RESUMEN
Phenotypic plasticity is when one genome can produce more than one phenotype. The caste system found in many social insects is an important example of plasticity. Several studies have examined gene expression in social insect developmental and caste differences. Changes in gene expression, however, are not the only source of phenotypic plasticity. Here, we investigate the role of alternative splicing in the buff-tailed bumble bee Bombus terrestris. We found that 5,458 genes in B. terrestris (40%) express more than one isoform. Larvae have the lowest level of splicing events, followed by adults and then pupae. We found that when an isoform is expressed in a given caste in the larval stage, it tends to be expressed in all castes at the larval stage. The same is true at the pupal stage. However, we see more complicated interactions between the adult castes with reproductive females showing different isoform expression compared to nonreproductive females and male adults showing the most distinct patterns. We found 455 isoform switching genes, that is genes, where one developmental stage, sex or caste uses a specific isoform and another type uses a different isoform. Among genes displaying isoform switching are some involved in the ecdysteriod pathway, an important system in insect behaviour.
Asunto(s)
Adaptación Fisiológica/genética , Empalme Alternativo/genética , Abejas/genética , Abejas/fisiología , Animales , Abejas/crecimiento & desarrollo , Secuencia Conservada , Exones/genética , Femenino , Genes de Insecto , Jerarquia Social , Masculino , Dominios Proteicos , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Análisis de Secuencia de ADNRESUMEN
Appropriate allocation of resources to the offspring is critical for successful reproduction, particularly in species that reproduce on more than one occasion. The offspring must be provisioned adequately to ensure its vigour, whereas the parent must not become so depleted such that its survival is endangered. In both flowering plants and mammals specialised structures have evolved to support the offspring during its development. In this review we consider common themes that may indicate conservation of nutrient transfer function and regulation by genomic imprinting across the two kingdoms.
Asunto(s)
Endospermo/fisiología , Intercambio Materno-Fetal , Placenta/fisiología , Animales , Epigénesis Genética , Femenino , Impresión Genómica , Factor II del Crecimiento Similar a la Insulina/genética , Plantas/embriología , Plantas/genética , Embarazo , Fenómenos Fisiologicos de la Nutrición Prenatal , Regiones Promotoras Genéticas/genéticaRESUMEN
The reaction steps leading from the intermediate adenosine 5'-phosphosulfate (APS) to sulfide within the higher plant reductive sulfate assimilation pathway are the subject of controversy. Two pathways have been proposed: a 'bound intermediate' pathway in which the sulfo group of APS is first transferred by APS sulfotransferase to a carrier molecule to form a bound sulfite intermediate and is then further reduced by thiosulfonate reductase to bound sulfide; and a 'free intermediate' pathway in which APS is further activated to 3'-phosphoadenosine 5'-phosphosulfate (PAPS) by APS kinase followed by reduction of the sulfo group to free sulfite by PAPS reductase. Sulfite is then reduced to free sulfide by sulfite reductase. Sulfide, either free or bound, is then incorporated into organic form (as cysteine) by the enzyme O-acetylserine (thiol) lyase. In order to better characterize the pathway we attempted to clone PAPS reductase cDNAs by functional complementation of an Escherichia coli cysH mutant to prototrophy. We found no evidence for PAPS reductase cDNAs but did identify cDNAs that encode a small family of novel, chloroplast-localized proteins with APS reductase activity that are new members of the thioredoxin superfamily. We show here that the thioredoxin domain of these proteins is functional. We speculate that rather than proceeding via either of the pathways proposed above, reductive sulfate assimilation proceeds via the reduction of APS to sulfite by APS reductase and the subsequent reduction of sulfite to sulfide by sulfite reductase. In this scheme the product of the APS kinase reaction, PAPS, is not a direct intermediate in the pathway but rather acts as a substrate for sulfotransferase action and perhaps as a store of activated sulfate that can be returned to the pathway as APS via phosphohydrolase action on PAPS. Interactions between enzyme isoforms within the chloroplast stroma may bring about substrate channeling of APS and contribute to the partitioning of APS between sulfotransferase reactions on the one hand and the synthesis of cysteine and related metabolites via the reductive sulfate assimilation pathway on the other.
Asunto(s)
Oxidorreductasas actuantes sobre Donantes de Grupos Sulfuro , Oxidorreductasas/metabolismo , Plantas/enzimología , Sulfatos/metabolismo , Tiorredoxinas/metabolismo , Oxidación-Reducción , Oxidorreductasas/genética , Plantas/genética , Tiorredoxinas/genéticaRESUMEN
Three different cDNAs, Prh-19, Prh-26, and Prh-43 [3'-phosphoadenosine-5'-phosphosulfate (PAPS) reductase homolog], have been isolated by complementation of an Escherichia coli cysH mutant, defective in PAPS reductase activity, to prototrophy with an Arabidopsis thaliana cDNA library in the expression vector lambda YES. Sequence analysis of the cDNAs revealed continuous open reading frames encoding polypeptides of 465, 458, and 453 amino acids, with calculated molecular masses of 51.3, 50.5, and 50.4 kDa, respectively, that have strong homology with fungal, yeast and bacterial PAPS reductases. However, unlike microbial PAPS reductases, each PRH protein has an N-terminal extension, characteristic of a plastid transit peptide, and a C-terminal extension that has amino acid and deduced three-dimensional homology to thioredoxin proteins. Adenosine 5'-phosphosulfate (APS) was shown to be a much more efficient substrate than PAPS when the activity of the PRH proteins was tested by their ability to convert 35S-labeled substrate to acid-volatile 35S-sulfite. We speculate that the thioredoxin-like domain is involved in catalytic function, and that the PRH proteins may function as novel "APS reductase" enzymes. Southern hybridization analysis showed the presence of a small multigene family in the Arabidopsis genome. RNA blot hybridization with gene-specific probes revealed for each gene the presence of a transcript of approximately 1.85 kb in leaves, stems, and roots that increased on sulfate starvation. To our knowledge, this is the first report of the cloning and characterization of plant genes that encode proteins with APS reductase activity and supports the suggestion that APS can be utilized directly, without activation to PAPS, as an intermediary substrate in reductive sulfate assimilation.