Homospermidine synthase, the first pathway-specific enzyme of pyrrolizidine alkaloid biosynthesis, evolved from deoxyhypusine synthase. (1/55)

Pyrrolizidine alkaloids are preformed plant defense compounds with sporadic phylogenetic distribution. They are thought to have evolved in response to the selective pressure of herbivory. The first pathway-specific intermediate of these alkaloids is the rare polyamine homospermidine, which is synthesized by homospermidine synthase (HSS). The HSS gene from Senecio vernalis was cloned and shown to be derived from the deoxyhypusine synthase (DHS) gene, which is highly conserved among all eukaryotes and archaebacteria. DHS catalyzes the first step in the activation of translation initiation factor 5A (eIF5A), which is essential for eukaryotic cell proliferation and which acts as a cofactor of the HIV-1 Rev regulatory protein. Sequence comparison provides direct evidence for the evolutionary recruitment of an essential gene of primary metabolism (DHS) for the origin of the committing step (HSS) in the biosynthesis of pyrrolizidine alkaloids.  (+info)

Tansy ragwort poisoning in a horse in southern Ontario. (2/55)

Bizarre behavior, apparent lameness, and colic were noticed in 1 of 3 horses on a pasture overgrown by weeds during a drought. Liver failure and hepatoencephalopathy were diagnosed, caused by pyrrolizidine alkaloid toxicosis associated with consumption of tansy ragwort. The horse made a full recovery when removed from the pasture.  (+info)

The molecular basis of allergenicity: comparative analysis of the three dimensional structures of diverse allergens reveals a common structural motif. (3/55)

BACKGROUND: Although a large number of allergens have been characterised, the structural, functional, and biochemical features that these molecules have in common, and that could explain their ability to elicit powerful IgE antibody responses, are still uncertain. Recently, there has been considerable interest in the role of the cysteine protease activity of the house dust mite allergen Der p 1 in biasing the immune response in favour of IgE production. AIMS: To search for remote homologues of Der p 1 with sequences similar to the 30 conserved amino acids surrounding the catalytic cysteine residue (Cys34). METHODS: Potential homologues were analysed by examining their three dimensional structures and multiple sequence alignments using the programs PROPSEARCH, ClustalW, GeneDoc, and Swiss Pdb Viewer. RESULTS: Diverse allergens (for example, the plant cysteine protease papain, the transport protein lipocalin Mus m 1, and the ragweed allergen Amb a 5) have a similar structural motif; namely, a groove resembling the substrate binding groove of Der p 1. The groove is located inside an alpha-beta motif, between an alpha helix on one side and an antiparallel beta sheet on the other side. A similar common motif (a cysteine stabilised alpha-beta fold) can also be found in some toxins and defensins. CONCLUSION: Allergens of diverse sources have a common structural motif, namely a groove located inside an alpha-beta motif, which could potentially serve as a ligand binding site.  (+info)

The genetic basis of floral variation in Senecio jacobaea (Asteraceae). (4/55)

The self-incompatible composite Senecio jacobaea (ragwort) exhibits geographic variation in the frequency of rayed and discoid (rayless) individuals. Hybrid progenies from within- and between-morph crosses were established in a seminatural (garden) environment to determine whether patterns of segregation conform to single-gene predictions (as found in other Senecio species), whether the direction of dominance is conducive to rapid evolutionary change in ray morphology, and whether geographically distant populations of the discoid morph utilize the same or different genes to suppress ray development. Data from segregating F2 and BC families were consistent with a genetic model involving one major locus and an unknown number of modifiers. Analysis of F1 progenies from different intermorph crosses using the same rayed plant as a seed parent revealed a variable and incomplete pattern of dominance, with a trend toward partial dominance in some crosses. Hybridizations between discoid populations produced a few rayed progeny (4%), but there was no tendency for the frequency of rayed progeny to increase with the geographic distance separating the parent populations. Results of this study indicate that major mutations have been important for the evolution of discoid populations of ragwort, that ray-suppressing mutations should be directly available to selection in most populations, and that the suppression of rays is conditioned by the same or similar gene(s) in Atlantic and Baltic populations of the discoid taxon.  (+info)

Extinction of the Edinburgh lineage of the allopolyploid neospecies, Senecio cambrensis Rosser (Asteraceae). (5/55)

