Em polypeptide and its messenger RNA levels are modulated by abscisic acid during embryogenesis in wheat

Is the Novel Slot Blot a Useful Method for Quantification of Intracellular Advanced Glycation End-Products?

Various types of advanced glycation end-products (AGEs) have been identified and studied. I have reported a novel slot blot analysis to quantify two types of AGEs, glyceraldehyde-derived AGEs, also called toxic AGEs (TAGE), and 1,5-anhydro-D-fructose AGEs. The traditional slot blot method has been used for the detection and quantification of RNA, DNA, and proteins since around 1980 and is one of the more commonly used analog technologies to date. However, the novel slot blot analysis has been used to quantify AGEs from 2017 to 2022. Its characteristics include (i) use of a lysis buffer containing tris-(hydroxymethyl)-aminomethane, urea, thiourea, and 3-[3-(cholamidopropyl)-dimetyl-ammonio]-1-propane sulfonate (a lysis buffer with a composition similar to that used in two-dimensional gel electrophoresis-based proteomics analysis); (ii) probing of AGE-modified bovine serum albumin (e.g., standard AGE aliquots); and (iii) use of polyvinylidene difluoride membranes. In this review, the previously used quantification methods of slot blot, western blot, immunostaining, enzyme-linked immunosorbent assay, gas chromatography-mass spectrometry (MS), matrix-associated laser desorption/ionization-MS, and liquid chromatography-electrospray ionization-MS are described. Lastly, the advantages and disadvantages of the novel slot blot compared to the above methods are discussed.

Modulation of wheat grain dormancy by introducing the recombinant abscisic acid-stimulated abscisic acid biosynthesis gene

Pre-harvest sprouting of cereals greatly reduces yield and quality of the grains. Abscisic acid (ABA) is an essential phytohormone for the induction and maintenance of seed dormancy. In this study, the ABA responsive promoter-driven ABA biosynthesis gene system was introduced to common wheat (Triticum aestivum L.) to enhance ABA production in the embryos and pre-harvest sprouting tolerance of the grains. This system consists of a wheat ABA responsive element containing Early-Methionine-labelled (EM) promoter and a sorghum 9-cis-epoxycarotenoid dioxygenase (SbNCED) gene which encodes an ABA biosynthesis rate-limiting enzyme. Twenty-three independent single-insertion lines were obtained, from which five homozygous lines showing various SbNCED expression levels were selected. Correlations were observed between SbNCED expression, ABA accumulation in the embryos and enhanced dormancy levels of the grains. The engineered wheat grains exhibited a few day-delay in germination, which should be effective in reducing pre-harvest sprouting damage. However, the increase in ABA levels in the recombinant grains was moderate, which explains why germination was not completely suppressed. Further analysis indicated a concomitant increase in the expression of the ABA catabolic enzyme gene TaABA8'OH1 and in the levels of isoleucine-conjugated jasmonic acid, implying the presence of possible negative feedback regulation in the innate system, which should be overcome for future technology development. These findings advance an understanding of the regulatory mechanisms of hormone metabolism in seeds and facilitate the development of pre-harvest sprouting tolerance in cereal grains.

The Interrelationship between Abscisic Acid and Reactive Oxygen Species Plays a Key Role in Barley Seed Dormancy and Germination

Seed dormancy is one of the adaptive responses in the plant life cycle and an important agronomic trait. Reactive oxygen species (ROS) release seed dormancy and promote seed germination in several cereal crops; however, the key regulatory mechanism of ROS-mediated seed dormancy and germination remains controversial. Here, we focused on the relationship between hydrogen peroxide (a ROS) and abscisic acid (ABA) in dormant and non-dormant barley seeds. The hydrogen peroxide (H₂O₂) level produced in barley seed embryos after imbibition was higher in non-dormant seeds than in dormant seeds. H₂O₂ regulated the ABA content in the embryos through ABA-8'-hydroxylase, an ABA catabolic enzyme. Moreover, compared with non-dormant seeds, in dormant seeds the activity of NADPH oxidase, which produces ROS, was lower, whereas the activity of catalase, which is a H₂O₂ scavenging enzyme, was higher, as was the expression of HvCAT2. Furthermore, precocious germination of isolated immature embryos was suppressed by the transient introduction of HvCAT2 driven by the maize (Zea mays) ubiquitin promoter. HvCAT2 expression was regulated through an ABA-responsive transcription factor (HvABI5) induced by ABA. These results suggest that the changing of balance between ABA and ROS is active in barley seed embryos after imbibition and regulates barley seed dormancy and germination.

Changes in hormone flux and signaling in white spruce (Picea glauca) seeds during the transition from dormancy to germination in response to temperature cues

BACKGROUND

Seeds use environmental cues such as temperature to coordinate the timing of their germination, allowing plants to synchronize their life history with the seasons. Winter chilling is of central importance to alleviate seed dormancy, but very little is known of how chilling responses are regulated in conifer seeds. White spruce (Picea glauca) is an important conifer species of boreal forests in the North American taiga. The recent sequencing and assembly of the white spruce genome allows for comparative gene expression studies toward elucidating the molecular mechanisms governing dormancy alleviation by moist chilling. Here we focused on hormone metabolite profiling and analyses of genes encoding components of hormone signal transduction pathways, to elucidate changes during dormancy alleviation and to help address how germination cues such as temperature and light trigger radicle emergence.

RESULTS

ABA, GA, and auxin underwent considerable changes as seeds underwent moist chilling and during subsequent germination; likewise, transcripts encoding hormone-signaling components (e.g. ABI3, ARF4 and Aux/IAA) were differentially regulated during these critical stages. During moist chilling, active IAA was maintained at constant levels, but IAA conjugates (IAA-Asp and IAA-Glu) were substantially accumulated. ABA concentrations decreased during germination of previously moist-chilled seeds, while the precursor of bioactive GA1 (GA53) accumulated. We contend that seed dormancy and germination may be partly mediated through the changing hormone concentrations and a modulation of interactions between central auxin-signaling pathway components (TIR1/AFB, Aux/IAA and ARF4). In response to germination cues, namely exposure to light and to increased temperature: the transfer of seeds from moist-chilling to 30 °C, significant changes in gene transcripts and protein expression occurred during the first six hours, substantiating a very swift reaction to germination-promoting conditions after seeds had received sufficient exposure to the chilling stimulus.

