Biomedical subjects

U Lagercrantz

Publications and source records attributed to U Lagercrantz.

11 recordsLinked to original sources

PubMed2004

Mapping of quantitative trait loci (QTLs) affecting autumn freezing resistance and phenology in Salix.

Quantitative trait locus (QTL) analysis was performed at different time points during cold-acclimation of a tetraploid F(2 ) Salix pedigree. The pedigree ( n=92) was derived from a cross between a frost-susceptible diploid female clone 'Jorunn' ( Salix viminalis) and a frost resistant hexaploid male clone 'SW901290' ( Salix dasyclados). Freezing resistance, height growth increment and number of new leaves were assessed at days 0, 12, 20, 24, 31 and 42 of a short day-low temperature (SD-LT) hardening regime, while the initiation of shoot tip abscission and shoot tip abscission were measured daily. Height increment, dry-to-fresh weight ratio and number of new leaves were also measured in a replicated field trial. Freezing resistance was determined from electrolyte leakage of leaf tissues and from visual injuries on stem segments, after exposure to a predetermined freeze-thaw stress. Using a genetic map of the F(2) composed of 432 single-dose AFLP markers, a total of 19 genomic regions controlling freezing resistance (10) and phenological traits (9) before and during cold-acclimation (SD-LT) were identified. The magnitude of the phenotypic variation explained by each freezing resistance locus varied over acclimation time (0-45%), and there was no time point at which all the QTLs could be detected. The single QTL detected for non-acclimated freezing resistance did not reach significance at any time point during cold-acclimation, suggesting an independent genetic relationship between non-acclimated and acclimated resistance to freezing in Salix. Five of the loci associated with freezing resistance shared common intervals with loci controlling phenological traits. Of the 14 QTLs controlling autumn freezing resistance and/or phenological traits in the indoors experiment, six (43%) were associated with autumn phenology-related traits, i.e. height increment, dry-to-fresh weight ratio and number of new leaves, measured in the field. A major locus with multi-trait association in both indoor and outdoor experiments was detected.

Acclimatization↗

PubMed2003

Expression of Chia4-Pa chitinase genes during somatic and zygotic embryo development in Norway spruce (Picea abies): similarities and differences between gymnosperm and angiosperm class IV chitinases.

The developmental pathway of somatic embryogenesis in Norway spruce involves proliferation of proembryogenic masses (PEMs), PEM-to-somatic embryo transition and further development of the somatic embryos. It has previously been shown that extracellular signal molecules, including arabinogalactan proteins, lipo-chitooligosaccharides and chitinases, regulate somatic embryogenesis. The Chia4-Pa1 gene from Norway spruce is described here. The Chia4-Pa1 encodes a typical basic class IV chitinase, although the intron-exon organization of this gymnosperm chitinase is different from that in angiosperm class IV chitinases. The Chia4-Pa1 belongs to a small gene family with highly similar members, and the expression pattern of Chia4-Pa1 cannot be distinguished from that of other Chia4-Pa members. Upon withdrawal of plant growth regulators, i.e. during a treatment that stimulates PEM-to-somatic embryo transition and massive programmed cell death, a significant increase in transcription and translation of Chia4-Pa genes takes place. The expression pattern analysis revealed that Chia4-Pa genes are expressed in a subpopulation of proliferating cells and at the base of the somatic embryo. Furthermore, in seeds, Chia4-Pa genes are expressed in the megagametophyte in the single cell-layered zone surrounding the corrosion cavity. Taken together these results suggest that the Chia4-Pa expressing cells have a megagametophyte signalling function and that CHIA4-Pa stimulates programmed cell death and promotes PEM-to-somatic embryo transition.

Base Sequence↗

PubMed2003

Genetic mapping of sex-linked markers in Salix viminalis L.

A total of 88 selective primer combinations were screened using bulked males and females sampled from four families of Salix viminalis. A total of more than 1000 polymorphic fragments was obtained, of which only four cosegregated with sex. These four sex-linked markers were subsequently scored in individuals that were used for bulked sample preparation in additional individuals of the same families, and in individuals in other families. A pair of primers that amplified the sex-linked fragments was constructed from one of the sex-linked amplified fragment length polymorphism (AFLP) fragments. In hybridization of Southern blot filters with the sex-linked DNA fragments, the band was present in females and absent in males, but the opposite pattern of band segregation (a band found in males and no band in females) was never observed in either the AFLP or RFLP experiments. Two of the sex-linked markers were placed on a linkage map. They both map at the same location in a linkage group comprising other markers not segregating with sex. Our data suggest that a single locus governs the sex determination and that nonrecombining sex chromosomes are absent in S. viminalis. A close association was found between skewed sex ratio and segregation distortion at this locus.

