The expression of a peroxiredoxin antioxidant gene, AtPer1, in Arabidopsis thaliana is seed-specific and related to dormancy

We have isolated a gene, AtPer1, from the dicotyledon Arabidopsis thaliana, which shows similarity to the 1-cysteine (1-Cys) peroxiredoxin family of antioxidants. In higher plants, members of this group of antioxidants have previously only been isolated from monocotyledons. It has been suggested that seed peroxiredoxins protect tissues from reactive oxygen species during desiccation and early imbibition and/or are involved in the maintenance of/protection during dormancy. AtPer1 expression is restricted to seeds. Despite differences in seed development between monocots and dicots, AtPer1 shows an expression pattern during seed development and germination similar to the dormancy-related transcript Per1 in barley. In situ hybridization identifies AtPer1 as the first aleurone-expressed transcript characterized in developing Arabidopsis seeds. The transcript is also expressed in the embryo. AtPer1 expression in seeds is unaltered in an ABA-deficient mutant (aba-1) during seed development, while expression in seeds of an ABA-insensitive mutant (abi3-1) is reduced. The transcript is not induced in vegetative tissue in response to stress by ABA or drought. AtPer1 transcript levels are correlated to germination frequencies of wildtype seeds, but AtPer1 transcript abundance is not sufficient for expression of dormancy in non-dormant mutants. Hypotheses on peroxiredoxin function are discussed in view of the results presented here.

Characterization of cDNAs encoding small and large subunits of ADP-glucose pyrophosphorylases from watermelon (Citrullus vulgaris S.)

Three cDNA clones encoding ADP-glucose pyrophosphorylases were isolated from a full red fruit cDNA library of watermelon (Citrullus vulgaris S.). Sequence analyses indicated that one clone, wms1, corresponds to the small subunit, and two clones, wml1 and wml2 (a partial gene), are the large subunits of AGPase. The presumed AGPase proteins encoded by wms1, wml1, and wml2 have 526, 526, and 481 amino acids, respectively. The protein sequences have the conserved amino acids important for the substrate or regulator binding site, with some variation. Developmental changes in the amounts of wms1, wml1, and wml2 transcripts in fruits were measured by northern blot analysis. Their expression levels decreased from the small green to medium green stages, then increased in accordance with fruit ripening, which was different from those of tomato and oriental melon.

Molecular cloning and organ-specific expression of three isoforms of tomato ADP-glucose pyrophosphorylase gene

We isolated three cDNAs encoding different isoforms of ADP-glucose pyrophosphorylase (AGP) large submits from tomato plants. Three clones, designated AgpL1, AgpL2, and AgpL3 were 2019, 2105, and 1850bp, respectively. The clones had a long, uninterrupted open reading frame with a start codon at the 5' region and different copies of polyadenylation signal (AATAAA) at the 3' region, deriving 57-58kDa polypeptides. Sequence comparison and phylogenetic analysis revealed that the three isoforms represented different types of AGP large subunits, AgpL1 was strongly expressed in stems and weakly in roots. Accumulation of AgpL1 transcripts was found even in unpollinated ovaries and sustained at the early stages of fruit development. ApgL2 was expressed in roots and fruits. AgpL3 was exclusively expressed in leaves. The present study suggests that the three isoforms of tomato AGP large subunits are organ-specific in their expressions.

ADP-glucose pyrophosphorylase is localized to both the cytoplasm and plastids in developing pericarp of tomato fruit

The intracellular location of ADP-glucose pyrophosphorylase (AGP) in developing pericarp of tomato (Lycopersicon esculentum Mill) has been investigated by immunolocalization. With the use of a highly specific anti-tomato fruit AGP antibody, the enzyme was localized in cytoplasm as well as plastids at both the light and electron microscope levels. The immunogold particles in plastids were localized in the stroma and at the surface of the starch granule, whereas those in the cytoplasm occurred in cluster-like patterns. Contrary to the fruit, the labeling in tomato leaf cells occurred exclusively in the chloroplasts. These data demonstrate that AGP is localized to both the cytoplasm and plastids in developing pericarp cells of tomato.