CONCLUSIONS

The dormancy to germination transition in white spruce seeds was correlated with changes in auxin conjugation, auxin signaling components, and potential interactions between auxin-ABA signaling cascades (e.g. the transcription factor ARF4 and ABI3). Auxin flux adds a new dimension to the ABA:GA balance mechanism that underlies both dormancy alleviation by chilling, and subsequent radicle emergence to complete germination by warm temperature and light stimuli.

A wheat homolog of MOTHER OF FT AND TFL1 acts in the regulation of germination

Seed dormancy is an adaptive mechanism and an important agronomic trait. Temperature during seed development strongly affects seed dormancy in wheat (Triticum aestivum) with lower temperatures producing higher levels of seed dormancy. To identify genes important for seed dormancy, we used a wheat microarray to analyze gene expression in embryos from mature seeds grown at lower and higher temperatures. We found that a wheat homolog of MOTHER OF FT AND TFL1 (MFT) was upregulated after physiological maturity in dormant seeds grown at the lower temperature. In situ hybridization analysis indicated that MFT was exclusively expressed in the scutellum and coleorhiza. Mapping analysis showed that MFT on chromosome 3A (MFT-3A) colocalized with the seed dormancy quantitative trait locus (QTL) QPhs.ocs-3A.1. MFT-3A expression levels in a dormant cultivar used for the detection of the QTL were higher after physiological maturity; this increased expression correlated with a single nucleotide polymorphism in the promoter region. In a complementation analysis, high levels of MFT expression were correlated with a low germination index in T1 seeds. Furthermore, precocious germination of isolated immature embryos was suppressed by transient introduction of MFT driven by the maize (Zea mays) ubiquitin promoter. Taken together, these results suggest that MFT plays an important role in the regulation of germination in wheat.

Isolation and characterization of a cDNA clone encoding wheat germ agglutinin

Two sets of synthetic oligonucleotides coding for amino acids in the amino- and carboxyl-terminal portions of wheat germ agglutinin were synthesized and used as hybridization probes to screen cDNA libraries derived from developing embryos of tetraploid wheat. The nucleotide sequence for a cDNA clone recovered from the cDNA library was determined by dideoxynucleotide chain-termination sequencing in vector M13. The amino acid sequence deduced from the DNA sequence indicated that this cDNA clone (pNVR1) encodes isolectin 3 of wheat germ agglutinin. Comparison of the deduced amino acid sequence of clone pNVR1 with published sequences indicates isolectin 3 differs from isolectins 1 and 2 by 10 and 8 amino acid changes, respectively. In addition, the protein encoded by pNVR1 extends 15 amino acids beyond the carboxyl terminus of the published amino acid sequence for isolectins 1 and 2 and includes a potential site for N-linked glycosylation. Utilizing the insert of pNVR1 as a hybridization probe, we have demonstrated that the expression of genes for wheat germ agglutinin is modulated by exogenous abscisic acid. Striking homology is observed between wheat germ agglutinin and chitinase, both of which are proteins that bind chitin.

Analysis of promoters in transgenic barley and wheat

Advances in the genetic transformation of cereals have improved the prospects of using biotechnology for plant improvement, and a toolbox of promoters with defined specificities would be a valuable resource in controlling the expression of transgenes in desired tissues for both plant improvement and molecular farming. A number of promoters have been isolated from the important cereals (wheat, barley, rice and maize), and these promoters have been tested mostly in homologous cereal systems and, to a lesser extent, in heterologous cereal systems. The use of these promoters across the important cereals would add value to the utility of each promoter. In addition, promoters with less sequence homology, but with similar specificities, will be crucial in avoiding homology-based gene silencing when expressing more than one transgene in the same tissue. We have tested wheat and barley promoters in transgenic barley and wheat to determine whether their specificity is shared across these two species. The barley bifunctional alpha-amylase/subtilisin inhibitor (Isa) promoter, specific to the pericarp in barley, failed to show any activity in wheat, whereas the wheat early-maturing (Em) promoter showed similar activity in wheat and barley. The wheat high-molecular-weight glutenin (HMW-Glu) and barley D-hordein (D-Hor) and B-hordein (B-Hor) storage protein promoters maintained endosperm-specific expression of green fluorescent protein (GFP) in wheat and barley, respectively. Using gfp, we have demonstrated that the Isa and Em promoters can be used as strong promoters to direct transgenes in specific tissues of barley and wheat grain. Differential promoter activity across cereals expands and adds value to a promoter toolbox for utility in plant biotechnology.

The evolution of the abscisic acid-response in land plants: comparative analysis of group 1 LEA gene expression in moss and cereals

The moss Physcomitrella patens possesses a single copy of a Group 1 LEA gene, designated PpLEA-1. Sequence analysis of the PpLEA-1 gene reveals the gene to contain a single intron in a position conserved in all members of the Group 1 LEA gene family, but also to contain a premature termination codon within the first exon. Nevertheless, a PpLEA-1 transcript accumulates in moss tissues in response both to the imposition of osmotic stress, and to the plant growth regulator abscisic acid (ABA). This response appears to be mediated at the transcriptional level, and observation of the pattern of gene expression, reported by histochemical staining of plants expressing a PpLea-1::GUS transgene suggests that the promoter responds preferentially to ABA in protonemal filaments, whereas osmotic stress induces gene expression primarily in the gametophores. Quantitative analysis of promoter activity by transient expression in Physcomitrella protoplasts shows the PpLEA-1 promoter to be highly active in response to ABA and osmotic stress. ABA-mediated transgene expression from the PpLea-1 promoter occurs at a level similar to that driven by the highly active promoter of the wheat Group 1 LEA gene, E(m). Site-directed mutagenesis of the PpLEA-1 promoter indicates that ABA-inducibility is mediated via an ACGT-core motif similar to that seen in the ABA response elements of higher plant LEA genes. However, whereas the wheat E(m )promoter is active in moss tissues, the moss promoter is not reciprocally active in cereal cells: no activity, ABA-inducible or otherwise was detected in barley aleurone protoplasts transfected with the PpLEA-1::GUS construct. We propose that ABA activation of gene expression in moss cells represents an ancestral state, with only minimal requirements for promoter recognition, whereas cereal cells require the interaction of additional factors with ABA-responsive promoters.

