Lipid metabolism in the moss Rhytidiadelphus squarrosus (Hedw.) Warnst. from lead-contaminated and non-contaminated populations.
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Lipid metabolism and the effect of Pb(2+) and Cu(2+) on this process was studied in the moss Rhytidiadelphus squarrosus collected from both a lead-contaminated and a non-contaminated site. Total radiolabelling of lipids from [1-(14)C]acetate was similar in both populations and Cu or Pb (1 microM, 10 microM) did not cause much alteration in acute exposure experiments. However, there were significant qualitative changes. Of the major labelled neutral lipid classes, samples from the lead-polluted site showed a decrease in labelling of triacylglycerols and an increase in wax esters. Acute lead exposure caused similar effects. Cu caused a decrease in the labelling of wax esters and an increase in diacylglycerols. These data suggest that heavy metals cause a change in carbon flux through the acylation reactions associated with the Kennedy pathway. R. squarrosus obtained from the Pb-contaminated site also showed changes in polar lipid labelling compared to the uncontaminated site. The labelling of phosphatidylcholine was more than halved and replaced by increased labelling of other zwitterionic lipids. The chloroplast glycerolipids were also increasingly labelled. Acute exposure to Pb, however, caused little alteration of labelling patterns within 24 h. R. squarrosus contains high levels of polyunsaturated fatty acids (PUFAs), but moss obtained from the Pb-polluted site had significantly less PUFAs containing three or more double bonds. Such samples, when incubated with [1-(14)C]acetate also showed decreased PUFA labelling. By contrast, acute exposure to Pb produced different results. These data provide a foundation for examining lipid metabolism in bryophytes and the effects of pollution in this important class of organism. The results also emphasize that acute and chronic exposure to heavy metals may produce different effects and that caution must be exercised in extrapolating data from one system to another. (+info)
The organization of Physcomitrella patensRAD51 genes is unique among eukaryotic organisms.
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Genetic recombination pathways and genes are well studied, but relatively little is known in plants, especially in lower plants. To study the recombination apparatus of a lower land plant, a recombination gene well characterized particularly in yeast, mouse, and man, the RAD51 gene, was isolated from the moss Physcomitrella patens and characterized. Two highly homologous RAD51 genes were found to be present. Duplicated RAD51 genes have been found thus far exclusively in eukaryotes with duplicated genomes. Therefore the presence of two highly homologous genes suggests a recent genome duplication event in the ancestry of Physcomitrella. Comparison of the protein sequences to Rad51 proteins from other organisms showed that both RAD51 genes originated within the group of plant Rad51 proteins. However, the two proteins form a separate clade in a phylogenetic tree of plant Rad51 proteins. In contrast to RAD51 genes from other multicellular eukaryotes, the Physcomitrella genes are not interrupted by introns. Because introns are a common feature of Physcomitrella genes, the lack of introns in the RAD51 genes is unusual and may indicate the presence of an unusual recombination apparatus in this organism. The presence of duplicated intronless RAD51 genes is unique among eukaryotes. Studies of further members of this lineage are needed to determine whether this feature may be typical of lower plants. (+info)
Cryptochrome light signals control development to suppress auxin sensitivity in the moss Physcomitrella patens.
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The blue light receptors termed cryptochromes mediate photomorphological responses in seed plants. However, the mechanisms by which cryptochrome signals regulate plant development remain obscure. In this study, cryptochrome functions were analyzed using the moss Physcomitrella patens. This moss has recently become known as the only plant species in which gene replacement occurs at a high frequency by homologous recombination. Two cryptochrome genes were identified in Physcomitrella, and single and double disruptants of these genes were generated. Using these disruptants, it was revealed that cryptochrome signals regulate many steps in moss development, including induction of side branching on protonema and gametophore induction and development. In addition, the disruption of cryptochromes altered auxin responses, including the expression of auxin-inducible genes. Cryptochrome disruptants were more sensitive to external auxin than wild type in a blue light-specific manner, suggesting that cryptochrome light signals repress auxin signals to control plant development. (+info)
Plant expansins are a complex multigene family with an ancient evolutionary origin.
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Expansins are a group of extracellular proteins that directly modify the mechanical properties of plant cell walls, leading to turgor-driven cell extension. Within the completely sequenced Arabidopsis genome, we identified 38 expansin sequences that fall into three discrete subfamilies. Based on phylogenetic analysis and shared intron patterns, we propose a new, systematic nomenclature of Arabidopsis expansins. Further phylogenetic analysis, including expansin sequences found here in monocots, pine (Pinus radiata, Pinus taeda), fern (Regnellidium diphyllum, Marsilea quadrifolia), and moss (Physcomitrella patens) indicate that the three plant expansin subfamilies arose and began diversifying very early in, if not before, colonization of land by plants. Closely related "expansin-like" sequences were also identified in the social amoeba, Dictyostelium discoidium, suggesting that these wall-modifying proteins have a very deep evolutionary origin. (+info)
Two early light-inducible protein (ELIP) cDNAs from the resurrection plant Tortula ruralis are differentially expressed in response to desiccation, rehydration, salinity, and high light.