Thioredoxins: structure and function in plant cells

Thioredoxins are ubiquitous small-molecular-weight proteins (typically 100-120 amino-acid residues) containing an extremely reactive disulphide bridge with a highly conserved sequence -Cys-Gly(Ala/Pro)-Pro-Cys-. In bacteria and animal cells, thioredoxins participate in multiple reactions which require reduction of disulphide bonds on selected target proteins/ enzymes. There is now ample biochemical evidence that thioredoxins exert very specific functions in plants, the best documented being the redox regulation of chloroplast enzymes. Another area in which thioredoxins are believed to play a prominent role is in reserve protein mobilization during the process of germination. It has been discovered that thioredoxins constitute a large multigene family in plants with different-subcellular localizations, a unique feature in living cells so far. Evolutionary studies based on these molecules will be discussed, as well as the available biochemical and genetic evidence related to their functions in plant cells. Eukaryotic photosynthetic plant cells are also unique in that they possess two different reducing systems, one extrachloroplastic dependent on NADPH as an electron donor, and the other one chloroplastic, dependent on photoreduced ferredoxin. This review will examine in detail the latest progresses in the area of thioredoxin structural biology in plants, this protein being an excellent model for this purpose. The structural features of the reducing enzymes ferredoxin thioredoxin reductase and NADPH thioredoxin reductase will also be described. The properties of the target enzymes known so far in plants will be detailed with special emphasis on the structural features which make them redox regulatory. Based on sequence analysis, evidence will be presented that redox regulation of enzymes of the biosynthetic pathways first appeared in cyanobacteria possibly as a way to cope with the oxidants produced by oxygenic photosynthesis. It became more elaborate in the chloroplasts of higher plants where a co-ordinated functioning of the chloroplastic and extra chloroplastic metabolisms is required. CONTENTS Summary 543 I. Introduction 544 II. Thioredoxins from photosynthetic organisms as a structural model 545 III. Physiological functions 552 IV. The thioredoxin reduction systems 556 V. Structural aspects of target enzymes 558 VI. Concluding remarks 563 Acknowledgements 564 References 564.

THE SYNTHESIS OF THE STARCH GRANULE

This review describes and discusses the implications of recent discoveries about how starch polymers are synthesized and organized to form a starch granule. Three issues are highlighted. 1. The role and importance of ADPglucose pyrophosphorylase in the generation of ADPglucose as the substrate for polymer synthesis. 2. The contributions of isoforms of starch-branching enzyme, starch synthase, and debranching enzyme to the synthesis and ordered packing of amylopectin molecules. 3. The requirements for and regulation of the synthesis of amylose.

Molecular cloning and expression of the large subunit of ADP-glucose pyrophosphorylase from barley (Hordeum vulgare) leaves

A cDNA clone, blpl14, corresponding to the large subunit of ADP-glucose pyrophosphorylase (AGPase), has been isolated from a cDNA library prepared from leaves of barley (Hordeum vulgare L.). An open reading frame encodes a protein of 503 aa, with a calculated molecular weight of 54815. The derived aa sequence contains a putative transit peptide sequence, required for targeting to plastids, and has a highly conserved positioning of critical Lys residues that are believed to be involved in effector binding. The derived aa sequence shows 97% identity with the corresponding protein from wheat, but only 36% identity with AGPase from E. coli. The blpl14 gene is expressed predominantly in leaves and to a lesser degree in seed endosperm, but not roots, of barley.

Excision of the maize transposable element Ac in periclinal chimeric leaves of 35S-Ac-rolC transgenic aspen-Populus

The transposable element Ac from maize, in combination with the phenotypic selectable marker rolC, was employed in transformation experiments of a hybrid aspen clone. A number of transgenic clones exhibited light-green sectors on green leaves. In vitro regeneration from leaves showing a high number of light-green spots resulted in R2 plants, which also showed light-green sectored leaves. However, only one out of 385 regenerated plants obtained showed green leaves. Both PCR and northern analysis indicated Ac excision and restoration of rolC expression. In Southern blot analysis of this green plant additional bands were observed as compared to the original R1 plant. The occurrence of these bands and a suggested Ac excision in the non-green L1-epidermal layer leading to periclinal chimerism of this plant is discussed.

New potential markers of in vitro tomato morphogenesis identified by mRNA differential display

The identification of plant genes involved in early phases of in vitro morphogenesis can not only contribute to our understanding of the processes underlying growth regulator-controlled determination, but also provide novel markers for evaluating the outcome of in vitro regeneration experiments. To search for such genes and to monitor changes in gene expression accompanying in vitro regeneration, we have adapted the mRNA differential display technique to the comparative analysis of a model system of tomato cotyledons that can be driven selectively toward either shoot or callus formation by means of previously determined growth regulator supplementations. Hormone-independent transcriptional modulation (mainly down-regulation) has been found to be the most common event, indicating that a non-specific reprogramming of gene expression quantitatively predominates during the early phases of in vitro culture. However, cDNA fragments representative of genes that are either down-regulated or induced in a programme-specific manner could also be identified, and two of them (G35, G36) were further characterized. One of these cDNA fragments, G35, corresponds to an mRNA that is down-regulated much earlier in callus- (day 2) than in shoot-determined explants (day 6). The other, G36, identifies an mRNA that is transiently expressed in shoot-determined explants only, well before any macroscopic signs of differentiation become apparent, and thus exhibits typical features of a morphogenetic marker.

