the cross-incompatibility of G. hirsutum (2n = 52, AADD) and G. arboreum. Here, we improved an embryo rescue technique to overcome the cross-incompatibility between these two parents for transferring favorable genes from G. arboreum into G. hirsutum. Our results indicate that MSB2K supplemented with 0.5 mgl^-1 kinetin and 250 mg^-1 casein hydrolysate is an efficient initial medium for rescuing early (3 d after pollination) hybrid embryos. Eight putative hybrids were successfully obtained, which were further verified and characterized by cytology, molecular markers and morphological analysis. The putative hybrids were subsequently treated with different concentrations of colchicine solution to double their chromosomes. The results demonstrate that four putative hybrid plants were successfully chromosome-doubled by treatment with 0.1% colchicine for 24 h and become amphiploid, which were confirmed by cytological observation, self-fertilization and backcrossing. Preliminary assessments of resistance at seedling stage indicate that the synthetic amphiploid showed highly resistant to Verticillium and drought. The synthetic amphiploid between G. hirsutum × G. arboreum would lay the foundation for developing G. arboreum-introgressed lines with the uniform genetic background of G. hirsutum acc TM-1, which would greatly enhance and simplify the mining, isolation, characterization, cloning and use of G. arboreum-specific desirable genes in future cotton breeding programs.

[Analysis of wheat and rye semidwarfing gene distribution in spring hexaploid triticale (Triticosecale Wittm.) varieties and lines]

A collection of spring hexaploid triticale varieties and promising breeding lines has been examined for the presence of wheat Rht-B1b, Rht-B1e, and Rht8c semidwarfing genes and the rye Hl semidwarfing gene. It was discovered in spring triticale that these semidwarfing genes are represented by only one, the Rht-B1b wheat gene. The presence of this gene is associated with shortening of spring triticale plants by 28 cm on average, which constituted 26% of their initial height. Rht-B1b was found in all of the studied commercial varieties of spring triticale, which rendered it possible to conclude that plant height reduction is a necessary condition for increasing the competitiveness of this crop culture.

[Experimental hybridization of voies of the genus Microtus s.l. M. socialis with species of the group arvalis (Mammalia, Rodentia)]

The results of interspecific crosses of the social vole Microtus socialis with the Altai vole M. obscurus, the East European vole M. rossiaemeridionalis, and the Transcaspian vole M. transcaspicus are presented. The role of the sperm head structure in the reproductive isolation of this species was studied. Hybrids were obtained in five of the six crossing combinations. It is established that significant differences in the sperm head shape in the social vole and in arvalis group species do not prevent fertilization. The sterility of hybrids indicates the existence of postcopulative mechanisms of reproductive isolation.

Optimizing hill seeding density for high-yielding hybrid rice in a single rice cropping system in South China

Mechanical hill direct seeding of hybrid rice could be the way to solve the problems of high seeding rates and uneven plant establishment now faced in direct seeded rice; however, it is not clear what the optimum hill seeding density should be for high-yielding hybrid rice in the single-season rice production system. Experiments were conducted in 2010 and 2011 to determine the effects of hill seeding density (25 cm×15 cm, 25 cm×17 cm, 25 cm×19 cm, 25 cm×21 cm, and 25 cm×23 cm; three to five seeds per hill) on plant growth and grain yield of a hybrid variety, Nei2you6, in two fields with different fertility (soil fertility 1 and 2). In addition, in 2012 and 2013, comparisons among mechanical hill seeding, broadcasting, and transplanting were conducted with three hybrid varieties to evaluate the optimum seeding density. With increases in seeding spacing from 25 cm×15 cm to 25 cm×23 cm, productive tillers per hill increased by 34.2% and 50.0% in soil fertility 1 and 2. Panicles per m² declined with increases in seeding spacing in soil fertility 1. In soil fertility 2, no difference in panicles per m² was found at spacing ranging from 25 cm×17 cm to 25 cm×23 cm, while decreases in the area of the top three leaves and aboveground dry weight per shoot at flowering were observed. Grain yield was the maximum at 25 cm×17 cm spacing in both soil fertility fields. Our results suggest that a seeding density of 25 cm×17 cm was suitable for high-yielding hybrid rice. These results were verified through on-farm demonstration experiments, in which mechanical hill-seeded rice at this density had equal or higher grain yield than transplanted rice.

Early growth and development of reciprocal hybrids of the starry flounder Platichthys stellatus and stone flounder Kareius bicoloratus

Larval growth and development of hybrid flounder were observed and compared with those of their parent species. The reciprocal hybrids of female starry flounder Platichthys stellatus and male stone flounder Kareius bicoloratus (hybrid Sb) and of female K. bicoloratus and male P. stellatus (hybrid Bs) both survived and grew to juveniles. Development was divided into nine stages (A-I). Many of the hybrids' traits were identical and intermediate to those of their parents. The position of the eye, however, was primarily sinistral in both hybrids (80% in Sb and 76% in Bs), a trait possessed by P. stellatus (80%) in the western Pacific Ocean. The daily growth rates of the larvae were similar. In the parent species, development was more rapid in P. stellatus than in K. bicoloratus whereas rate of development was intermediate in both Sb and Bs hybrids. The size at settlement [standard length (LS ) at stage H (mean ± s.d.)] was 9·82 ± 1·47 mm for the hybrid Sb and 9·99 ± 0·90 mm for the hybrid Bs, while the minimum age at metamorphosis (initial age at stage H) was 29 days after hatching (DAH) in both hybrids. In comparison, LS at settlement in parent species was 6·43 ± 0·25 mm for P. stellatus and 12·87 ± 1·29 mm for K. bicoloratus. Minimum age at metamorphosis for the parents was 23 DAH at stage G in P. stellatus and 34 DAH at stage H in K. bicoloratus. Thus, the timing of settlement of hybrids was different from that of their parent species. These traits may occur with high frequency in a natural habitat.

