Changes in legumin messenger RNAs throughout seed development in Pisum sativum L

Characterization of a new rice glutelin gene GluD-1 expressed in the starchy endosperm

A new glutelin gene, designated GluD-1, has been discovered by comparing the seed storage proteins from 48 japonica and indica rice cultivars on SDS-PAGE gels. Evidence that GluD-1 is a member of the glutelin family was provided by Western blots using anti-glutelin antiserum and by mapping the gene to the chromosomal glutelin gene cluster. The limited GluD-1 size polymorphism among the rice varieties is due to amino acid substitutions rather than to post-transcriptional modification. GluD-1 is maximally expressed in the starchy endosperm starting at 5 d after flowering (DAF) and increasing through 30 DAF, a major difference from the other glutelins which are primarily expressed in the subaleurone from 10-16 DAF. Only about 0.2 kb of the GluD-1 promoter was sufficient to confer inner starchy endosperm-specific expression. The 0.2 kb truncated GluD-1 promoter contains a bifactorial endosperm box consisting of a truncated GCN4 motif (TGA(G/C)TCA) and AAAG Prolamin box (P box), and ACGT and AACA motifs as cis-regulatory elements. Gel retardation assays and trans-activation experiments indicated that the truncated GCN4 and P box are specifically recognized by RISBZ1 b-ZIP and RPBF Dof activators in vitro, respectively, and are synergistically transactivated, indicating that combinatorial interactions of these motifs are involved in essential endosperm-specific regulation. Furthermore, deviation from the cognate GCN4 motif alters tissue-specific expression in the inner starchy endosperm to include other endosperm tissues.

Temporal and spatial activity of a promoter from a pea enzyme inhibitor gene and its exploitation for seed quality improvement

The promoter from one of the two seed-expressed genes encoding trypsin/chymotrypsin inhibitors (TI) has been isolated and characterised in transgenic pea lines, following its re-introduction by Agrobacterium-mediated transformation, as a TI promoter-beta-glucuronidase (GUS) gene fusion. The promoter from this gene (TI1) directed expression of GUS enzyme at late stages of embryogenesis, comparable to those determined for activity of the homologous native TI genes. GUS expression was detected in roots of plants subjected to drought stress conditions, indicating that the TI1 gene, normally seed-specific in its expression, can be induced under these conditions. A second gene construct utilised the TI1 gene promoter to direct expression of an antisense TI gene. Seed TI activities in some lines transformed with this construct were reduced significantly. A limitation of the pea transformation methodology for antisense manipulations, in particular, is the observed frequency of non-transmission of transgenes from primary transformants (up to 80%).

Cloning of a cDNA encoded by a member of the Arabidopsis thaliana ATP sulfurylase multigene family. Expression studies in yeast and in relation to plant sulfur nutrition

An Arabidopsis thaliana ATP sulfurylase cDNA (ASA1), encoding a putative chloroplastic isoform, has been cloned by functional complementation of a Saccharomyces cerevisiae (met3) ATP sulfurylase mutant which also has a poor sulfate transport capacity. Homologous complementation of the yeast mutant with the ATP sulfurylase gene restores both ATP sulfurylase function and sulfate transport. Heterologous complementation restores only ATP sulfurylase function as demonstrated by low [35S]sulfate influx measurements and selenate resistance. A structural relationship between ATP sulfurylase and sulfate membrane transporters in yeast is proposed. The sequence of ASA1 is homologous to deduced plant and animal ATP sulfurylase sequences. Analyses indicate a potential tyrosine phosphorylation site which is unique to higher eukaryote sequences. ASA1 is specified by a single copy gene that is part of a multigene family in A. thaliana. At least two ASA1 copies are found in Brassica napus plants. ASA1 transcripts were found in all organs examined, with the highest transcript abundance and ATP sulfurylase activity in leaves or cotyledons. Absence of sulfate from culture media transiently increased B. napus transcript abundance, indicating that initially, the response to sulfate deprivation is transcriptionally regulated.

Multiple isoforms of Pisum trypsin inhibitors result from modification of two primary gene products

Characterization of Pisum (pea) seed trypsin inhibitors (TI) and their corresponding cDNAs indicates that the pea TI gene family contains two genes. The existence of multiple TI isoforms can be attributed to post-translational modifications of primary gene products. Post-translational processing at the C-terminus during the desiccation stage of seed development results in the appearance of TI isoforms with increased affinity for the target enzyme, trypsin.

Gene activity during germination of spores of the fern, Onoclea sensibilis. Cell-free translation analysis of mRNA of spores and the effect of alpha-amanitin on spore germination

Poly(A)-RNA fractions of dormant, dark-imbibed (non-germinating) and photoinduced (germinating) spores of Onoclea sensibilis were poor templates in the rabbit reticulocyte lysate protein synthesizing system, but the translational efficiency of poly(A)+RNA was considerably higher than that of unfractionated RNA. Poly(A)+RNA isolated from photoinduced spores had a consistently higher translational efficiency than poly(A)+RNA from dark-imbibed spores. Analysis of the translation products by one-dimensional polyacrylamide gel electrophoresis showed no qualitative differences in the mRNA populations of dormant, dark-imbibed, and photoinduced spores. However, poly(A)+RNA from dark-imbibed spores appeared to encode in vitro fewer detectable polypeptides at a reduced intensity than photoinduced spores. A DNA clone encoding the large subunit of maize ribulose bisphosphate carboxylase hybridized at strong to moderate intensity to RNA isolated from dark-imbibed spores, indicating the absence of mRNA degradation. Although alpha-amanitin did not inhibit the germination of spores, the drug prevented the elongation of the rhizoid and protonemal initial with a concomitant effect on the synthesis of poly(A)+RNA. These results are consistent with the view that some form of translational control involving stored mRNA operates during dark-imbibition and photoinduced germination of spores.