A peroxiredoxin antioxidant is encoded by a dormancy-related gene, Per1, expressed during late development in the aleurone and embryo of barley grains

Antioxidants can remove damaging reactive oxygen species produced as by-products of desiccation and respiration during late embryogenesis, imbibition of dormant seeds and germination. We have expressed a protein, PER1, encoded by the Balem (barley aleurone and embryo) transcript previously called B15C, and show it to reduce oxidative damage in vitro. PER1 shares high similarity to a novel group of thiol-requiring antioxidants, named peroxiredoxins, and represents a subgroup with only one conserved cysteine residue (1-Cys). PER1 is the first antioxidant belonging to the 1-Cys subgroup shown to be functionally active, and the first peroxiredoxin of any kind to be functionally described in plants. The steady state level of the transcript, Per1, homologous to a dormancy-related transcript (pBS128) from bromegrass (Bromus secalinus), increases considerably in imbibed embryos from dormant barley (Hordeum vulgare L.) grains. Our investigations also indicate that Per1 transcript levels are dormancy-related in the aleurone layer of whole grains. In contrast to most seed-expressed antioxidants Per1 disappears in germinating embryos, and in the mature aleurone the transcript is down-regulated by the germinating embryo or by gibberellic acid (GA). Our data show that the barley seed peroxiredoxin is encoded by a single Per1 gene. Possible roles of the PER1 peroxiredoxin in barley grains during desiccation, dormancy and imbibition are discussed.

Isolation of molecular markers from the barley endosperm coenocyte and the surrounding nucellus cell layers

The cereal endosperm develops from a coenocyte to a cellular storage organ through formation of nucleo-cytoplasmic domains and cell wall deposition in the interzones between these domains. During its early stages, the endosperm develops in close contact with nucellus, the sporophytic tissue which gives rise to the megagametophyte. Owing to the positioning of the two tissues deeply within the ovary, neither cell types have been easily accessible for molecular studies. In this paper we report for the first time the cloning of molecular markers for the barley endosperm coenocyte and the nucellus. The novel END1 and NUC1 cDNAs were isolated by differential screening of a cDNA library from 5 DAP (days after pollination) ovaries using a positive probe from hand-dissected embryo sacs with adhering nucellus and testa cell layers, and a negative probe from pericarp. In situ and northern blot hybridization data show that END1 transcripts are asymmetrically distributed in the endosperm coenocyte limited to an area over the nucellar projection. In the cellular endosperm, END1 transcripts are present in modified aleurone cells and a few layers of ventral starchy endosperm cells. The second clone, NUC1, hybridizes to transcripts in the nucellus before fertilization and in autolyzing nucellus cells after fertilization. At later stages, after the disappearance of nucellus, NUC1 transcripts are present in the nucellar epidermis and in the lateral cells of the nucellar projection. This work provide tools for future elucidation of the genes specifying endosperm histogenesis.

Primary structure and expression of plant homologues of animal and fungal thioredoxin-dependent peroxide reductases and bacterial alkyl hydroperoxide reductases

Higher plants express genes encoding peroxiredoxins of the two-cysteine type. This is concluded from the isolation of cDNAs from spinach (Spinacia oleracea) and barley (Hordeum vulgare cv. Gerbel) which are homologous to animal, fungal, and bacterial two-cysteine peroxiredoxins. Northern blot analysis indicated the presence of at least one corresponding gene in all angiosperms analyzed suggesting that bas1 is a member of an ubiquitous gene family encoding a protein of fundamental importance in oxidative stress defense also in plants. In barley, expression increased upon application of methyl viologen but was not affected by ozone. mRNA levels increased during deetiolation in the light. Maximal abundance of bas1 transcripts was observed in young developing shoot segments where cell division and elongation take place. Expression was insignificant in roots. The amount of bas1 protein was high in the leaf blade, particularly in etiolated plants, and did not respond to oxidative stress. bas1 protein was not detected in roots. From our data, we suggest that bas1 is an antioxidant enzyme particularly important in the developing shoot and photosynthesizing leaf.

LIPID-TRANSFER PROTEINS IN PLANTS

Lipid-transfer proteins (LTP) are basic, 9-kDa proteins present in high amounts (as much as 4% of the total soluble proteinss) in higher plants. LTPs can enhance the in vitro transfer of phospholipids between membranes and can bind acyl chains. On the basis of these properties, LTPs were thought to participate in membrane biogenesis and regulation of the intracellular fatty acid pools. However, the isolation of several cDNAs and genes revealed the presence of a signal peptide indicating that LTPs could enter the secretory pathway. They were found to be secreted and located in the cell wall. Thus, novel roles were suggested for plant LTPs: participation in cutin formation, embryogenesis, defense reactions against phytopathogens, symbiosis, and the adaptation of plants to various environmental conditions. The validity of these suggestions needs to be determined, in the hope that they will elucidate the role of this puzzling family of plant proteins.

Two new oleosin isoforms with altered expression patterns in seeds of the Arabidopsis mutant fus3

Oleosins are proteins associated with lipid bodies mainly synthesised during seed development. Using a subtractive hybridisation approach two new members of the oleosin gene family of Arabidopsis thaliana have been isolated. The quantitative and temporal expression patterns of both genes are found to be affected in the fus3 mutant defective in late embryogenesis. This pattern is interpreted as a molecular marker for a mutant specific developmental change from a seed maturation to a germination pathway.

