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PubMed1989

The amyloplast-targeting transit peptide of the waxy protein of maize also mediates protein transport in vitro into chloroplasts.

The transit peptide of the waxy protein of maize which in the maize plant targets this protein only into amyloplasts was used for in vitro protein transport experiments with isolated amyloplasts from maize and chloroplasts from maize, pea and potato. In the presence of both intact and disrupted amyloplasts an artificial preprotein (TP30), consisting of the waxy transit peptide plus the first 34 amino acids of the mature waxy protein fused in-frame to the beta-glucuronidase of Escherichia coli, is processed to the size expected when the transit peptide is cleaved off. The chloroplasts studied show in vitro import and correct processing of both TP30 and the authentic waxy protein, but not of the beta-glucuronidase without the waxy transit peptide. The in vitro import of TP30 into chloroplasts is almost as efficient as that of the precursor of the small subunit of pea ribulose-1,5-bisphosphate carboxylase, a nuclear-encoded chloroplast protein, whereas the waxy protein accumulates to a lesser extent in the chloroplasts. Since the amino-terminal transit peptides of TP30 and the waxy precursor are the same, this difference must be due to the mature part of the waxy protein. One possible explanation is the observed instability of the waxy protein in the presence of chloroplasts.

Amino Acid Sequence↗

PubMed1989

The maize En-1/Spm element transposes in potato.

The maize transposable element En-1 has been introduced into a diploid potato line via transformation with Agrobacterium tumefaciens. The element is transcriptionally active in potato. Numerous En specific RNAs are observed, including a 6 kb transcript characteristic of an active En-1 element in maize. In contrast to maize, where the 6.0 kb transcript is hardly detectable, this transcript is very abundant in the transgenic potato. Transposition of En-1 in the potato clone was analysed by Southern blot hybridization and confirmed by molecular isolation of En-1 excision and integration events. Sequence data of excision and integration sites revealed footprints and target site duplications similar to the ones described for En-1 in maize.

Blotting, Southern↗

PubMed1988

Differential expression of a gene for a methionine-rich storage protein in maize.

A methionine-rich 10 kDa zein storage protein from maize was isolated and the sequence of the N-terminal 30 amino acids was determined. Based on the amino acid sequence, two mixed oligonucleotides were synthesized and used to probe a maize endosperm cDNA library. A full-length cDNA clone encoding the 10 kDa zein was isolated by this procedure. The nucleotide sequence of the cDNA clone predicts a polypeptide of 129 amino acids, preceded by a signal peptide of 21 amino acids. The predicted polypeptide is unique in its extremely high content of methionine (22.5%). The maize inbred line BSSS-53, which has increased seed methionine due to overproduction of this protein, was compared to W23, a standard inbred line. Northern blot analysis showed that the relative RNA levels for the 10 kDa zein were enhanced in developing seeds of BSSS-53, providing a molecular basis for the overproduction of the protein. Southern blot analysis indicated that there are one or two 10 kDa zein genes in the maize genome.

Amino Acid Sequence↗

PubMed1989

Identification in maize mitochondrial 26S rRNA of a short 5'-end sequence possibly involved in transcription initiation and processing.

By direct RNA mapping, we have identified the precise 5' end of the maize mitochondrial 26S rRNA. The 5' termini of the 26S rRNA are 17 and 18 nt downstream from the 5' end predicted by Dale et al. (1984) from homology between the maize rRNA and E. coli large subunit ribosomal RNA. In addition, we have discovered a larger 26S species, presumably a 26S precursor, and precisely mapped its 5' end. The maize mitochondrial rRNA genes are probably regulated by control regions that differ from those already characterized in other genomes: the maize mitochondrial 26S, 18S and 5S rRNAs lack sequences that resemble the promoter regions of genes from other mitochondria and bacteria. However, the mature and precursor rRNAs all contain a tetranucleotide, AAUC, at their 5' ends (AAAC in the 5S rRNA). The sequence is also seen in the same position in several other plant mitochondrial mRNAs. We propose therefore that AAUC is a transcription or processing signal which is possibly unique to plant mitochondria.

Base Sequence↗

PubMed1980

In vitro translation of maize ADH: evidence for the anaerobic induction of mRNA.