Chromosome Mapping↗

PubMed2001

PaHB1 is an evolutionary conserved HD-GL2 homeobox gene expressed in the protoderm during Norway spruce embryo development.

In angiosperms, the protoderm or outer cell layer is the first tissue to differentiate in the embryo proper. In gymnosperms, it is not known whether a protoderm is defined and similarly differentiated. Here, we report a cDNA designated PaHB1 (for Picea abies Homeobox1), which is expressed during somatic embryogenesis in Norway spruce. PaHB1 exon/intron organization and its corresponding protein are highly similar to those of the HD-GL2 angiosperm counterparts. A phylogenetic analysis reveals that PaHB1 is strongly associated with one subclass consisting of protoderm/epiderm-specific genes. Moreover, PaHB1 expression switches from a ubiquitous expression in proembryogenic masses to an outer cell layer-specific localization during somatic embryo development. Ectopic expression of PaHB1 in somatic embryos leads to an early developmental block. The transformed embryos lack a smooth surface. These findings show that the PaHB1 expression pattern is highly analogous to angiosperm HD-GL2 homologues, suggesting similarities in the definition of the outer cell layer in seed plants.

Amino Acid Sequence↗

PubMed2001

Multiple flowering time QTLs within several Brassica species could be the result of duplicated copies of one ancestral gene.

Quantitative trait locus (QTL) analysis was used to study the evolution of genes controlling the timing of flowering in four Brassica genomes that are all extensively replicated. Comparative mapping showed that a chromosomal region from the top of Arabidopsis thaliana chromosome 5 corresponded to three homoeologous copies in each of the diploid species Brassica nigra, B. oleracea, and B. rapa and six copies in the amphidiploid B. juncea. QTLs were detected in two of the three replicated segments in each diploid genome and in three of the six replicated segments in B. juncea. These results indicate that, for the studied trait, multiple QTLs resulting from genome duplication is the rule rather than the exception. Brassica homologues to two candidate genes (CO and FLC) identified from the corresponding A. thaliana region were mapped. CO homologues mapped close to the QTL peaks in eight of nine QTLs, while FLC homologues mapped farther away in those cases where the mapping resolution allowed a comparison. Thus, our data are consistent with the hypothesis that all the major QTLs we detected in the different species of Brassica could be the result of duplicated copies of the same ancestral gene, possibly the ancestor of CO.

Arabidopsis Proteins↗

PubMed2000

Rapid evolution of the family of CONSTANS LIKE genes in plants.

A family of CONSTANS LIKE genes (COLs) has recently been identified in Arabidopsis thaliana and other plant species. CONSTANS, the first isolated member, is a putative zinc finger transcription factor that promotes the induction of flowering in A. thaliana in long photoperiods. Phylogenetic analysis of the COL family demonstrated that it is organized into a few distinct groups, some of which evolved before the divergence of gymnosperms and angiosperms. Molecular evolutionary analyses showed that COL genes within the Brassicaceae family evolve rapidly. The number of nonsynonymous substitutions was larger, and the ratio of nonsynonymous to synonymous substitutions was higher. The analysis also indicated that the rate of evolution is heterogeneous between different domains in the COL genes. The results support previous data indicating that plant regulatory genes evolve relatively fast and that the rate of evolution varies significantly between different regions of those genes. The rate of evolution of COL genes seems to have accelerated during later stages of evolution, possibly as an effect of frequent gene duplications.

Amino Acid Sequence↗

PubMed2000

Amphidiploid Brassica juncea contains conserved progenitor genomes.

To perform a detailed study of genome evolution in the natural Brassica amphidiploid B. juncea, we have constructed two linkage maps based on RFLP (restriction fragment length polymorphism) markers; one generated from a cross between a resynthesized B. juncea (a chromosome doubled interspecific B. rapa x B. nigra hybrid) and a natural B. juncea cultivar, the other from a cross between two B. juncea cultivars. By using a common cultivar in both crosses, the two maps could be unambiguously integrated. All loci exhibited disomic inheritance of parental alleles in the natural x resynthesized cross, showing that B. rapa chromosomes paired exclusively with their A-genome homologues in B. juncea and that B. nigra chromosomes likewise paired with their B-genome homologues. The maps derived from the two crosses were also perfectly collinear. Furthermore, these maps were collinear with maps of the diploid progenitor species (B. nigra and B. rapa) produced using the same set of RFLP probes. These data indicate that the genome of B. juncea has remained essentially unchanged since polyploid formation. Our observations appear to refute the suggestion that the formation of polyploid genomes is accompanied by rapid change in genome structure.

Brassica↗

PubMed1998

Comparative mapping between Arabidopsis thaliana and Brassica nigra indicates that Brassica genomes have evolved through extensive genome replication accompanied by chromosome fusions and frequent rearrangements.