The wheat Em promoter drives reporter gene expression in embryo and aleurone tissue of transgenic barley and rice

The early methionine (Em) proteins are members of the late embryogenesis abundant (LEA) group of proteins that have been considered to be embryo specific. The ability of a 646-bp wheat Em promoter to control green fluorescent protein (gfp) expression was investigated in transgenic barley and rice. Seeds of transgenic plants expressed gfp in the developing embryo but also in the aleurone layer. The 646-bp Em promoter also directed strong gfp expression in cells comprising the junction between the endosperm transfer cells and cells of the aleurone layer. Em-gfp expression in transgenic barley showed differences in spatial and temporal control when compared with that observed in transgenic rice. Em-gfp expression was also detected in mature aleurone cells of transgenic barley and rice with and without abscisic acid (ABA) treatment. Reverse transcriptase-polymerase chain reaction (RT-PCR) results indicated the presence of Em and Em-homologous transcript in embryo, aleurone and endosperm tissues of wheat and of barley and rice, respectively. These results suggest that Em proteins may be expressed in both the embryo and aleurone during seed development, possibly providing protection against desiccation in these two tissues that survive seed drying. They may also have a similar role in these tissues during germination. The Em promoter from wheat may be useful in the expression of novel genes in cereal grains, as an embryo- and aleurone-specific promoter complementing other available endosperm- and pericarp-specific promoters to collectively increase the expression of transgenes in seeds.

Isolation and localization of new germination-related sequences from wheat embryos

Subtractive library hybridization was used to isolate the cDNA clones that corresponded to the transcripts that were specifically up-regulated during wheat embryo germination. The clones with numbers 5, 6, 7, 8, 24, and 26 appeared to be more abundant in germinating wheat embryos. Among the isolated clones, we identified four new members of the wheat "germin" gene family. We also identified two novel sequences which exhibited distinct germination up-regulation, and displayed characteristic spatial patterns of expression. One of these, represented by clone pSB10, was principally expressed in the root tissue of germinating embryos. The second was represented by the pSB7 clone and was expressed in both the root and shoot primordia of the embryonic axis, as well as within the coleoptile.

Increased dehydrin promoter activity caused by HvSPY is independent of the ABA response pathway

A barley SPINDLY protein, HvSPY, is a negative regulator of gibberellin (GA) action. It is also found to be a positive regulator of the promoter of a barley dehydrin (Dhn) gene which is abscisic acid (ABA) upregulated. To investigate whether HvSPY acts through the ABA signaling pathway to upregulate the Dhn promoter, functional characterization was carried out by co-bombardment experiments. These experiments used Dhn promoter-GUS reporter constructs and an effector construct to overexpress HvSPY protein in barley aleurone. ABA dose-response experiments with and without HvSPY overexpression showed that the induction by HvSPY occurred in addition to the ABA effect. Gibberellic acid (GA3) did not reduce the induction by ABA, but it had a small, although significant, effect on the ability of HvSPY to upregulate. The induction of promoter activity of Dhn by HvSPY required the intact protein, and a small deletion in the tetratricopeptide repeat (TPR) region reduced this ability significantly. When a promoter region containing an element for ABA responsiveness was mutagenized or deleted, the mutant promoters lost ABA responsiveness but remained responsive to HvSPY. In addition, HvSPY did not increase promoter activities of other ABA-upregulated genes. Taken together, these results indicate that HvSPY and ABA both regulate promoter activity of Dhn, and that HvSPY acts independently of the ABA signaling pathway.

Regulation of Arabidopsis thaliana Em genes: role of ABI5

In order to identify new factors involved in Em (a class I Late Embryogenesis Abundant protein) gene expression, Arabidopsis mutants with an altered expression of an Em promoter GUS fusion construct and a modified accumulation of Em transcripts and proteins were isolated. Germination tests on ABA showed that the most affected mutant had a weak abi phenotype. Complementation tests further revealed this mutant to be a new abi5 allele, consequently named abi5-5. In addition to reducing the final level of Em transcripts in the dry seed, the abi5-5 mutation causes a delay in the accumulation of AtEm1 during seed development. An additional characteristic of the abi5-5 mutant, is the ability of its seeds to germinate at high concentrations of salt and mannitol. The abi5-5 mutation was characterized at the molecular level and was shown to result from a two base pair deletion in the coding sequence of the ABI 5 gene. The wild type and mutant recombinant proteins were produced in E. coli and were assayed for DNA-binding activity on their target promoters by electrophoretic mobility shift assay (EMSA). The ABI5 recombinant protein binds the ABRE sequence in the AtEm6 promoter as shown by Dnase footprinting. Among the ABRE-type sequences selected on both Em promoters, the G-box type AGACACGTGGCATGT element of the AtEm6 promoter shows the strongest binding by EMSA quantification.

Two structurally similar maize cytosolic superoxide dismutase genes, Sod4 and Sod4A, respond differentially to abscisic acid and high osmoticum

The maize (Zea mays) superoxide dismutase genes Sod4 and Sod4A are highly similar in structure but each responds differentially to environmental signals. We examined the effects of the hormone abscisic acid (ABA) on the developmental response of Sod4 and Sod4A. Although both Sod4 and Sod4A transcripts accumulate during late embryogenesis, only Sod4 is up-regulated by ABA and osmotic stress. Accumulation of Sod4 transcript in response to osmotic stress is a consequence of increased endogenous ABA levels in developing embryos. Sod4 mRNA is up-regulated by ABA in viviparous-1 mutant embryos. Sod4 transcript increases within 4 h with ABA not only in developing embryos but also in mature embryos and in young leaves. Sod4A transcript is up-regulated by ABA only in young leaves, but neither Sod4 nor Sod4A transcripts changed in response to osmotic stress. Our data suggest that in leaves Sod4 and Sod4A may respond to ABA and osmotic stress via alternate pathways. Since the Sod genes have a known function, we hypothesize that the increase in Sod mRNA in response to ABA is due in part to ABA-mediated metabolic changes leading to changes in oxygen free radical levels, which in turn lead to the induction of the antioxidant defense system.