Isolation of a root-specific cDNA encoding a ns-LTP-like protein from the roots of bean (Phaseolus vulgaris L.) seedlings

A root-specific cDNA clone, PVR3, was isolated from a bean (Phaseolus vulgaris L.) root cDNA library by a differential screening procedure. The nucleotide sequence of PVR3 contains an open reading frame coding for an 11.14 kDa polypeptide of 102 amino acid residues; the first 25 amino acids correspond to the sequence characteristic of a signal peptide. Comparison of the deduced PVR3 polypeptide sequence with the polypeptide sequences of previously cloned genes indicates that PVR3 may encode a ns-LTP-like protein. Molecular modelling of the PVR3 protein predicts that it has a three-dimensional structure that is similar to the three-dimensional model determined from the maize ns-LTP. The PVR3 mRNA accumulated mainly in the roots of young seedlings. It can be detected at low levels in flowers, but it is not detected in other organs. Genomic Southern blot analysis indicates that the genomic DNA corresponding to PVR3 cDNA is encoded by a single gene or small gene family in the bean genome.

A single gene encodes two different transcripts for the ADP-glucose pyrophosphorylase small subunit from barley (Hordeum vulgare)

ADP-glucose pyrophosphorylase (AGPase), a heterotetrameric enzyme composed of two small and two large subunits, catalyses the first committed step of starch synthesis in plant tissues. In an attempt to learn more about the organization and expression of the small-subunit gene of AGPase, we have studied the small-subunit transcripts as well as the structure of the gene encoding these transcripts in barley (Hordeum vulgare L. cv. Bomi). Two different transcripts (bepsF1 and blps14) were identified: bepF1 was abundantly expressed in the starchy endosperm but not in leaves, whereas blps14 was isolated from leaves but was also found to be present at a moderate level in the starchy endosperm. The sequences for the two transcripts are identical over approx. 90% of the length, with differences being confined solely to their 5' ends. In blps14, the unique 5' end is 259 nt long and encodes a putative plastid transit peptide sequence. For the 178-nt 5' end of bepsF1, on the other hand, no transit peptide sequence could be recognized. A lambda clone that hybridized to the AGPase transcripts was isolated from a barley genomic library and characterized. The restriction map has suggested a complex organization of the gene, with alternative exons encoding the different 5' ends of the two transcripts followed by nine exons coding for the common part of the transcripts. The sequence of a portion of the genomic clone, covering the alternative 5'-end exons as well as upstream regions, has verified that both transcripts are encoded by the gene. The results suggest that the small-subunit gene of barley AGPase transcribes two different mRNAs by a mechanism classified as alternative splicing.

A potential anti-oxidant protein in a ferrous iron-oxidizing Sulfolobus species

The production of a 25 kDa protein was greatly increased when a sulfur- and ferrous iron-oxidizing species of Sulfolobus was switched from growth on tetrathionate to growth on ferrous iron. The gene encoding the protein was cloned and sequenced. The predicted amino sequence showed significant similarity to those of the alkyl hydroperoxide reductase/thiol specific anti-oxidant family of proteins that appear to be involved in responses to certain types of oxidative stress.

Evolution of the Group 1 late embryogenesis abundant (Lea) genes: analysis of the Lea B19 gene family in barley

The highly conserved Group 1 late embryogenesis abundant (Lea) genes are present in the genome of most plants as a gene family. Family members are conserved along the entire coding region, especially within the extremely hydrophilic internal 20 amino acid motif, which may be repeated. Cloning of Lea Group 1 genes from barley resulted in the characterization of four family members named B19.1, B19.1b, B19.3 and B19.4 after the presence of this motif 1, 1, 3 and 4 times in each gene, respectively. We present here the results of comparative and evolutionary analyses of the barley Group 1 Lea gene family (B19). The most important findings resulting from this work are (1) the tandem clustering of B19.3 and B19.4, (2) the spatial conservation of putative regulatory elements between the four B19 gene promoters, (3) the determination of the relative 'age' of the gene family members and (4) the 'chimeric' nature of B19.3 and B19.4, reflecting a cross-over or gene-conversion event in their common ancestor. We also show evidence for the presence of one or two additional expressed B19 genes in the barley genome. Based on our results, we present a model for the evolution of the family in barley, including the 20 amino acid motif. Comparisons of the relatedness between the barley family and all other known Group 1 Lea genes using maximum parsimony (PAUP) analysis provide evidence for the time of divergence between the barley genes containing the internal motif as a single copy and as a repeat. The PAUP analyses also provide evidence for independent duplications of Group 1 genes containing the internal motif as a repeat in both monocots and dicots.

The transcripts encoding two oleosin isoforms are both present in the aleurone and in the embryo of barley (Hordeum vulgare L.) seeds

Two transcripts (Ole-1 and Ole-2) encoding two oleosin isoforms homologous to the 18 and 16 kDa oleosins of maize, respectively, have been isolated from developing barley embryos and aleurone layers where lipid bodies are highly abundant organelles. For each of the isoforms the aleurone and embryo transcripts are identical, indicating that the same genes are expressed in both tissues. The temporal accumulation of the two transcripts during seed development is similar. At a low frequency, lipid bodies are found also in starchy endosperm cells of barley. Accordingly, a low transcript level is observed for both oleosins during starchy endosperm development.

