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PubMed2004

Patterns of population structure in maize landraces from the Central Valleys of Oaxaca in Mexico.

Assessing the impact of farmer management of maize landraces in the Central Valleys of Oaxaca, Mexico is crucial to an understanding of maize evolution, as it was first domesticated there. In this paper, we report on the impact of traditional farmer management of maize populations in this region in structuring molecular diversity and on the population dynamics of maize landraces. These populations, from a sample of local landraces cultivated by farmers in six villages, show little among-population differentiation (Fst=0.011). Most surprisingly, there is no isolation by distance and small among-village differentiation (Fst=0.003). For an outbreeding plant such as maize, one would expect populations to fit Hardy-Weinberg equilibrium, but significant homozygote excess (Fis=0.13) was found. This homozygote excess shows remarkable interpopulation and interlocus differences. We show that this pattern is related to variation in the mean anthesis-silking interval as well as to the flowering range or heterogeneity in flowering of a given population. A short anthesis-silking interval and high level of heterogeneity in flowering precocity will favor assortative mating. This leads to a locus-dependent population substructure giving an unusual case of Wahlund effect and inbreeding while high levels of seed exchange among farmers prevent population differentiation at both village and regional levels.

Agriculture↗

PubMed1968

Biosynthesis of phytoquinones. Biosynthetic origins of the nuclei and satellite methyl groups of plastoquinone, tocopherols and tocopherolquinones in maize shoots, bean shoots and ivy leaves.

1. By using dl-[ring-(14)C]phenylalanine, dl-[beta-(14)C]phenylalanine, dl-[alpha-(14)C]-tyrosine and dl-[beta-(14)C]tyrosine it was shown that in maize shoots (Zea mays) the nucleus and one nuclear methyl group of each of the following compounds, plastoquinone, gamma-tocopherol (aromatic nucleus) and alpha-tocopherolquinone, are formed from the nuclear carbon atoms and beta-carbon atom respectively of either exogenous phenylalanine or exogenous tyrosine. With ubiquinone only the aromatic ring of the amino acid is used in the synthesis of the quinone nucleus. Chemical degradation of plastoquinone and gamma-tocopherol molecules labelled from l-[U-(14)C]tyrosine established that a C(6)-C(1) unit directly derived from the amino acid is involved in the synthesis of these compounds. Radioactivity from [beta-(14)C]cinnamic acid is not incorporated into plastoquinone, tocopherols or tocopherolquinones, demonstrating that the C(6)-C(1) unit is not formed from any of the C(6)-C(1) phenolic acids associated with the metabolism of this compound. 2. The incorporation of radioactivity from l-[U-(14)C]tyrosine, dl-[beta-(14)C]tyrosine and dl-[U-(14)C]phenylalanine into bean shoots (Phaseolus vulgaris) and dl-[beta-(14)C]tyrosine and l-[Me-(14)C]methionine into ivy leaves (Hedera helix) was also investigated. Similar results were obtained to those reported for maize, except that in beans phenylalanine is only used for ubiquinone biosynthesis. This is attributed to the absence of phenylalanine hydroxylase from these tissues. In ivy leaves it is found that the beta-carbon atom of tyrosine gives rise to the 8-methyl group of delta-tocopherol, and it is suggested that for all other compounds examined it will give rise to the nuclear methyl group meta to the polyprenyl unit. 3. Preliminary investigations with the alga Euglena gracilis showed that in this organism ring-opening of tyrosine occurs to such an extent that the incorporation data from radiochemical experiments are meaningless. 4. The above results, coupled with previous observations, are interpreted as showing that in higher plants the nucleus of ubiquinone can be formed from either phenylalanine or tyrosine by a pathway involving as intermediates p-coumaric acid and p-hydroxybenzoic acid. Plastoquinone, tocopherols and alpha-tocopherolquinone are formed from p-hydroxyphenylpyruvate by a pathway in which the aromatic ring and C-3 of the side chain give rise respectively to the nucleus and to one nuclear methyl group. 5. Dilution experiments provided evidence that in maize shoots p-hydroxyphenylpyruvic acid and homogentisic acid (produced from p-hydroxyphenylpyruvic acid) are involved in plastoquinone biosynthesis, and presumably the biosynthesis of related compounds: however, other possible intermediates in the conversion including toluquinol (the aglycone of the proposed key intermediate) showed no dilution effects. Further, radioactivity from [Me-(14)C]toluquinol is not incorporated into any of the compounds examined. 6. Dilution experiments with 3,4-dihydroxybenzaldehyde and radioactive-labelling experiments with 3,4-dihydroxy[U-(14)C]benzoic acid demonstrated that these compounds are not involved in the biosynthesis of either ubiquinone or phylloquinone in maize shoots. 7. Evidence is also presented to show that in maize shoots ring-opening of the aromatic amino acids takes place. The suggestion is offered that this may take place via homogentisic acid, as in animals and some micro-organisms.