PCR-based isolation and chromosome assignment of members of the Em gene family from wheat

Four members belonging to the wheat Em gene family were isolated by PCR, cloned and subsequently sequenced. One of the genes corresponds perfectly to a previous published cDNA sequence, the other three genes are new. The amplified sequences contain the entire coding region, which is interrupted by a short intron of variable length, and part of the 3' untranslated region. The chromosomal assignment of each of the four sequences and three extra, previously published, Em sequences was determined using PCR with sequence-specific primers on wheat aneuploid nullitetrasomic lines. Three sequences were shown to be encoded by the Em-A1 locus (on chromosome 1A), one by Em-B1 on chromosome 1B and two by Em-D1 on chromosome 1D. Hence, primer sets specific for each of the three homoeologous chromosomes of the group 1 are available. A lot of DNA sequence polymorphism exists among the sequences most of which is found in the non-coding parts and mainly in the introns. Sequence alignment groups the seven known Em sequences irrespective of their locus origin. The implication of these findings in relation to the organisation and evolution of the Em gene family are discussed.

Tissue-specific and ABA-regulated Maize GIN gene expression in transgenic tobacco

To study the regulatory functions of the ON promoter region, a ppG1b1GUS construct, consisting of 1402 bp 5' flanking sequence ofGlbl, 1919 by GUS coding sequence, and 283 by 3' NOS terminator, was cloned into a binary vector and introduced into tobacco plants byAgrobacterium-mediated transformation. Histochemical GUS assays of To tobacco mature seeds indicate that theGlbl promoter drives GUS expression in ABA treated seeds. Further GUS assays of the T, seeds at different developmental stages revealed that without ABA treatment, theGibl promoter drives GUS expression in immature seeds. The results from both To and T1 tobacco plants indicated thatGlbl-driven GUS expression in tobacco is embryo specific.

cDNA encoding a wheat (Triticum aestivum cv. Chinese spring) glycine-rich RNA-binding protein

A wheat cDNA encoding a glycine-rich RNA-binding protein, whGRP-1, was isolated. WhGRP-1 contains two conserved domains, the RNA-binding motif (RNP motif) combined with a series of glycine-rich imperfect repeats, characteristic of a conserved family of plant RNA-binding proteins. Northern analysis revealed that whGRP-1 mRNA accumulates to high levels in roots and to lower levels in leaves of wheat seedlings, whGRP-1 mRNA accumulation is not enhanced by exogenous abscisic acid in seedlings and accumulates to very high levels during wheat embryo development, showing a pattern different from that of the ABA-inducible wheat Em gene.

A distinctly regulated protein repair L-isoaspartylmethyltransferase from Arabidopsis thaliana

Protein-L-isoaspartate (D-aspartate) O-methyltransferases (EC 2.1.1.77) that catalyze the transfer of methyl groups from S-adenosylmethionine to abnormal L-isoaspartyl and D-aspartyl residues in a variety of peptides and proteins are widely distributed in procaryotes and eucaryotes. These enzymes participate in the repair of spontaneous protein damage by facilitating the conversion of L-isoaspartyl and D-aspartyl residues to normal L-aspartyl residues. In this work, we have identified an L-isoaspartyl methyltransferase activity in Arabidopsis thaliana, a dicotyledonous plant of the mustard family. The highest levels of activity were detected in seeds. Using degenerate oligonucleotides corresponding to two highly conserved amino acid regions shared among the Escherichia coli, wheat, and human enzymes, we isolated and sequenced a full-length genomic clone encoding the A. thaliana methyltransferase. Several methyltransferase cDNAs were also characterized, including ones that would encode full-length polypeptides of 230 amino acid residues. Messenger RNAs for the A. thaliana enzyme were found in a variety of tissues that did not contain significant amounts of active enzyme suggesting the possibility of translational or posttranslational controls on methyltransferase levels. We have identified a putative abscisic acid-response element (ABRE) in the 5'-untranslated region of the A. thaliana L-isoaspartyl methyltransferase gene and have shown that the expression of the mRNA is responsive to exogenous abscisic acid (ABA), but not to the environmental stresses of salt or drought. The expression of the A. thaliana enzyme appears to be regulated in a distinct fashion from that seen in wheat or in animal tissues.

Linkage relationships among stress-induced genes in wheat

Linkage relationships among genes responding to water-deficit, salt stress, and heat shock were investigated in diploid wheat, Triticum monococcum L. The position of these gene loci relative to closely linked markers and the centromeres is reported. It is proposed to continue to use the present T. monococcum mapping population and the genetic maps based thereon as a framework for future determination of relationships among other genes related to environmental stress in the tribe Triticeae.

Sequence analysis of a mannitol dehydrogenase cDNA from plants reveals a function for the pathogenesis-related protein ELI3

Mannitol is the most abundant sugar alcohol in nature, occurring in bacteria, fungi, lichens, and many species of vascular plants. Celery (Apium graveolens L.), a plant that forms mannitol photosynthetically, has high photosynthetic rates thought to results from intrinsic differences in the biosynthesis of hexitols vs. sugars. Celery also exhibits high salt tolerance due to the function of mannitol as an osmoprotectant. A mannitol catabolic enzyme that oxidizes mannitol to mannose (mannitol dehydrogenase, MTD) has been identified. In celery plants, MTD activity and tissue mannitol concentration are inversely related. MTD provides the initial step by which translocated mannitol is committed to central metabolism and, by regulating mannitol pool size, is important in regulating salt tolerance at the cellular level. We have now isolated, sequenced, and characterized a Mtd cDNA from celery. Analyses showed that Mtd RNA was more abundant in cells grown on mannitol and less abundant in salt-stressed cells. A protein database search revealed that the previously described ELI3 pathogenesis-related proteins from parsley and Arabidopsis are MTDs. Treatment of celery cells with salicylic acid resulted in increased MTD activity and RNA. Increased MTD activity results in an increased ability to utilize mannitol. Among other effects, this may provide an additional source of carbon and energy for response to pathogen attack. These responses of the primary enzyme controlling mannitol pool size reflect the importance of mannitol metabolism in plant responses to divergent types of environmental stress.