Chromosome organization and evolution in the Brassicaceae family was studied using comparative linkage mapping. A total of 160 mapped Arabidopsis thaliana DNA fragments identified 284 homologous loci covering 751 cM in Brassica nigra. The data support that modern diploid Brassica species are descended from a hexaploid ancestor, and that the A. thaliana genome is similar in structure and complexity to those of each of the hypothetical diploid progenitors of the proposed hexaploid. Thus, the Brassica lineage probably went through a triplication after the divergence of the lineages leading to A. thaliana and B. nigra. These duplications were also accompanied by an exceptionally high rate of chromosomal rearrangements. The average length of conserved segments between A. thaliana and B. nigra was estimated at 8 cM. This estimate corresponds to approximately 90 rearrangements since the divergence of the two species. The estimated rate of chromosomal rearrangements is higher than any previously reported data based on comparative mapping. Despite the large number of rearrangements, fine-scale comparative mapping between model plant A. thaliana and Brassica crops is likely to result in the identification of a large number of genes that affect important traits in Brassica crops.

Arabidopsis↗

PubMed1996

Comparative mapping in Arabidopsis and Brassica, fine scale genome collinearity and congruence of genes controlling flowering time.

The model dicotyledonous plant, Arabidopsis thaliana, is closely related to Brassica crop species. It is intended that information concerning the genetic control of basic biological processes in Arabidopsis will be transferable to other species. Genome collinearity and its potential to facilitate the identification of candidate genes in Arabidopsis homologous to genes controlling important agronomic traits in Brassica was investigated. Genetic mapping in B. nigra identified two loci influencing flowering time (FT), with loci on linkage groups 2 and 8 explaining 53% and 12% of the total variation in FT, respectively. The CO gene exerts an important control over FT in A. thaliana, and B. nigra homologues of CO probably also play an important role in regulating FT. B. nigra homologues of CO were identified on linkage groups 2 and 8, the homologue on group 2 was coincident with the major locus controlling FT while the homologue on group 8 was within the 90% confidence interval of the weaker FT gene. The CO homologue on group 2 exhibits abundant allelic variation suggesting that it naturally controls a wide range of flowering times. Fine-scale A. thaliana/B. nigra comparative mapping demonstrated short-range collinearity between the genomes of Arabidopsis and Brassica. Eleven DNA fragments spaced over a 1.5 Mb contig in A. thaliana were used as RFLP probes in B. nigra. Three collinear representations of the A. thaliana contig were identified in B. nigra, with one interrupted by a large chromosomal inversion. Collinearity over this range will allow the resources generated by the Arabidopsis genome project to facilitate map-based cloning in Brassica crops.

Analysis of Variance↗

PubMed1996

Comparative genome mapping in Brassica.

A Brassica nigra genetic linkage map was developed from a highly polymorphic cross analyzed with a set of low copy number Brassica RFLP probes. The Brassica genome is extensively duplicated with eight distinct sets of chromosomal segments, each present in three copies, covering virtually the whole genome. Thus, B. nigra could be descended from a hexaploid ancestor. A comparative analysis of B. nigra, B. oleracea and B. rapa genomes, based on maps developed using a common set of RFLP probes, was also performed. The three genomes have distinct chromosomal structures differentiated by a large number of rearrangements, but collinear regions involving virtually the whole of each the three genomes were identified. The genic contents of B. nigra, B. oleracea and B. rapa were basically equivalent and differences in chromosome number (8, 9 and 10, respectively) are probably the result of chromosome fusions and/ or fissions. The strong conservation of overall genic content across the three Brassica genomes mirrors the conservation of genic content observed over a much longer evolutionary span in cereals. However, the rate of chromosomal rearrangement in crucifers is much higher than that observed in cereal genomes.

Brassica↗

PubMed1993

The abundance of various polymorphic microsatellite motifs differs between plants and vertebrates.

The abundance of different simple sequence motifs in plants was accessed through data base searches of DNA sequences and quantitative hybridization with synthetic dinucleotide repeats. Database searches indicated that microsatellites are five times less abundant in the genomes of plants than in mammals. The most common plant repeat motif was AA/TT followed by AT/TA and CT/GA. This group comprised about 75% of all microsatellites with a length of more than 6 repeats. The GT/CA motif being the most abundant dinucleotide repeat in mammals was found to be considerably less frequent in plants. To address the question if plant simple repeat sequences are variable as in mammals, (GT)n and (CT)n microsatellites were isolated from B.napus. Five loci were investigated by PCR-analysis and amplified products were obtained for all microsatellites from B. oleracea, B.napus and B.rapa DNA, but only for one primer pair from B.nigra. Polymorphism was detected for all microsatellites.

Animals↗