Molecular cloning and characterization of novel isoforms of potato ADP-glucose pyrophosphorylase

ADP-glucose pyrophosphorylase (AGPase) is one of the major enzymes involved in starch biosynthesis in higher plants. We report here the molecular cloning of two cDNAs encoding so far uncharacterized isoforms (AGP S2 and AGP S3) of the potato enzyme. Sequence analysis shows that the two polypeptides are more homologous to previously identified large subunit polypeptides from potato and other plant species than to small subunit isoforms. This observation suggest that AGP S2 and AGP S3 represent novel large subunit polypeptides. agpS2 is expressed in several tissues of the potato plant, including leaves and tubers. Expression was stronger in sink leaves than in source leaves, indicating developmental regulation. In leaves, agpS2 expression was induced 2- to 3-fold by exogenous sucrose; therefore, agpS2 represents a new sucrose-responsive gene of starch metabolism. Expression of agpS3 was restricted to tubers: no agpS3 expression could be seen in leaves of different developmental stages, or when leaves were incubated in sucrose. Therefore, agpS3 represents the only AGPase gene so far characterized from potato, which is not expressed in leaves. Conversely, all four AGPase isoforms known from potato are expressed in tubers.

Isolation and expression analysis of cDNA clones encoding a small and a large subunit of ADP-glucose pyrophosphorylase from sugar beet

The cDNA cloning of a small and a large subunit of ADP-glucose pyrophosphorylase (AGPase) from sugar beet is reported. The deduced amino acid sequences are highly homologous to previously identified AGPase polypeptides from other plant species. Both subunits are encoded by low copy genes. When RNA gel blot experiments were performed, strongest expression was detected in sink and source leaves of greenhouse-grown sugar beet plants. A lower expression was found in other tissues tested, i.e. in the hypocotyl, the tap root and roots. In these tissues, slightly higher transcript levels were found for the small subunit gene than for the large subunit gene.

Genetic control of androgenetic response in Lolium perenne L

In a study of androgenesis in 90 Norwegian genotypes of perennial ryegrass (Lolium perenne L.), heritabilities ranged from h b (2) =0.46 to 0.80. Very high or completely positive genotypic correlations were found between most characters of androgenetic response (e.g. embryo-like structures per 100 anthers, plants per 100 embryo-like structures, albino plants per 100 anthers, green plants per 100 anthers). Three genotypes, 2 Norwegian (7-5 and 9-5) and 1 Danish (245), which had significantly different androgenetic responses were selected to study the genetic control of the processes. Genotypes 7-5 and 9-5 were highly embryogenie, 7-5 and 245 were relatively high producers of green plants, while 9-5 was unable to produce green plants. The six possible reciprocal crosses between these three genotypes were made, and 10 or 11 F1 plants from each cross were used for anther culture experiments. The cross 7-5 x 245 showed average superiority over both parents for total plant regeneration and green plant production, results not previously reported. The phenotypic correlations estimated among progenies from the crosses ranged from r=-0.99(***) to 0.81(***). These considerable changes, relative to the results of the screening experiment, are most likely the result of changed allele frequencies caused by the strong selection of parents in these crosses, and a relatively simple genetical control. This is also inferred from the large transgressive segregation observed.

Cloning and characterization of five cDNAs for genes differentially expressed during fruit development of kiwifruit (Actinidia deliciosa var. deliciosa)

Five cDNAs for genes differentially expressed during fruit development of kiwifruit (Actinidia deliciosa var. deliciosa cv. Hayward) were isolated from a library made from young fruit, 8-10 days after anthesis. One gene (pKIWI503) has low levels of expression in young fruit but is induced late in fruit development and during fruit ripening, and has some homology to plant metallothionein-like proteins. The other four genes are highly expressed in young fruit with reduced expression in the later stages of fruit development. pKIWI504 has strong homology to plant metallothionein-like proteins and pKIWI505 exhibits homology to the beta-subunit of the mitochondrial ATP synthase gene. The two other genes (pKIWI501 and 502) encode proteins with no significant homology to other known sequences.

A fatty-acid-binding protein from wheat kernels

A protein of about 7 kDa (W-FABP) has been isolated from mature wheat kernels by H2O extraction and gel filtration of the extract, followed by two steps of high-performance liquid chromatography. The N-terminal amino acid-sequence has been determined up to the 28th residue and found to be identical (except for positions 4 and 5) to that deduced from a barley cDNA (EMBL X15257), which had been improperly classified as a non-specific lipid transfer protein (LTP2). Similarly with LTPs, W-FABP does bind fatty acids, but in contrast, it is not significantly homologous to LTPs, it is not recognized by LTP antibodies, it has a more acidic isoelectric point (pH < 6.8 vs. pH > 9.6), and it does not show antibiotic properties.

Chloroplast targeting of spectinomycin adenyltransferase provides a cell-autonomous marker for monitoring transposon excision in tomato and tobacco

Antibiotic resistance genes can act as either cell autonomous or non-cell autonomous genetic markers with which to monitor the excision of plant transposons. To convert spectinomycin resistance from a non-cell autonomous resistance to cell autonomous resistance, a transit peptide for chloroplast localization from a petunia ribulose bisphosphate carboxylase (rbcS) gene was fused in-frame to the aadA gene, which confers spectinomycin and streptomycin resistance. Constructs were generated in which the expression of this chimeric gene was prevented by the presence, in the 5' untranslated leader, of the maize transposons Activator (Ac) or Dissociation (Ds). When progeny of tobacco or tomato plants transformed with these constructs were germinated on spectinomycin-containing medium, germinally revertant and somatically variegated individuals could be distinguished.