Total cellular RNA from anaerobically stressed maize seedling roots was used to stimulate in vitro translation of authentic maize alcohol dehydrogenase (ADH) in a rabbit reticulocyte lysate system. Total products from such reactions were displayed on NEPHGE-SDS two-dimensional gels and the Adhl-specific translation products were identified by using RNA from sib seedlings segregating for Adhl charge and size variants. The application of a rapid RNA isolation procedure allowed the efficient isolation of biologically active RNAs from small amonts of seedling material. Maize ADHs translated in vitro are identical in size to in vivo ADH. Further, no ADH was detected in the products of an in vitro translation reaction stimulated by total RNA from aerobically grown seedlings. This suggests that induction of ADH protein by anaerobic stress is accomplished by production of Adh mRNA rather than activation of sequestered mRNA. The mRNAs for maize ADH1 and ADH2 are among a small class of mRNAs induced during anaerobiosis.

Alcohol Oxidoreductases↗

PubMed1994

Chemical composition and functional properties of blends of maize and bambara groundnut flours for cookie production.

Chemical composition and functional properties of flour blends containing various levels of maize (100-0%) and bambara groundnut (0-100%) were studied. The resultant blends were high in protein, carbohydrate and caloric value. The blends contained fair amounts of Ca, P and K but were low in Na and Fe. The oil and water absorption capacities of the blends were fairly high ranging from 3.65 to 3.81 g oil/g sample and 3.40 to 3.80 g water/g sample, respectively. The gelation concentration of the blends tended to increase with increase in amount of maize flour in the blend. On the other hand, increasing the level of maize flour in the blends considerably reduced the foaming capacities of the blends. The flour blends had good emulsifying properties. Cookies prepared from the blends contained proteins ranging from 10.9 to 21.65% The cookies had good spread and were significantly lighter than the wheat control cookies. Sensory evaluation scores for cookies showed that the best level of combination was 75% maize flour and 25% bambara groundnut flour.

Arachis↗

PubMed2001

Inhibition of trans-membrane hexacyanoferrate III reductase activity and proton secretion of maize (Zea mays L.) roots by thenoyltrifluoroacetone.

Intact plants can reduce external oxidants by an appearingly trans-membrane electron transport. In vivo an increase in net medium acidification accompanies the reduction of the apoplastic substrate. Up to now, several NAD(P)H dehydrogenases, b-type cytochromes, and a phylloquinone have been identified and partially purified from plant plasma membranes. The occurrence of a quinone in the plasma membrane of maize roots supports the hypothetical model of a proton-transferring redox system, i.e., an electron transport chain with a quinone as mobile electron and proton carrier. In the present study the trans-membrane electron transport system of intact maize (Zea mays L.) roots was investigated. Flow-through and ionostat systems have been used to estimate the electron and proton transport activity of this material. Application of 4,4,4-trifluoro-1-(2-thienyl)-butane-1,3-dione (thenoyltrifluoroacetone) inhibited the reduction of ferricyanide in the incubation solution of intact maize roots up to 70%. This inhibition could not be washed off by rinsing the roots with fresh incubation medium. The acidification of the medium induced after ferricyanide application was inhibited to about 62%. The effects of thenoyltrifluoroacetone on proton fluxes in the absence of ferricyanide have been characterized in a pH-stat system. The net medium acidification by maize roots was inhibited up to 75% by thenoyltrifluoroacetone in the absence of ferricyanide, while dicumarol inhibited net acidification completely. The inhibition of H(+)-ATPase activity was estimated with plasma membrane vesicles isolated by phase partitioning and treated with 0.05% (w/v) Brij 58. ATP-dependent proton gradients and Pi release were measured after preincubation with the effectors. The proton pumping activity by those plasma membrane vesicles was inhibited by dicumarol (53.6%) and thenoyltrifluoroacctone (77.8%), while the release of Pi was unaffected by both inhibitors.

Cell Membrane↗

PubMed2001

Interaction between electron transport at the plasma membrane and nitrate uptake by maize (Zea mays L.) roots.

In the present study nitrate uptake by maize (Zea mays L.) roots was investigated in the presence or absence of ferricyanide (hexacyanoferrate III) or dicumarol. Nitrate uptake caused an alkalization of the medium. Nitrate uptake of intact maize seedlings was inhibited by ferricyanide while the effect of dicumarol was not very pronounced. Nitrite was not detected in the incubation medium, neither with dicumarol-treated nor with control plants after application of 100 microM nitrate to the incubation solution. In a second set of experiments interactions between nitrate and ferricyanide were investigated in vivo and in vitro. Nitrate (1 or 3 mM) did neither influence ferricyanide reductase activity of intact maize roots nor NADH-ferricyanide oxidoreductase activity of isolated plasma membranes. Nitrate reductase activity of plasma-membrane-enriched fractions was slightly stimulated by 25 microM dicumarol but was not altered by 100 microM dicumarol, while NADH-ferricyanide oxidoreductase activity was inhibited in the presence of dicumarol. These data suggest that plasma-membrane-bound standard-ferricyanide reductase and nitrate reductase activities of maize roots may be different. A possible regulation of nitrate uptake by plasmalemma redox activity, as proposed by other groups, is discussed.