Differentiation between homoeologous chromosomes 1A of wheat and 1Am of Triticum monococcum and its recognition by the wheat Ph1 locus

In most allopolyploid plants, only homogenetic chromosome pairing occurs in meiosis, as a result of the recognition of genome differentiation by the genetic system regulating meiotic chromosome pairing. The nature of differentiation between chromosomes of closely related genomes is examined here by investigating recombination between wheat chromosome 1A and the closely related homoeologous chromosome 1Am of Triticum monococcum. The recognition of the differentiation between these chromosomes by the Ph1 locus, which prevents heterogenetic chromosome pairing in wheat, is also investigated. Chromosomes 1A and 1Am are shown to be colinear, and it is concluded that they are differentiated "substructurally." This substructural differentiation is argued to be recognized by the Ph1 locus. In the absence of Ph1, the distribution and frequencies of crossing over between the 1A and 1Am homoeologues were similar to the distribution and frequencies of crossing over between 1A homologues. The cytogenetic and evolutionary significance of these findings is discussed.

Sequence analysis of two tandemly linked Em genes from wheat

DNA sequences are presented for two members of the wheat Em gene family. The sequences correspond to the two linked genes at the Xem-1AL locus. Comparisons of these sequences with that of another wheat Em gene and two Em cDNA clones reveals substantial homology within the protein-coding regions, and the presence in the 5'-flanking regions of the genomic sequences of motifs characteristic of ABA-responsive cis-acting elements.

Selective proteolysis of the wheat Em polypeptide. Identification of an endopeptidase activity in germinating wheat embryos

The 'Em' polypeptide is the most abundant cytosolic polypeptide in mature wheat embryos. It is selectively and completely degraded within the first 24 h of germination. Extracts from germinated embryos contain endopeptidase activities which degrade the Em polypeptide. These are separable into a major and minor component by ion-exchange chromatography and the use of inhibitors shows the major component to be a cysteine proteinase. This activity shows a strong preference for the Em polypeptide as a substrate, being inactive against polypeptides which are not developmentally regulated and showing only low activity towards developmentally related, but otherwise nonhomologous 'dehydrin' polypeptides.

Purification of an endoproteinase that digests the wheat 'Em' protein in vitro, and determination of its cleavage sites

Germinating wheat embryos contain two endoproteolytic activities which digest the prominent 'Em' polypeptide. These are easily assayed in clarified embryonic homogenates and are distinguishable by the pattern of their peptide products and by their different pH optima. One activity has a pH optimum of 4.0; the second activity is a cysteine endoproteinase with a preference for the 'Em' protein as its substrate. It is maximally active between pH 5.5 and 6 at 25 degrees C. Analysis of the early cleavage products of the cysteine proteinase indicates scissile bonds between residues Glu32-Ala33 and Asn36-Leu37 in the 'Em' polypeptide. This endoproteinase has been purified and identified as a single polypeptide species of ca. 38,000 kDa.

Abscisic acid-insensitive mutations provide evidence for stage-specific signal pathways regulating expression of an Arabidopsis late embryogenesis-abundant (lea) gene

An Arabidopsis homolog of the abscisic acid (ABA)-inducible cotton D19 and wheat Em genes was cloned and its expression assayed at two developmental stages in wild-type, ABA-deficient (aba) and three ABA-insensitive (abi) lines of Arabidopsis thaliana. Expression of this gene was reduced slightly in seeds of aba mutants and approximately ten-fold in abi3 mutants, but seed expression was not decreased in either abi1 or abi2 monogenic mutants. In contrast, the abi1 and abi2 mutants showed a very slight reduction of ABA inducibility in 8-day-old plants, while the responses of aba and abi3 mutants were comparable to that of wild type. Although previous studies have shown that none of the abi mutations show completely stage-specific effects, the results reported here indicate that the importance of each of the ABI loci in regulating this single gene is stage-dependent. Furthermore, the fact that none of the abi mutations show more than minor effects on exogenous ABA inducibility of the Arabidopsis D19/Em homolog in young plants suggests that an additional ABA signalling pathway may be operating during vegetative growth.

Two different Em-like genes are expressed in Arabidopsis thaliana seeds during maturation

Using a radish cDNA probe, we have isolated and characterized two genomic clones from Arabidopsis thaliana (GEA1 and GEA6) encoding two different proteins that are homologous to the "Early methionine-labelled" (Em) protein of wheat. GEA1 differs from GEA6 and Em clones of wheat in that a sequence coding for 20 amino acid residues is tandemly repeated 4 times. These two genomic clones correspond to two genes named AtEm1 and AtEm6. Sequencing of several cDNA clones showed that both genes are expressed. The transcription start site was determined for both genes by RNase mapping. The site of polyadenylation is variable and there is no obvious consensus sequence for polyadenylation at the 3' ends of the genes. mRNA corresponding to GEA6 is present only in nearly dry and dry seeds, whereas the corresponding to GEA1 appears in immature seeds and is maximum in dry seeds. No expression of either gene could be detected in leaf, stem, or floral buds. Expression of both genes could be detected in immature seeds when the siliques were incubated with abscisic acid (ABA), demonstrating that both genes are ABA responsive. However, examination of the 5' upstream region does not reveal any extensive homology, suggesting that regulation of the two genes differs. In situ hybridization with a GEA1 probe demonstrated that the expression of this gene is essentially located in the provascular tissues of the cotyledons and axis of the dry seed as well as in the epiderm and outer layers of the cortex in the embryo axis.

Germin isoforms are discrete temporal markers of wheat development. Pseudogermin is a uniquely thermostable water-soluble oligomeric protein in ungerminated embryos and like germin in germinated embryos, it is incorporated into cell walls