Characterization of a rice gene coding for a lipid transfer protein

The cloning and sequence analysis of a gene that encodes a lipid transfer protein (LTP) from rice is reported. A genomic DNA library from Oryza sativa was screened using a cDNA encoding a maize LTP. One genomic clone containing the gene (Ltp) was partially sequenced and analyzed. The open reading frame is interrupted by an 89-bp intron. From the results of Southern hybridizations, Ltp appears to be a member of a small multigenic family. Transcripts of the corresponding gene were detected in several tissues including coleoptile, leaf, endosperm, scutellum and root. The transcription start point was determined by primer extension. The deduced amino-acid sequence of the Ltp product is shown to be homologous to LTPs from other crops.

Analysis of the chromosomal distribution of transposon-carrying T-DNAs in tomato using the inverse polymerase chain reaction

We are developing a system for isolating tomato genes by transposon mutagenesis. In maize and tobacco, the transposon Activator (Ac) transposes preferentially to genetically linked sites. To identify transposons linked to various target genes, we have determined the RFLP map locations of Ac- and Dissociation (Ds)-carrying T-DNAs in a number of transformants. T-DNA flanking sequences were isolated using the inverse polymerase chain reaction (IPCR) and located on the RFLP map of tomato. The authenticity of IPCR reaction products was tested by several criteria including nested primer amplification, DNA sequence analysis and PCR amplification of the corresponding insertion target sequences. We report the RFLP map locations of 37 transposon-carrying T-DNAs. We also report the map locations of nine transposed Ds elements. T-DNAs were identified on all chromosomes except chromosome 6. Our data revealed no apparent chromosomal preference for T-DNA integration events. Lines carrying transposons at known map locations have been established which should prove a useful resource for isolating tomato genes by transposon mutagenesis.

Mapping of the ADP-glucose pyrophosphorylase genes in barley

cDNA probes encoding the barley endosperm ADP-glucose pyrophosphorylase (AGP) small subunit (bepsF2), large subunit (bepl10), and leaf AGP large subunit (blpl) were hybridized with barley genomic DNA blots to determine copy number and polymorphism. Probes showing polymorphism were mapped on a barley RFLP map. Probes that were not polymorphic were assigned to chromosome arms using wheat-barley telosomic addition lines. The data suggested the presence of a single-copy gene corresponding to each of the cDNA probes. In addition to the major bands, several weaker cross-hybridizing bands indicated the presence of other, related sequences. The weaker bands were specific to each probe and were not due to cross-hybridization with the other probes examined here. The endosperm AGP small subunit (bepsF2) majorband locus was associated with chromosome 1P and designated Aga1. The endosperm AGP large subunit (bepl10) major-band locus was mapped to chromosome 5M and designated Aga7. The endosperm AGP large-subunit minor bands were not mapped. The leaf AGP large-subunit major band was associated with chromosome 7M and designated Aga5. One of the leaf AGP large-subunit minor bands was mapped to chromosome 5P and designated Aga6. A clone for the wheat endosperm AGP large-subunit (pAga7) hybridized to the same barley genomic DNA bands as the corresponding barley probe indicating a high degree of identity between the two probes.

Molecular characterization of multiple cDNA clones for ADP-glucose pyrophosphorylase from Arabidopsis thaliana

PCR amplification of cDNA prepared from poly(A)+ RNA from aerial parts of Arabidopsis thaliana, using degenerate nucleotide primers based on conserved regions between the large and small subunits of ADP-glucose pyrophosphorylase (AGP), yielded four different cDNAs of ca. 550 nucleotides each. Based on derived amino acid sequences, the identities between the clones varied from 49 to 69%. Sequence comparison to previously published cDNAs for AGP from various species and tissues has revealed that three of the amplified cDNAs (ApL1, ApL2 and ApL3) correspond to the large subunit of AGP, and one cDNA (ApS) encodes the small subunit of AGP. Both ApL1 and ApS were subsequently found to be present in a cDNA library made from Arabidopsis leaves. All four PCR products are encoded by single genes, as found by genomic Southern analysis.