Biological Transport↗

PubMed1987

The Ds1 controlling element family in maize and Tripsacum.

Hybridization experiments indicated that the maize genome contains a family of sequences closely related to the Ds1 element originally characterized from the Adh1-Fm335 allele of maize. Examples of these Ds1-related segments were cloned and sequenced. They also had the structural properties of mobile genetic elements, i.e., similar length and internal sequence homology with Ds1, 10- or 11-bp terminal inverted repeats, and characteristic duplications of flanking genomic DNA. All sequences with 11-bp terminal inverted repeats were flanked by 8-bp duplications, but the duplication flanking one sequence with 10-bp inverted repeats was only 6 bp. Similar Ds1-related sequences were cloned from Tripsacum dactyloides. They showed no more divergence from the maize sequences than the individual maize sequences showed when compared with each other. No consensus sequence was evident for the sites at which these sequences had inserted in genomic DNA.

Base Sequence↗

PubMed1984

Zein gene organization in maize and related grasses.

Zein cDNA clones were used to study the organization of zein genes within the genome of the inbred maize W64A. When individual clones for the two larger molecular-weight classes of zein proteins (Mr = 22,000; Mr = 19,000) were used as probes for Southern blot hybridizations of genomic DNA, multiple restriction fragments were found to hybridize. Reconstruction analyses using moderately stringent criteria were used to estimate a total of 70-80 zein sequences within the genome of this inbred maize. The hybridization patterns suggest that zein sequences are clustered within the same restriction fragment. When criteria permitting less cross-hybridization of homologous sequences (Tm - 10 degrees C) were used, the banding pattern changed, with some of the bands being reduced in intensity or eliminated entirely. Therefore, by control of hybridization criteria, particular zein genes may be more readily distinguished in a Southern blot analysis. The Southern blot hybridization pattern for the Mr = 15,000 zein was less complex. Only a single major band was found, with sufficient hybridization intensity for two or three genes. Genomic Southern analyses of other inbred maizes and related grasses showed similarly complex hybridization patterns with cDNA probes for the 19,000- and 22,000-molecular-weight zeins, suggesting that these sequences have been conserved over evolutionary time. The zein multigene family may therefore have arisen by gene duplication before divergence of the maize, teosinte, and Tripsacum species from a common ancestor.

Cloning, Molecular↗

PubMed1996

The transcriptional activator Opaque-2 controls the expression of a cytosolic form of pyruvate orthophosphate dikinase-1 in maize endosperms.

The maize Opaque-2 (O2) protein is a transcription factor of the basic/leucine-zipper class, involved in the regulation of endosperm proteins including the 22kDa alpha-zein storage proteins and b32 protein. In this study we have focussed our attention on the relationship between O2 and the cyPPDK1 gene, which encodes a cytoplasmic pyruvate orthophosphate dikinase (PPDK) isoform. The results of this study showed that PPDK activity is detectable in wild-type maize endosperms, while in o2 mutant endosperms, the levels of PPDK protein, mRNA and enzymatic activity are reduced, indicating that O2 is involved in the regulation of cyPPDK1 in this tissue. By employing transient expression experiments in tobacco mesophyll protoplasts, we have demonstrated that the O2 protein can activate expression of a chloramphenicol acetyl transferase reporter gene placed under the control of the cyPPDK1 promoter. An in vitro binding assay and DNaseI footprint analysis demonstrated that a specific sequence in the cyPPDK1 promoter can be recognized and protected by maize O2 protein. The regulation by the O2 locus of cyPPDK1 reported here, and control of alpha-zein synthesis by O2 suggest that the O2 protein may play a more general role in maize endosperm development than previously thought.

Base Sequence↗

PubMed1996

Molecular analysis of the structure of the maize B-chromosome.

The overall composition of the maize B is similar to that of the standard chromosome complement (A-chromosomes). This has been demonstrated by the use of several methods including: (a) genomic in situ hybridization (GISH), (b) analysis of highly repetitive sequences by the comparison of restriction digests of 0B and +B DNA and (c) the characterization of middle-repetitive cloned sequences. By the use of the technique of random amplification of polymorphic DNA-polymerase chain reaction, we have identified a B-specific repetitive sequence family. Sequence analysis of the B-specific clone reveals a relationship to the PREM-1 family of maize retroelements, which are preferentially transcribed in pollen. These results suggest an internal origin of the B-chromosome from within the maize genome, but demonstrate also that specific sequences can evolve by rapid processes of genomic turnover. Models for the origin of the maize B are discussed in the context of the present data.