Nascent synthesis and accumulation of germin and its mRNA mark the onset of renewed growth when wheat embryos are germinated in water. Germin is a water-soluble, pepsin-resistant protein that is not found in immature embryos, or in mature embryos before their germination. An antiserum was raised by injecting rabbits with germin that was freed of other proteins by pepsinization and gel filtration. The antiserum has been used to detect, in extracts of mature embryos from dry, ungerminated wheat grains, a protein that is antigenically related to germin. The antigenically related protein has been named pseudogermin. Pseudogermin accumulates, maximally, between 20-25-days postanthesis, then declines appreciably in amount by 30-days postanthesis, in soluble extracts of immature embryos from several wheat varieties. The antiserum was also used to identify germin and pseudogermin among the proteins extracted from cell walls and to bind immunogold to cell walls preparatory to visualizing freeze-cleaved embryos by scanning electron microscopy. Wall-associated germin accounts for about 40% of the total germin in germinating wheat embryos. Appearance of germin in the apoplast is the most conspicuous germination-related change in the distribution of cell-wall proteins. It seems that germin may act at the level of the apoplast and that pseudogermin may subsume the role of germin at low water potentials during embryogenesis. The N-terminal eicosapeptide sequences in germin and pseudogermin are very similar but SDS/PAGE analysis detects discrete differences between the mobilities of their constituent monomers as well as gross differences between the stabilities of the parent oligomers. Like germin, pseudogermin is a water-soluble, pepsin-resistant protein, but pseudogermin has unprecedented disulphide-independent thermostability properties that have never been previously reported for a water-soluble oligomeric protein. Polysaccharides that co-purify with otherwise pure specimens of germin (and pseudogermin) have been isolated for analysis and shown to be highly substituted glucuronogalactoarabinoxylans. The possible biological significance of selective and tenacious association between germin and glucuronogalactoarabinoxylans is discussed in relation to cell expansion during embryogenic and germinative development of wheat, as are some peculiarities of amino-acid sequence that suggest a possible relation between germin and a proton-specific ion pump: gastric ATPase.

Wheat Ec metallothionein genes. Like mammalian Zn2+ metallothionein genes, wheat Zn2+ metallothionein genes are conspicuously expressed during embryogenesis

A cDNA library was prepared from the bulk mRNA of mature wheat embryos and screened with mixed 32P-labeled oligonucleotide probes that encoded parts of the partial amino-acid sequence for the Zn-containing Ec protein. Each DNA insert in 11 positives from a screen of 10(5) plaques encoded a 5' untranslated and a 3' untranslated region, in addition to an open reading frame (of 81 amino acids) which, in every case, corresponded to at least 56 of the 59 amino acids in the partial polypeptide sequence previously determined for the Ec protein. The three different mRNA sequences encoded in the cDNA probably correspond to single-copy genes in the A, B and D genomes of hexaploid wheat. A wheat genomic library was screened with 32P-labeled cDNA and gave a single positive in a screen of 5 x 10(5) plaques. A 3.1-kb genomic fragment (gf-3.1) was sequenced and a cap site for the encoded mRNA was determined by primer extension. The gf-3.1 sequence encodes an intronless mRNA for the Ec protein and contains appreciable amounts of 5' and 3' flanking sequences. In addition to a putative TATA box, two inverted-repeat sequences and one direct-repeat sequence, the 5' flank in gf-3.1 contains a sequence similar to the abscisic-acid-responsive element in other higher-plant genes but does not contain sequences similar to the metal-responsive elements in animal metallothionein genes. Consistent with these findings, RNA blotting shows that accumulation of Ec mRNA is abundant in immature embryos, undetectable in germinated embryos and can be induced by adding abscisic acid, but not by adding Zn2+ to the medium in which mature wheat embryos are germinated. The findings suggest that the wheat Ec metallothionein genes, like mammalian liver metallothionein genes, are conspicuously expressed during embryogenesis.

Differential response of maize catalases to abscisic acid: Vp1 transcriptional activator is not required for abscisic acid-regulated Cat1 expression

In this paper we describe the distinctive responses of the maize catalases to the plant growth regulator abscisic acid (ABA). We analyzed RNA and enzyme accumulation in excised maize embryos and found that each catalase responded differently to exogenously applied ABA. Levels of Cat1 transcript and enzyme activity rapidly increased. In contrast, levels of Cat2 transcript and protein decreased, while Cat3 transcript levels were not affected. In developing kernels of the ABA-deficient/biosynthetic viviparous mutant vp5, lower levels of Cat1 RNA correlated with lower endogenous ABA levels when compared to measured levels in comparably aged wild-type siblings from the same ear. The maize vp1 mutant line is morphologically insensitive to normal endogenous levels of ABA. Analysis of the response of Cat1 to exogenously applied ABA in mutant and wild-type vp1 sibling embryos suggests that, unlike other ABA-responsive genes analyzed to date, the Vp1 gene product is not essential for the ABA-mediated regulation of Cat1. The significance of these responses to ABA in defining the roles of the various CATs in maize is discussed.

Developmental and environmental concurrent expression of sunflower dry-seed-stored low-molecular-weight heat-shock protein and Lea mRNAs

We have cloned and sequenced three different cDNAs from sunflower seed-stored mRNA. Sequence similarities and response to heat-shock identified one of the cDNAs as a low-molecular-weight heat-shock protein (lmw-HSP). The other two clones showed significant sequence similarity to the cotton and carrot late-embryogenesis-abundant (Lea) proteins D-113 and Emb-1, respectively. The three cDNAs showed similar expression patterns during zygotic embryo development, as well as in vegetative tissues of 3-day-old seedlings in response to stress. Maximal accumulation of all three mRNAs was detected in dry seeds and during embryo mid-maturation stage, in the absence of exogenous stress. In seedlings, mRNAs accumulated to lower levels in response to osmotic stress and exogenous abscisic acid (ABA) treatments. A differential time course of response to osmotic stress was observed: lmw-HSP mRNA accumulation was induced earlier than that of Lea mRNAs. The coordinate accumulation of Lea and lmw-HSP transcripts during embryo development and in response to stress and ABA suggests the existence of common regulatory elements for Lea and lmw-HSP genes, and supports the notion that HSPs might have alternative functions in the plant cell.

Comparative RFLP-based genetic maps of barley chromosome 5 (1H) and rye chromosome 1R

A genetic map of barley chromosome 5 (1H) was constructed using DNA markers. Seventeen loci were mapped to 15 locations, and these included the known-function loci (in order from the most distal on the long arm) XAdh (alcohol dehydrogenase), XLec (homologous to wheat germ agglutinin), XHor3 (D-hordein), XPpdk (pyruvate orthophosphate dikinase), centromere, XIcal (chymotrypsin inhibitor), and 6 loci in the B- and C-hordein cluster towards the end of the short arm. The gene order on the barley map agreed closely with that of chromosome 1 of rye. Intervarietal comparisons showed that single-copy cDNA and genomic DNA probes revealed about twice the level of RFLPs found in wheat.

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.