Genomic DNA sequences of two new genes for new storage protein glutelin in rice

A new cDNA and two genomic genes encoding the rice storage protein glutelin were isolated and sequenced. The nucleotide sequence of one gene (GluA-3) was completely identical with that of the new cDNA identified here, and the other (GluA-4) was a pseudogene. These glutelin genes were closely related to each other, and belonged to the subfamily A containing the type I (GluA-1) and II (GluA-2) glutelin genes. The Northern blot analysis, using synthetic oligonucleotide specific to the GluA-3 gene as a probe, showed that this gene was expressed earlier than other glutelin genes during seed maturation.

The effect of different alleles at the r locus on the synthesis of seed storage proteins in Pisum sativum

Rocket immunoelectrophoresis was used to measure the accumulation of storage proteins in developing cotyledons of two Pisum sativum (pea) genotypes, that were close to isogenic except for the nature of the allele at the r locus. There was a marked decrease in legumin accumulation in the rr (wrinkled-seeded) genotype compared to the RR (round-seeded) genotype. The accumulation of vicilin did not differ greatly between the two genotypes. Pulse-labelling studies indicated that the differences in rates of accumulation of legumin between the rr and RR genotypes were a consequence of differences in rates of protein synthesis. Measurements of relative amounts of specific mRNAs, using cDNA clones as probes, showed lower amounts of legumin mRNA in developing cotyledons of the rr, compared to the RR, genotype. Both vicilin mRNAs and convicilin mRNA, the latter of which shows a similar temporal pattern of expression to those of the major legumin species, are relatively unaffected by the nature of the allele at the r locus. Nuclear run-on transcription experiments indicated no differences in the rate of synthesis of legumin transcripts in the rr and RR near-isolines. The consequences of homozygosity for the r allele on storage protein mRNA levels in vitro may be mimicked by manipulating the sucrose concentration of the culture medium.

The gene for trypsin inhibitor CMe is regulated in trans by the lys 3a locus in the endosperm of barley (Hordeum vulgare L.)

A cDNA encoding trypsin inhibitor CMe from barley endosperm has been cloned and characterized. The longest open reading frame of the cloned cDNA codes for a typical signal peptide of 24 residues followed by a sequence which is identical to the known amino acid sequence of the inhibitor, except for an Ile/Leu substitution at position 59. Southern blot analysis of wheat-barley addition lines has shown that chromosome 3H of barley carries the gene for CMe. This protein is present at less than 2%-3% of the wild-type amount in the mature endosperm of the mutant Risø 1508 with respect to Bomi barley, from which it has been derived, and the corresponding steady state levels of the CMe mRNA are about 1%. One or two copies of the CMe gene (synonym Itc1) per haploid genome have been estimated both in the wild type and in the mutant, and DNA restriction patterns are identical in both stocks, so neither a change in copy number nor a major rearrangement of the structural gene account for the markedly decreased expression. The mutation at the lys 3a locus in Risø 1508 has been previously mapped in chromosome 7 (synonym 5H). A single dose of the wild-type allele at this locus (Lys 3a) restores the expression of gene CMe (allele CMe-1) in chromosome 3H to normal levels.

Transcriptional and posttranscriptional regulation of seed storage-protein gene expression in pea (Pisum sativum L.)

At least three classes of legumin, encoded by the gene families legA, legJ and legS, and a lectin, encoded by a single gene, accumulate in the developing cotyledons of Pisum sativum L. Transcription rates for the genes encoding these proteins were measured in nuclei isolated from cotyledons at 12 and 16 days after flowering (DAF). The steady-state levels of the corresponding mRNA species were also measured in absolute terms throughout cotyledon development, from 8-9 to 28 DAF. When transcription rates and steady-state mRNA levels of the different gene families are compared, there is little correlation. This indicates a posttranscriptional regulation of the level of expression of these storage proteins in the developing cotyledons. Expression of the legumin genes is known to be seed-specific, whereas expression of the lectin gene is found in both seed and root. When transcription rates were measured in leaf nuclei the levels of legumin and lectin transcripts detected approached background levels, indicating that these genes are either inactive or transcribed at very low levels in leaves; however, the rate of transcription of the chlorophyll a/b-binding protein gene was high. This points to transcriptional control as the major factor in the organ-specificity of legumin and lectin expression.

Nucleotide sequence and endosperm-specific expression of the structural gene for the toxin alpha-hordothionin in barley (Hordeum vulgare L.)

A barley genomic library, obtained by cloning in the vector lambda EMBL-4, was screened with a cDNA probe encoding the alpha-hordothionin toxin. A positive clone, designated lambda TH1, was selected for further characterization. The coding and flanking regions of the alpha-hordothionin gene (Hth-1) were sequenced. Hth-1 has two introns of 420 and 91 nucleotides (nt), respectively. The promoter region has the following main features: one TATA box; three CATC boxes; an enhancer-like sequence, starting at nt position -282 from the first ATG codon, which is homologous to sequences appearing at similar positions in other endosperm genes; two versions of an 18-nt sequence that is more highly repeated in structural domains of several prolamin genes; two extensive regions close to the first ATG codon that are homologous to a sequence located much further upstream in the B-hordein promoter. The transcription start point was determined at nt positions -46 to -47, both by the S1 nuclease-protection and by the primer-extension assays. A maximum of 2-4 copies of the Hth-1 gene per haploid genome was determined by Southern-blot hybridization. Expression of the Hth-1 gene was detected during the cell proliferation stage of endosperm development (maximum at 13-16 days after pollinization) and was not detected in either etiolated or green coleoptiles.