Amino Acids↗

PubMed2005

UDP-glucose dehydrogenases of maize: a role in cell wall pentose biosynthesis.

UDPGDH (UDP-D-glucose dehydrogenase) oxidizes UDP-Glc (UDP-D-glucose) to UDP-GlcA (UDP-D-glucuronate), the precursor of UDP-D-xylose and UDP-L-arabinose, major cell wall polysaccharide precursors. Maize (Zea mays L.) has at least two putative UDPGDH genes (A and B), according to sequence similarity to a soya bean UDPGDH gene. The predicted maize amino acid sequences have 95% similarity to that of soya bean. Maize mutants with a Mu-element insertion in UDPGDH-A or UDPGDH-B were isolated (udpgdh-A1 and udpgdh-B1 respectively) and studied for changes in wall polysaccharide biosynthesis. The udpgdh-A1 and udpgdh-B1 homozygotes showed no visible phenotype but exhibited 90 and 60-70% less UDPGDH activity respectively than wild-types in a radiochemical assay with 30 microM UDP-glucose. Ethanol dehydrogenase (ADH) activity varied independently of UDPGDH activity, supporting the hypothesis that ADH and UDPGDH activities are due to different enzymes in maize. When extracts from wild-types and udpgdh-A1 homozygotes were assayed with increasing concentrations of UDP-Glc, at least two isoforms of UDPGDH were detected, having K(m) values of approx. 380 and 950 microM for UDP-Glc. Leaf and stem non-cellulosic polysaccharides had lower Ara/Gal and Xyl/Gal ratios in udpgdh-A1 homozygotes than in wild-types, whereas udpgdh-B1 homozygotes exhibited more variability among individual plants, suggesting that UDPGDH-A activity has a more important role than UDPGDH-B in UDP-GlcA synthesis. The fact that mutation of a UDPGDH gene interferes with polysaccharide synthesis suggests a greater importance for the sugar nucleotide oxidation pathway than for the myo-inositol pathway in UDP-GlcA biosynthesis during post-germinative growth of maize.

Amino Acid Sequence↗

PubMed1995

Expression and characterization of maize ZBP14, a member of a new family of zinc-binding proteins.

A maize gene (Mz2-12), with a deduced amino acid sequence similar to that of a protein kinase C (PKC) inhibitor from bovine brain, has been expressed in Escherichia coli and the protein (ZBP14) purified to homogeneity. The bovine protein was originally identified by Walsh's group and named PKC inhibitor-1 (PKCI-1). The recombinant maize protein (ZBP14) shares characteristics of bovine PKCI-1: it has similar secondary structure, is dimeric, and has a similar affinity for zinc. However, the maize ZBP14 had very little activity as an inhibitor of mammalian brain PKC, thus precluding zinc sequestration as the mechanism of inhibition. The biological role for the maize protein in plant kinase regulation is therefore unclear. In the presence of both maize ZBP14 and 14-3-3 protein (which inhibits PKC in the absence of diacylglycerol), the effects on PKC appeared to be synergistic.

Animals↗

PubMed1997

Cloning and characterization of a cDNA encoding a maize seedling phytase.