Constitutive or light-regulated expression of the rolC gene in transgenic potato plants has different effects on yield attributes and tuber carbohydrate composition

Tetraploid potato clones, transgenic for the rolC gene of Agrobacterium rhizogenes under control of the light-inducible ribulose bisphosphate carboxylase small subunit promoter (rbcS-rolC), were compared, with respect to yield attributes and tuber carbohydrates, with transformed and untransformed controls and with 35S-rolC transgenic potato plants. In rbcS-rolC plants, the expression of the rolC gene was located mainly in leaves, while in 35S-rolC plant transcripts were detected as well in shoots and roots. Phenotypically, rbcS-rolC transgenic plants were found to be slightly reduced in plant size with a few more tillers than control plants. Photosynthetic rate and chlorophyll content were significantly lower in all rolC transgenic plants irrespective of the type of construct used. Tuber yield was not significantly different between controls and rbcS-rolC transgenic plants, but was reduced in the 35S-rolC transformants. Sucrose level was unchanged in all rolC clones investigated, whereas fructose content was significantly enhanced in 35S-rolC transformants, but not in the plants expressing the rolC gene in aerial plant parts only. In both types of rolC transgenic plants, glucose content was lower than in controls, resulting in a significant reduction of reducing sugar in tubers. The results suggest a hormonal influence on the carbohydrate composition of potato tubers.

Plant metallothioneins

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Hormonal Characterization of Transgenic Tobacco Plants Expressing the rolC Gene of Agrobacterium rhizogenes TL-DNA

Transgenic tobacco (Nicotiana tabacum L. cv Wisconsin 38) plants expressing the Agrobacterium rhizogenes rolC gene under the control of the cauliflower mosaic virus 35S RNA promoter were constructed. These plants displayed several morphological alterations reminiscent of changes in indole-3-acetic acid (IAA), cytokinin, and gibberellin (GA) content. However, investigations showed that neither the IAA pool size nor its rate of turnover were altered significantly in the rolC plants. The biggest difference between rolC and wild-type plants was in the concentrations of the cytokinin, isopentenyladenosine (iPA) and the gibberellin GA19. Radio-immunoassay and liquid chromatography-mass spectrometry measurements revealed a drastic reduction in rolC plants of iPA as well as in several other cytokinins tested, suggesting a possible reduction in the synthesis rate of cytokinins. Furthermore, gas chromatography-mass spectrometry quantifications of GA19 showed a 5- to 6-fold increase in rolC plants compared with wild-type plants, indicating a reduced activity of the GA19 oxidase, a proposed regulatory step in the gibberellin biosynthesis. Thus, we conclude that RolC activity in transgenic plants leads to major alterations in the metabolism of cytokinins and gibberellins.

Restoration of fertility by antisense RNA in genetically engineered male sterile tobacco plants

Transgenic tobacco plants (Nicotiana tabacum L.) expressing the rolC gene of Agrobacterium rhizogenes under the transcriptional control of the 35S RNA promoter are male sterile. When these plants are genetically crossed with others containing the rolC gene linked in antisense orientation to the 35S RNA promoter, hybrid progeny display restoration of male fertility. Moreover, hybrid progeny are revertant for other features of the rolC phenotype, such as restoration of plant height, leaf pigment content and female fertility. The level of restoration of the characteristics of untransformed tobacco appeared to be independent of the steady-state level of antisense RNA. Addition of six transcriptional enhancer sequences upstream of the 35S transcriptional start region in the antisense construct led to a higher steady-state level of antisense RNA than that produced using a promoter linked to a single enhancer sequence. However no significant difference was observed in the level of attenuation of the rolC phenotype in the progeny of crosses with either one or six transcriptional enhancers linked to the antisense rolC gene. Antisense constructs comprising only 189 bp of the rolC 5' coding region appeared less efficient in attenuating the rolC phenotype than those including the whole rolC coding region as well as its 3' untranslated region. Furthermore, results from experiments on light-controlled rolC gene expression indicate that microsporogenesis is sensitive to rolC gene action during the early stages of flower development.

Transgenic tobacco plants regenerated from leaf disks can be periclinal chimeras

Amongst rolC transgenic tobacco plants regenerated from leaf disks 6.5% are periclinal chimeras, i.e. plants with genetically different cell populations in different cell layers. The expression of the rolC gene of Agrobacterium rhizogenes causes a reduction in pigment content in leaves. The chimeric composition of the regenerated plants becomes thus apparent as light green leaf tissue in the transgenic region, tissue flanked by dark green wild-type sectors. Southern and northern blot analysis confirmed the chimeric nature of such plants. Investigation of selfed progeny of chimeric plants on selective media indicates that layer invasion in reproductive tissues can occur in tobacco early during the formation of the flower buds. The results show (1) that tobacco plants regenerated from leaf disks and grown on selective media have not necessarily the same clonal origin and (2) that they can give rise to non-transgenic offspring. The chimeric plants provide insight on the effect of rolC gene expression on microsporogenesis.

Promotion of flowering and morphological alterations in Atropa belladonna transformed with a CaMV 35S-rolC chimeric gene of the Ri plasmid

Kanamycin-resistant plants of belladonna (Atropa belladonna) were obtained after Agrobacterium mediated transformation. When a rolC gene, which is one of the loci located on Ri plasmid of Agrobacterium rhizogenes, was co-introduced with a kanamycin resistant (NPT II) gene under control of a cauliflower mosaic virus 35S promoter, the rolC gene was expressed strongly in leaves, flowers, stems and roots. The transformed plants exhibited dramatic promotion of flowering, reduced apical dominance, pale and lanceolated leaves and smaller flowers. On the other hand, when native rolC gene was co-introduced with NPT II, the transgenic plants obtained did not exhibit the altered phenotypes observed in 35S-rolC transformants, and the expression level of the rolC gene was much lower than in 35S-rolC transformants. These results suggest that the morphological changes in transgenic Atropa belladonna were related to the degree of expression of the rolC gene.