Mechanisms of action of abscisic acid at the cellular level

Abscisic acid (ABA) has been implicated in the control of a diverse range of physiological processes in higher plants. In this review, we focus on the events which constitute the cellular responses to ABA. Current evidence suggests that it is possible to classify the responses to ABA on the basis of whether they are rapid, involving ion fluxes (typified by the stomatal response), or slower and requiring alterations to gene expression (for example the response of cereal embryos to ABA). In our consideration of ABA stimulus response coupling pathways, we have chosen to highlight the role of the calcium ion in the rapid responses, while we have concentrated on the contribution of as-acting elements and trans-acting factors in the regulation of ABA-responsive genes. We also draw attention to the possibility that interaction may exist between these pathways. Additionally, we discuss the controls of ABA concentrations during development and in response to environmental stimuli. Factors which contribute to the controls of ABA sensitivity are also reviewed. In our conclusions, we suggest that a general role for ABA may be to prepare tissue for entry into a new and different physiological state, perhaps by resetting the direction of cellular metabolism. CONTENTS Summary 9 I. Introduction 10 II. Stimulus response coupling 17 Synopsis 27 Acknowledgements 28 References 28.

RFLP-based genetic map of rye (Secale cereale L.) chromosome 1R

A map of chromosome 1R of rye was constructed using 16 molecular and biochemical loci. From long arm to short arm, known-function loci were placed in the order: XAdh - XLee - Glu-R1[Sec-3] - XPpdk-1R - XEm-1R-1 - XEm-1R-2 - Centromere - XNor-R1 -Gpi-R1 - XGli-R1 [Sec-1a] along with six anonymous genomic and cDNA clones from wheat. The map, which spans 106 cM with 12 loci clustered in a 15-cM region around the centromere, shows reasonably good agreement with previously published maps for the centromeric region, whereas the XNor-R1 - Gpi-R1 region gives a much larger distance than previously reported.

An embryo-specific protein of barley (Hordeum vulgare)

An immunological approach has been used to identify embryo-specific products that can be used as molecular markers of embryogenesis. Immunoadsorption of antisera to remove antigens common to embryos, meristematic cells and callus, revealed one major embryo-specific antigen, a polypeptide of 17 kDa. The antigen appeared at mid-stages of zygotic embryo formation and remained at similar levels up to six days post-germination of the seedling. The polypeptide could not be detected by protein staining, suggesting it is a non-abundant product. Appearance of the antigen could be induced by culture of zygotic embryos in vitro on abscisic acid (1 microM) or mannitol (9% mass/vol.). Cross-reactive products of near-identical molecular mass were observed in embryos of wheat, rye and oats but not distantly related cereals, nor embryos from dicotyledonous species. The timing of the appearance of the antigen was different in embryos formed from microspores during anther culture in vitro. In the cultured material, the 17-kDa polypeptide preceded the appearance of morphologically distinct embryonic structure.

Sequence analysis of a functional member of the Em gene family from wheat

We report the complete sequence of one functional member of the Em gene family whose expression in wheat embryos is regulated by a complex set of environmental and developmental controls, including the phytohormone abscisic acid (ABA). The Em coding region contains one short intron, and there is an inverted repeat in the transcribed 3'-flanking region. A 646 bp fragment from the 5' promoter, which was previously shown to direct ABA-regulated expression in transformed tobacco tissue and rice cells, is characterized by: (1) three stretches of between 33 and 73 nucleotides of A/T rich (greater than 86%) boxes, (2) one copy of an eight bp palindrome (CATGCATG) which is identical to the RY repeat found in the 5' promoters of many legume genes expressed during embryo development, (3) 15 copies of a six bp repeat (PuCACGPy), found primarily in the 5' region, and (4) two sequences in the ABA-response region, CGAGCAG and a CACGT motif, both of which are conserved in 5' non-coding regions of other plant genes that are expressed in response to ABA and/or in embryos. These sequence comparisons are discussed in relation to the regulation of Em gene expression and other ABA-regulated genes.

Abscisic acid and osmoticum prevent germination of developing alfalfa embryos, but only osmoticum maintains the synthesis of developmental proteins

Developing seeds of alfalfa (Medicago sativa L.) acquire the ability to germinate during the latter stages of development, the maturation drying phase. Isolated embryos placed on Murashige and Skoog medium germinate well during early and late development, but poorly during mid-development; however, when placed on water they germinate well only during the latter stage of development. Germination of isolated embryos is very slow and poor when they are incubated in the presence of surrounding seed structures (the endosperm or seed coat) taken from the mid-development stages. This inhibitory effect is also achieved by incubating embryos in 10(-5) M abscisic acid (ABA). Endogenous ABA attains a high level during mid-development, especially in the endosperm. Seeds developing in pods treated with fluridone (1-methyl-3-phenyl-5[3-(trifluoromethyl)-phenyl]-4(1H)-pyridinone) contain low levels of ABA during mid-development, and the endosperm and seed coat only weakly inhibit the germination of isolated embryos. However, intact seeds from fluridone-treated pods do not germinate viviparously, which is indicative that ABA alone is not responsible for maintaining seeds in a developing state. Application of osmoticum (e.g. 0.35 M sucrose) to isolated developing embryos prevents their germination. Also, in the developing seed in situ the osmotic potential is high. Thus internal levels of osmoticum may play a role in preventing germination of the embryo and maintaining development. Abscisic acid and osmoticum impart distinctly different metabolic responses on developing embryos, as demonstrated by their protein-synthetic capacity. Only in the presence of osmoticum do embryos synthesize proteins which are distinctly recognizable as those synthesized by developing embryos in situ, i.e. when inside the pod. Abscisic acid induces the synthesis of a few unique proteins, but these arise even in mature embryos treated with ABA. Thus while both osmoticum and ABA prevent precocious germination, their effects on the synthetic capacity of the developing embryo are quite distinct. Since seeds with low endogenous ABA do not germinate, osmotic regulation may be the more important of these two factors in controlling seed development.

Osmotic stress and abscisic acid induce expression of the wheat Em genes

The early-methionine-labelled (Em) polypeptide is the single most abundant cytosolic protein of dry wheat embryos. It is encoded by messenger RNA which accumulates during the later (maturation) stages of embryogenesis. The accumulation of Em mRNA can be induced in isolated developing embryos, in culture, by the application of the plant growth regulator, abscisic acid, which prevents precocious germination. Precocious germination is also inhibited by the culture of embryos under conditions of osmotic stress when accumulation of Em mRNA is induced. This induction occurs in the absence of any significant increase in the endogenous levels of embryonic abscisic acid although there is a requirement for the continued presence of the growth regulator. Additionally, expression of Em genes can be repeated during early germination, if imbibing embryos are subjected to osmotic stress. Induction of Em-gene expression by osmotic stress is consistent with the proposed role of the Em polypeptide in mediating the remarkable tolerance of cereal embryos to the programmed desiccation undergone during their maturation.