Base Sequence↗

PubMed1996

Molecular evolution of maize catalases and their relationship to other eukaryotic and prokaryotic catalases.

We have compared the nucleotide and protein sequences of the three maize catalase genes with other plant catalases to reconstruct the evolutionary relationship among these catalases. These sequences were also compared with other eukaryotic and prokaryotic catalases. Phylogenies based on distances and parsimony analysis show that all plant catalases derive from a common ancestral catalase gene and can be divided into three distinct groups. The first, and major, group includes maize Cat1, barley Cat1, rice CatB, and most of the dicot catalases. The second group is an apparent dicot-specific catalase group encompassing the tobacco Cat2 and tomato Cat. The third is a monocot-specific catalase class including the maize Cat3, barley Cat2, and rice CatA. The maize Cat2 gene is loosely related to the first group. The distinctive features of monocot-specific catalases are their extreme high codon bias at the third position and low degree of sequence similarity to other plant catalases. Similarities in the intron positions for several plant catalase genes support the conclusion of derivation from a common ancestral gene. The similar intron position between bean catalases and human catalase implies that the animal and plant catalases might have derived from a common progenitor gene sequence.

Catalase↗

PubMed1988

New isozyme systems for maize (Zea mays L.): aconitate hydratase, adenylate kinase, NADH dehydrogenase, and shikimate dehydrogenase.

Electrophoretic variation and inheritance of four novel enzyme systems were studied in maize (Zea mays L.). A minimum of 10 genetic loci collectively encodes isozymes of aconitate hydratase (ACO; EC 4.2.1.3.), adenylate kinase (ADK; EC 2.7.4.3), NADH dehydrogenase (DIA; EC 1.6.99.-), and shikimate dehydrogenase (SAD; EC 1.1.1.25). At least four loci are responsible for the genetic control of ACO. Genetic data for two of the encoding loci, Aco1 and Aco4, demonstrated that at least two maize ACOs are active as monomers. Analysis of organellar preparations suggests that ACO1 and ACO4 are localized in the cytosolic and mitochondrial subcellular fractions, respectively. Maize ADK is encoded by a single nuclear locus, Adk1, governing monomeric enzymes that are located in the chloroplasts. Two cytosolic and two mitochondrial forms of DIA were electrophoretically resolved. Segregation analyses demonstrated that the two cytosolic isozymes are controlled by separate loci, Dia1 and Dia2, coding for products that are functional as monomers (DIA1) and dimers (DIA2). The major isozyme of SAD is apparently cytosolic, although an additional faintly staining plastid form may be present. Alleles at Sad1 are each associated with two bands that cosegregate in controlled crosses. Linkage analyses and crosses with B-A translocation stocks were effective in determining the map locations of six loci, including the previously described but unmapped locus Acp4. Several of these loci were localized to sparsely mapped regions of the genome. Dia2 and Acp4 were placed on the distal portion of the long arm of chromosome 1, 12.6 map units apart. Dia1 was localized to chromosome 2, 22.2 centimorgans (cM) from B1. Aco1 was mapped to chromosome 4, 6.2 cM from su1. Adk1 was placed on the poorly marked short arm of chromosome 6, 8.1 map units from rgd1. Less than 1% recombination was observed between Glu1 (on chromosome 10) and Sad1. In contrast to many other maize isozyme systems, there was little evidence of gene duplication or of parallel linkage relationships for these allozyme loci.

Aconitate Hydratase↗

PubMed1995

A maize DNA-binding factor with a bZIP motif is induced by low temperature.

We have isolated a low temperature-induced maize gene, mlip15, via cross hybridization using rice lip19. The longest cDNA isolated comprised 1179 bp and coded for a 135 amino acid bZIP (basic region/leucine zipper) protein. The gene showed 61.4% and 68.9% identity with the rice gene at the DNA and amino acid sequence levels, respectively, and is distinct from other maize genes that code for bZIP proteins. The level of mlip15 transcript was positively regulated by low temperature in the same way as the lip19 transcript. The levels of the transcript were also strongly increased by salt stress and exogenous abscisic acid, and slightly increased by anaerobiosis, but were not affected by heat shock and drought. The mLIP15 protein and truncated derivatives, produced in rabbit reticulocyte lysates or in an Escherichia coli expression system, were able to bind to a fragment of the wheat histone H3 gene promoter. This binding was diminished by addition of a molar excess of the hexamer sequence 5'-ACGTCA-3' found in the promoter and of the G-box-like sequence, but not by the addition of the ocs sequence or a mutated hexamer sequence. The factor bound to a promoter region of the maize Adh1 gene, expression of which is also induced by low temperature. These results lead to the conclusion that mlip15 is a strong candidate for a low temperature-induced transcription factor in maize.