PCR amplification and sequences of cDNA clones for the small and large subunits of ADP-glucose pyrophosphorylase from barley tissues

Several cDNAs encoding the small and large subunit of ADP-glucose pyrophosphorylase (AGP) were isolated from total RNA of the starchy endosperm, roots and leaves of barley by polymerase chain reaction (PCR). Sets of degenerate oligonucleotide primers, based on previously published conserved amino acid sequences of plant AGP, were used for synthesis and amplification of the cDNAs. For either the endosperm, roots and leaves, the restriction analysis of PCR products (ca. 550 nucleotides each) has revealed heterogeneity, suggesting presence of three transcripts for AGP in the endosperm and roots, and up to two AGP transcripts in the leaf tissue. Based on the derived amino acid sequences, two clones from the endosperm, beps and bepl, were identified as coding for the small and large subunit of AGP, respectively, while a leaf transcript (blpl) encoded the putative large subunit of AGP. There was about 50% identity between the endosperm clones, and both of them were about 60% identical to the leaf cDNA. Northern blot analysis has indicated that beps and bepl are expressed in both the endosperm and roots, while blpl is detectable only in leaves. Application of the PCR technique in studies on gene structure and gene expression of plant AGP is discussed.

Late embryogenesis-abundant genes encoding proteins with different numbers of hydrophilic repeats are regulated differentially by abscisic acid and osmotic stress

The late embryogenesis-abundant (Lea) genes, which are suggested to act as desiccation protectants during seed desiccation and in water-stressed seedlings, can be induced by abscisic acid (ABA) and various kinds of water-related stress. Using cotton Lea cDNAs as probes it was found that several of the Lea genes are conserved at the mRNA level in dicots and monocots. By screening a barley cDNA library with a cotton Lea D19 cDNA a family of three members was isolated. The putative B19 proteins have strong similarities to the Em protein in wheat and to LEA proteins from several dicots. However, the middle part of the B19 proteins consists of a 20-amino acid motif repeated three and four times in B19.3 and B19.4, respectively, but only once in B19.1. The gene products are strongly hydrophilic, the internal 20-amino acid motif being the most hydrophilic part. This motif is found once in cotton Lea D19 but is repeated twice in cotton Lea D132, indicating that the repeats are universal among monocot and dicot B19-like genes. The B19 genes are regulated similarly during embryo development, but to very different levels. In contrast, they are differentially regulated by ABA and various types of osmotic stress. In immature embryos all three genes are responsive to ABA and mannitol. However, B19.1 is also responsive to salt. Cold stress does not induce B19 mRNAs; only a stabilization of the transcript levels is seen. These results suggest that the responses to salt stress and exogenous ABA operate through different pathways.

Cell lineage in plant development

Lineage analyses in several plant species demonstrate that meristematic cells proliferate in a predictable manner to form the differentiated tissues of the mature shoot system. These studies also demonstrate, however, that the fates of meristematic cells are not absolutely dependent on their lineage. This variability indicates that interactions between cells must play a role in morphogenesis.

The plant oncogene rolC is responsible for the release of cytokinins from glucoside conjugates

The rolC gene of Agrobacterium rhizogenes, which drastically affects growth and development of transgenic plants, codes for a cytokinin-beta-glucosidase. Indeed, rolC protein expressed in Escherichia coli as a fusion protein hydrolyses cytokinin glucosides, thus liberating free cytokinins. Furthermore, beta-glucosidase activity present in E. coli extracts expressing the rolC protein was inhibited by affinity-purified antibodies specific for the rolC protein. Finally, rolC proteins expressed in transgenic plants were shown to be responsible for cytokinin-beta-glucosidase activity. Morphological and phytohormonal analysis, performed on transgenic plants that are somatic mosaics for the expression of the rolC gene, extend and confirm our interpretation that the developmental, physiological and morphological alterations caused by rolC expression in transgenic plants are primarily due to a modification of the cytokinin balance. These observations shed new light on the control of growth and differentiation in plants by growth factors.

Cytosolic localization in transgenic plants of the rolC peptide from Agrobacterium rhizogenes

The rolC gene of Agrobacterium rhizogenes codes for a peptide with an apparent molecular weight of approximately 20 kDa. Immunolocalization of the rolC peptide, in leaves of transgenic plants which are genetic mosaics for the expression of the rolC gene, is restricted to the phenotypically altered sectors. Subcellular fractionation of homogenates from 35S-rolC transgenic leaves shows the cytosolic localization of the rolC peptide.

Cell lineage in plant development

Lineage analyses in several plant species demonstrate that meristematic cells proliferate in a predictable manner to form the differentiated tissues of the mature shoot system. These studies also demonstrate, however, that the fates of meristematic cells are not absolutely dependent on their lineage. This variability indicates that interactions between cells must play a role in morphogenesis.