Molecular cloning and chromosomal location of genes encoding the "Early-methionine-labelled" (Em) polypeptide of Triticum aestivum L. var. Chinese Spring

The "Early-methionine-labelled" (Em) polypeptide is the most abundant cytosolic polypeptide found in mature wheat embryos. Using a near full-length cDNA clone as a hybridisation probe to detect genomic sequences by Southern blotting of electrophoretic separations of genomic DNA derived from Triticum aestivum L. var. Chinese Spring and a series of its aneuploid derivatives, we demonstrate that the Em polypeptide is the product of a small multigene family in which the copies are located on each of the long arms of the homoeologous group 1 chromosomes. Screening of a variety of genotypes additionally reveals a number of restriction fragment length polymorphisms associated with these loci. Screening of a library of genomic DNA cloned in the vector λEMBL 4 has resulted in the isolation of a genomic fragment containing two closely linked Em genes. These are separated by ca. 2.5 kb. Analysis of restriction enzyme digests of this clones fragment has identified it as originating from chromosome 1A.

Abscisic acid enhances the transcription of wheat-germ agglutinin mRNA without altering its tissue-specific expression

We used RNA gel-blot analysis, in-situ hybridization, and nuclear run-on transcription to examine the effects of exogenous abscisic acid (ABA) on the spatial distribution of mRNA for the lectin wheat-germ agglutinin (WGA) in developing wheat (Triticum aestivum L. cv. Marshall) embryos and seedlings. When analyzed by RNA gel blots, both developing embryos and seedlings exhibited higher steady-state levels of WGA mRNA after ABA treatment. As determined by in-situ hybridization, incubation of developing embryos in 0.1 mM ABA resulted in accumulation of WGA mRNA in the epidermal and subepidermal cell layers of the radicle and seminal roots and throughout the rootcap and coleorhiza. This spatial distribution was identical to that in control embryos. Nuclear run-on transcription assays indicated that at least part of this increase is attributable to transcriptional induction. Thus, exogenous ABA is capable of inducing increased WGA mRNA accumulation only in cells where it is expressed during normal embryogenesis. When seeds were germinated in the absence of ABA, WGA mRNA was detected only in the rootcap. In contrast, seeds imbibed and germinated in the presence of ABA for 3 d exhibited a spatial distribution of WGA mRNA similar to that observed in developing embryos treated with ABA. In contrast, when ABA was added to 3-d-old seedlings, WGA mRNA was not detected in regions of the root beyond the rootcap. We conclude that exogenous ABA, when applied continuously from imbibition, causes retention of the embryo-specific pattern of WGA mRNA distribution and that the spatial pattern of WGA mRNA expression in roots does not change when ABA is added after germination.

Molecular analysis of a phylogenetically conserved carrot gene: developmental and environmental regulation

Extensive studies of gene expression programs in carrot somatic embryos identified a gene, designated Dc3, that serves as a reliable molecular marker for the acquisition of embryogenic potential by carrot cells in culture. The complete sequence of a carrot genomic region, DcG3, encoding a Dc3-like mRNA, was determined. The DcG3 transcription unit contains a single intron and encodes mRNA that is expressed at high levels in embryonic tissue but is undetectable in somatic tissue of carrot. The predicted protein sequence of DcG3 is 163 amino acids and includes two approximately 50 amino acid direct repeats which in turn include additional repetitive elements with an unusual distribution of charged amino acids. Dc3 and Dc3-like mRNAs are encoded by a small divergent gene family. Furthermore, similarities of the Dc3 gene family with genes from other plant species that are expressed in response to environmental and developmental cues suggest a possible role in seed desiccation and possibly in more general water-stress responses in plants. Analysis of transgenic tobacco containing a beta-glucuronidase (GUS) reporter gene fused to a 1.7 kb 5' upstream element of DcG3 defined a promoter/enhancer complex that confers developmentally and environmentally regulated expression of GUS activity. Thus, DcG3 is phylogenetically conserved together with the trans-acting factors required for its regulated expression in transgenic tobacco.

Abscisic acid: a role in shoot enhancement from loblolly pine (Pinus taeda L.) cotyledon explants

Enhancement of shoot regeneration from loblolly pine (Pinus taeda L.) cotyledon explants was studied by addition of abscisic acid (ABA) to Gresshoff-Doy (GD) shoot induction medium containing benzylaminopurine (BA) and naphthaleneacetic acid (NAA). Addition of ABA (10(-7) M) doubled the morphogenic area of cotyledons and increased the fresh weight of cotyledon explants by 40 to 45% after 4 weeks. A 4-week exposure to ABA resulted in a larger morphogenic area per cotyledon than 3, 2, or 1 week(s) respectively. The enhancement by ABA was related to the explant seed source and was not increased by prolonged exposure. Compared to controls, shoot number was enhanced by 31% and 56% with 2 and 4 weeks of ABA (10(-7) M) exposure, respectively. Abscisic acid has a role in enhancing shoot morphogenesis in loblolly pine.

Unusual sequence of an abscisic acid-inducible mRNA which accumulates late in Brassica napus seed development

We have analyzed the nucleotide sequence and accumulation of an mRNA which is prevalent in seeds of Brassica napus L. During normal development, the mRNA begins to accumulate during late embryogeny, is stored in dry seeds, and becomes undetectable in seedlings within 24 hours after imbibition. Moreover, abscisic acid treatment of embryos precociously induces or enhances accumulation of the mRNA. Nucleotide sequencing studies show that the deduced 30 kDa polypeptide has an unusual primary structure; the polypeptide possesses direct amino acid sequence repeats and is virtually entirely hydrophilic with the exception of a hydrophobic carboxyl-terminal region. Based upon the expression pattern and predicted polypeptide sequence, we conclude that the mRNA is encoded by a late embryogenesis-abundant (Lea) gene in B. napus.