Amino Acid Sequence↗

PubMed1995

The binding motifs for Ac transposase are absolutely required for excision of Ds1 in maize.

A reverse genetic system for studying excision of the transposable element Ds1 in maize plants has been established previously. In this system, the Ds1 element, as part of the genome of maize streak virus (MSV), is introduced into maize plants via agroinfection. In the presence of the Ac element, excision of Ds1 from the MSV genome results in the appearance of viral symptoms on the maize plants. Here, we used this system to study DNA sequences required in cis for excision of Ds1. The Ds1 element contains the Ac transposase binding motif AAACGG in only one of its subterminal regions (defined here as the 5' subterminal region). We showed that mutation of these motifs abolished completely the excision capacity of Ds1. This is the first direct demonstration that the transposase binding motifs are essential for excision. Mutagenesis with oligonucleotide insertions in the other (3') subterminal region resulted in elements with either a reduced or an increased excision efficiency, indicating that this subterminal region also has an important function.

Base Sequence↗

PubMed1989

Strong functional GC pressure in a light-regulated maize gene encoding subunit GAPA of chloroplast glyceraldehyde-3-phosphate dehydrogenase: implications for the evolution of GAPA pseudogenes.

The light-regulated nuclear gene encoding subunit A of chloroplast glyceraldehyde-3-phosphate dehydrogenase (subunit GAPA, gene Gpa1) from maize is extremely G + C rich (67% in codons). The genomic surroundings of this gene have been characterized together with the sequences of two strongly conserved Gpa pseudogenes isolated from a genomic maize library by differential cDNA hybridization. The comparisons show that the high G + C content of the maize gene is maintained independently of the surrounding noncoding sequences, which are G + C poor (42%), and only as long as the gene encodes a functional protein. After nonfunctionalization, Gpa pseudogenes rapidly loose G + C mainly due to enhanced turnover of CpG and CpXpG methylation sites. These results suggest that the maize Gpa1 gene is under strong functional GC pressure, due to constraints (CpG island) probably exerted at the transcriptional level. They also indicate that Gpa pseudogenes are methylated and that methylation was either the cause or the immediate consequence of their nonfunctionalization. It can be concluded further that the progenitor of pseudogenes 1 and 2 was a second functional Gpa gene (Gpa'), which, after duplication, accelerated in evolutionary rate due to relaxation of selective constraints. This is in agreement with the neutral theory of evolution. Comparison of Gpa intron sequences reveals a gradient of divergence: the more 3' the position of an intron the more its sequence has diverged between the three Gpa genes. A speculative model is presented explaining these observations in terms of a homologous recombination of genes with their reverse-transcribed pre-mRNAs.

Amino Acid Sequence↗

PubMed2005

Enhancement of resistance to aphids by introducing the snowdrop lectin gene gna into maize plants.

In order to enhance the resistance to pests, transgenic maize (Zea mays L.) plants from elite inbred lines containing the gene encoding snowdrop lectin (Galanthus nivalis L. agglutinin; GNA) under control of a phloem-specific promoter were generated through the Agrobacterium tumefaciens-mediated method. The toxicity of GNA-expressing plants to aphids has also been studied. The independently derived plants were subjected to molecular analyses. Polymerase chain reaction (PCR) and Southern blot analyses confirmed that the gna gene was integrated into maize genome and inherited to the following generations. The typical Mendelian patterns of inheritance occurred in most cases. The level of GNA expression at 0.13%-0.28% of total soluble protein was observed in different transgenic plants. The progeny of nine GNA-expressing independent transformants that were derived separately from the elite inbred lines DH4866, DH9942, and 8902, were selected for examination of resistance to aphids. These plants synthesized GNA at levels above 0.22% total soluble protein, and enhanced resistance to aphids was demonstrated by exposing the plants to corn leaf aphid (Rhopalosiphum maidis Fitch) under greenhouse conditions. The nymph production was significantly reduced by 46.9% on GNA-expressing plants. Field evaluation of the transgenic plants supported the results from the inoculation trial. After a series of artificial self-crosses, some homozygous transgenic maize lines expressing GNA were obtained. In the present study, we have obtained new insect-resistant maize material for further breeding work.

Agrobacterium tumefaciens↗