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Tortula ruralis (Syntrichia ruralis) is a useful model system for the study of gene control in response to severe water deficit-stress. EST gene discovery efforts utilizing desiccated gametophytes have identified two cDNAs designated Elipa and Elipb with significant similarity to early light-inducible proteins (ELIPs). Elipa is 1006 bp in length, encoding a 212 amino acid deduced polypeptide (ELIPa) with a predicted molecular mass of 23.3 kDa and pI of 5.57. Elipb is 997 bp in length, encoding a 224 amino acid deduced polypeptide (ELIPb) with a predicted molecular mass of 24.4 kDa and pI of 9.27. Phylogenetic analysis demonstrated that ELIPa and ELIPb are reproducibly grouped with ELIP sequences derived from desiccation-tolerance tissues. RNA blot hybridization was used to analyse Elipa and Elipb mRNA abundance in response to a variety of stresses. Elipa steady-state transcript levels increased in response to slow desiccation, rapid desiccation/rehydration, salinity, ABA, and rehydration in high light. The Elipb transcript was only detectable in response to ABA or rehydration in high light. It is postulated that ELIPa and ELIPb are an adaptive response to stress-induced photodamage within the moss chloroplast, and play a key role in the protection and/or repair of the photosynthetic apparatus. (+info)
Two ancient classes of MIKC-type MADS-box genes are present in the moss Physcomitrella patens.
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Characterization of seven MADS-box genes, termed PPM1-PPM4 and PpMADS1-PpMADS3, from the moss model species Physcomitrella patens is reported. Phylogeny reconstructions and comparison of exon-intron structures revealed that the genes described here represent two different classes of homologous, yet distinct, MIKC-type MADS-box genes, termed MIKC(c)-type genes-"(c)" stands for "classic"-(PPM1, PPM2, PpMADS1) and MIKC(*)-type genes (PPM3, PPM4, PpMADS2, PpMADS3). The two gene classes deviate from each other in a characteristic way, especially in a sequence stretch termed intervening region. MIKC(c)-type genes are abundantly present in all land plants which have been investigated in this respect, and give rise to well-known gene types such as floral meristem and organ identity genes. In contrast, LAMB1 from the clubmoss Lycopodium annotinum was identified as the only other MIKC(*)-type gene published so far. Our findings strongly suggest that the most recent common ancestor of mosses and vascular plants contained at least one MIKC(c)-type and one MIKC(*)-type gene. Our studies thus reveal an ancient duplication of an MIKC-type gene that occurred before the separation of the lineages that led to extant mosses and vascular plants more than about 450 MYA. The identification of bona fide K-domains in both MIKC(*)-type and MIKC(c)-type proteins suggests that the K-domain is more ancient than is suggested by a recent alternative hypothesis. MIKC(*)-type genes may have escaped identification in ferns and seed plants so far. It seems more likely, however, that they represent a class of genes which has been lost in the lineage which led to extant ferns and seed plants. The high number of P. patens MADS-box genes and the presence of a K-box in the coding region and of some potential binding sites for MADS-domain proteins and other transcription factors in the putative promoter regions of these genes suggest that MADS-box genes in mosses are involved in complex gene regulatory networks similar to those in flowering plants. (+info)
Functional knockout of the adenosine 5'-phosphosulfate reductase gene in Physcomitrella patens revives an old route of sulfate assimilation.
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The reduction of adenosine 5'-phosphosulfate (APS) to sulfite catalyzed by adenosine 5'-phosphosulfate reductase is considered to be the key step of sulfate assimilation in higher plants. However, analogous to enteric bacteria, an alternative pathway of sulfate reduction via phosphoadenosine 5'-phosphosulfate (PAPS) was proposed. To date, the presence of the corresponding enzyme, PAPS reductase, could be neither confirmed nor excluded in plants. To find possible alternative routes of sulfate assimilation we disrupted the adenosine 5'-phosphosulfate reductase single copy gene in Physcomitrella patens by homologous recombination. This resulted in complete loss of the correct transcript and enzymatic activity. Surprisingly, the knockout plants grew on sulfate as the sole sulfur source, and the concentration of thiols in the knockouts did not differ from the wild type plants. However, when exposed to a sublethal concentration of cadmium, the knockouts were more sensitive than wild type plants. When fed [(35)S]sulfate, the knockouts incorporated (35)S in thiols; the flux through sulfate reduction was approximately 50% lower than in the wild type plants. PAPS reductase activity could not be measured with thioredoxin as reductant, but a cDNA and a gene coding for this enzyme were detected in P. patens. The moss Physcomitrella patens is thus the first plant species wherein PAPS reductase was confirmed on the molecular level and also the first organism wherein both APS- and PAPS-dependent sulfate assimilation co-exist. (+info)
Chloroplast ribosomal S14 protein transcript is edited to create a translation initiation codon in the moss Physcomitrella patens.
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The rps14 transcript is edited in the moss Physcomitrella patens chloroplast by a C-to-U transition, to create a translation initiation codon, AUG. The efficiency of RNA editing was low, with approximately 20% of rps14 transcripts edited. This suggests that the translation of rps14 mRNA is strictly regulated by RNA editing. This is the first report of RNA editing in P. patens and the creation of a translation initiation codon in rps14 mRNA in chloroplasts. (+info)