Genotypic variability for antioxidant and quality parameters among tomato cultivars, hybrids, cherry tomatoes and wild species

BACKGROUND

Wide germplasm diversity and transferability of antioxidant parameters is the primary requirement for the development of high-antioxidant tomato cultivars. The present study was conducted to screen tomato genotypes including hybrids, varieties, cherry tomatoes, wild species, elite germplasm lines, interspecific hybrids and backcross populations for antioxidant activity and other quality parameters to select high-antioxidant lines with good total soluble solids (TSS) for further usage in crop improvement programmes.

RESULTS

Wild species and interspecific hybrids between LA-1777 (Solanum habrochaites) and an elite genotype 15SBSB recorded very high antioxidant capacity (FRAP), DPPH radical-scavenging ability, and high phenols and flavonoids. Interspecific hybrids also recorded very high total soluble solids (TSS). Significantly higher total carotenoids, lycopene and vitamin C were observed in IIHR-249-1 with moderately higher TSS. Cherry tomato lines IIHR-2866, 2865 and 2864 recorded four to five times more β-carotene than commercial hybrids/varieties.

CONCLUSION

Tomato line IIHR-249-1 can be used for improving antioxidant capacity, total carotenoids and lycopene in tomato breeding programmes. Cherry tomato lines IIHR-2866, 2865 and 2864 can be used for improving β-carotene content. LA-1777 and interspecific hybrids could be used for developing tomato lines rich in antioxidants as well as TSS.

[Effect of Triton X-100 on genetic segregation and associated monocotyledonous and dicotyledonous traits in sugarbeet (Beta vulgaris L.)]

The effect of Triton X-100 (TX-100) on the ratio of phenotypic classes and the expression of morphological traits in the progeny of sugar beet hybrids (N12 and N2) was investigated. It was shown that the TX-100 exposition on the unopened flower buds of sugar beets has different effects on hybrid progenies. In agamospermic progeny of hybrid plant No 12km-4, a significant decrease in the heteroallelic (heterozygous) phenotypic classes of alcohol dehydrogenase (ADH1) fraction was determined in the nonagamospermic progeny of hybrid plant No 2km-2 appearance of sugar beet seedlings with one cotyledon leaf was detected. The obtained results indicate the high efficiency of the epimutagenic effect of TX-100 on the early stages of plant ontogenesis.

Derivation of a germline competent transgenic Fischer 344 embryonic stem cell line

Embryonic stem (ES) cell-based gene manipulation is an effective method for the generation of mutant animal models in mice and rats. Availability of germline-competent ES cell lines from inbred rat strains would allow for creation of new genetically modified models in the desired genetic background. Fischer344 (F344) males carrying an enhanced green fluorescence protein (EGFP) transgene were used as the founder animals for the derivation of ES cell lines. After establishment of ES cell lines, rigorous quality control testing that included assessment of pluripotency factor expression, karyotype analysis, and pathogen/sterility testing was conducted in selected ES cell lines. One male ES cell line, F344-Tg.EC4011, was further evaluated for germline competence by injection into Dark Agouti (DA) X Sprague Dawley (SD) blastocysts. Resulting chimeric animals were bred with wild-type SD mates and germline transmissibility of the ES cell line was confirmed by identification of pups carrying the ES cell line-derived EGFP transgene. This is the first report of a germline competent F344 ES cell line. The availability of a new germline competent ES cell line with a stable fluorescence reporter from an inbred transgenic rat strain provides an important new resource for genetic manipulations to create new rat models.

Green revolution trees: semidwarfism transgenes modify gibberellins, promote root growth, enhance morphological diversity, and reduce competitiveness in hybrid poplar

Semidwarfism has been used extensively in row crops and horticulture to promote yield, reduce lodging, and improve harvest index, and it might have similar benefits for trees for short-rotation forestry or energy plantations, reclamation, phytoremediation, or other applications. We studied the effects of the dominant semidwarfism transgenes GA Insensitive (GAI) and Repressor of GAI-Like, which affect gibberellin (GA) action, and the GA catabolic gene, GA 2-oxidase, in nursery beds and in 2-year-old high-density stands of hybrid poplar (Populus tremula × Populus alba). Twenty-nine traits were analyzed, including measures of growth, morphology, and physiology. Endogenous GA levels were modified in most transgenic events; GA(20) and GA(8), in particular, had strong inverse associations with tree height. Nearly all measured traits varied significantly among genotypes, and several traits interacted with planting density, including aboveground biomass, root-shoot ratio, root fraction, branch angle, and crown depth. Semidwarfism promoted biomass allocation to roots over shoots and substantially increased rooting efficiency with most genes tested. The increased root proportion and increased leaf chlorophyll levels were associated with changes in leaf carbon isotope discrimination, indicating altered water use efficiency. Semidwarf trees had dramatically reduced growth when in direct competition with wild-type trees, supporting the hypothesis that semidwarfism genes could be effective tools to mitigate the spread of exotic, hybrid, and transgenic plants in wild and feral populations.

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.