Senecio cambrensis is a new allopolyploid species, which originated independently in North Wales and in Edinburgh, Scotland. Despite extensive searches, the species has not been found growing at any of its previously recorded sites in Edinburgh or at other potential sites in the area since 1993. We have concluded that the Edinburgh lineage of S. cambrensis is now extinct and discuss possible causes of its extinction. The lineage was present in Edinburgh from at least 1974 and therefore survived in the wild for a minimum of 19 years. The species remains well established in parts of North Wales.  (+info)

Cell-specific expression of homospermidine synthase, the entry enzyme of the pyrrolizidine alkaloid pathway in Senecio vernalis, in comparison with its ancestor, deoxyhypusine synthase. (6/55)

Pyrrolizidine alkaloids (PAs) are constitutive plant defense compounds with a sporadic taxonomic occurrence. The first committed step in PA biosynthesis is catalyzed by homospermidine synthase (HSS). Recent evidence confirmed that HSS evolved by gene duplication from deoxyhypusine synthase (DHS), an enzyme involved in the posttranslational activation of the eukaryotic translation initiation factor 5A. To better understand the evolutionary relationship between these two enzymes, which are involved in completely different biological processes, we studied their tissue-specific expression. RNA-blot analysis, reverse transcriptase-PCR, and immunolocalization techniques demonstrated that DHS is constitutively expressed in shoots and roots of Senecio vernalis (Asteraceae), whereas HSS expression is root specific and restricted to distinct groups of endodermis and neighboring cortex cells located opposite to the phloem. All efforts to detect DHS by immunolocalization failed, but studies with promoter-beta-glucuronidase fusions confirmed a general expression pattern, at least in young seedlings of tobacco (Nicotiana tabacum). The expression pattern for HSS differs completely from its ancestor DHS due to the adaptation of HSS to the specific requirements of PA biosynthesis.  (+info)

Sporophytic self-incompatibility in Senecio squalidus L (Asteraceae)--the search for S. (7/55)

Senecio squalidus (Oxford Ragwort) is being used as a model species to study the genetics and molecular genetics of self-incompatibility (SI) in the Asteraceae. S. squalidus has a strong system of sporophytic SI (SSI) and populations within the UK contain very few S alleles probably due to a population bottleneck experienced on its introduction to the UK. The genetic control of SSI in S. squalidus is complex and may involve a second locus epistatic to S. Progress towards identifying the female determinant of SSI in S. squalidus is reviewed here. Research is focused on plants carrying two defined S alleles, S(1) and S(2). S(2) is dominant to S(1) in pollen and stigma. RT-PCR was used to amplify three SRK-like cDNAs from stigmas of S(1)S(2) heterozygotes, but the expression patterns of these cDNAs suggest that they are unlikely to be directly involved in SI or pollen-stigma interactions in contrast to SSI in the Brassicaceae. Stigma-specific proteins associated with the S(1) allele and the S(2) allele have been identified using isoelectric focusing and these proteins have been designated SSP1 (Stigma S-associated Protein 1) and SSP2. SSP1 and SSP2 cDNAs have been cloned by 3' and 5' RACE and shown to be allelic forms of the same gene, SSP. The expression of SSP and its linkage to the S locus are currently being investigated. Initial results show SSP to be expressed exclusively in stigmas and developmentally regulated, with maximal expression occurring at and just before anthesis when SI is fully functional, SSP expression being undetectable in immature buds. Together these data suggest that SSP is a strong candidate for a Senecio S-gene.  (+info)

The population genetics of sporophytic self-incompatibility in Senecio squalidus L. (Asteraceae) I: S allele diversity in a natural population. (8/55)

Twenty-six individuals of the sporophytic self-incompatible (SSI) weed, Senecio squalidus were crossed in a full diallel to determine the number and frequency of S alleles in an Oxford population. Incompatibility phenotypes were determined by fruit-set results and the mating patterns observed fitted a SSI model that allowed us to identify six S alleles. Standard population S allele number estimators were modified to deal with S allele data from a species with SSI. These modified estimators predicted a total number of approximately six S alleles for the entire Oxford population of S. squalidus. This estimate of S allele number is low compared to other estimates of S allele diversity in species with SSI. Low S allele diversity in S. squalidus is expected to have arisen as a consequence of a disturbed population history since its introduction and subsequent colonisation of the British Isles. Other features of the SSI system in S. squalidus were also investigated: (a) the strength of self-incompatibility response; (b) the nature of S allele dominance interactions; and (c) the relative frequencies of S phenotypes. These are discussed in view of the low S allele diversity estimates and the known population history of S. squalidus.  (+info)

• 1
• 2
• 3
• 4
• 5
• 6
• 7