During germination, maize seedlings express a phytase able to hydrolyse the large amount of phytin stored in the dry seed. Previous studies allowed purification and characterization of this enzyme as a homodimer of 38 kDa subunits [Laboure, Gagnon and Lescure, Biochem. J. (1993) 295, 413-419]. In the present work, an antibody against the purified maize phytase has been used to screen a maize seedling cDNA expression library. Several positive clones containing an insert of about 1400 bp were isolated. The nucleotide sequence of the insert of one of these clones has been established. This cDNA, called phy S11, was 1335 bp long and contained an open reading frame of 387 amino acids. The sequence of N-terminal residues (23 amino acids) of the purified phytase has been established. These residues are found at positions 19-41 of the amino acid sequence encoded by phy S11. This confirms that this cDNA codes for the maize phytase. The deduced amino acid sequence appears to be very different from those of published Aspergillus niger phytases; however, an homologous region of 33 amino acids was detected. This region of the fungal sequence contains the RHGxRxP consensus motif found in various high molecular mass acid phosphatases and believed to be the acceptor site for phosphate. Expression of the phy S11 cDNA in Escherichia coli allowed the production of the phytase subunit and its assembly to give a protein of the same size as the native phytase. The time course of phy S11 mRNA accumulation during germination showed that no transcript was present in dry seeds. The mRNA accumulated during the first day of germination, to reach a maximum after 2 days (radicle protrusion), and then decreased in young seedlings. Genomic Southern blot analyses suggest the existence of at least two genes and genetic mapping reveals two loci separated by 1 cM on chromosome 3 of maize. The cloning of this first cDNA coding for a plant phytase, will allow the isolation of the corresponding genes and the study of their regulation during germination.

6-Phytase↗

PubMed1999

The protective effects of high amylose maize (amylomaize) starch granules on the survival of Bifidobacterium spp. in the mouse intestinal tract.

The possibility of using high amylose maize starch granules as a delivery system for probiotic bacteria has been investigated using Bifidobacterium spp. LaftiTM 8B and LaftiTM 13B which were isolated from a healthy human. The Bifidobacterium cells were able to adhere to the amylomaize starch granules and were also able to hydrolyse the starch during growth. Initially, in vitro studies were carried out by studying the survival of strains Bifidobacterium LaftiTM 8B and LaftiTM 13B when exposed to pH 2.3, 3.5 and 6.5 as well as 0.03 and 0.05% w/v bile acids. Both strains were grown either in the absence or presence of high amylose maize starch granules, then mixed with the high amylose maize starch granules and exposed to acidic buffers or bile acid solutions. It was shown that growth in and the presence of high amylose maize starch granules led to enhanced survival of strains LaftiTM 8B and LaftiTM 13B. Subsequently, survival in vivo was monitored by measuring the faecal level of Bifidobacterium LaftiTM 8B after oral administration of the strain to mice. A sixfold better recovery of strain LaftiTM 8B from mice faeces after oral dosage was noted for cells grown in amylose-containing medium compared with controls. It was concluded that high amylose maize starch granules contributed to enhanced survival of Bifidobacterium sp. LaftiTM 8B and LaftiTM 13B.

Administration, Oral↗

PubMed1993

The profilin multigene family of maize: differential expression of three isoforms.

Profilin is a small (12-15 kDa) actin- and phospholipid-binding protein previously known only from studies on animals and lower eukaryotes but recently identified as a birch pollen allergen. Here we have identified and characterized three members of the profilin multigene family from the plant Zea mays. Two cDNAs isolated from a maize pollen library (ZmPRO 1 and ZmPRO 3) each have a single, large open reading frame encoding a putative polypeptide 131 amino acids long with a predicted molecular weight of approximately 14 kDa. A third maize pollen cDNA (ZmPRO 2) has two in-frame translation initiation codons. Use of the first ATG would result in a polypeptide 137 amino acids long with a molecular weight of 14.8 kDa. The three maize profilins are highly homologous to each other (> 90% nucleotide and amino acid sequence identity) as well as other plant profilins but show far less similarity (30-40% amino acid sequence identity) to animal and lower eukaryote profilins. Multiple sequence alignments indicate that only nine residues are shared by all eukaryotic profilins examined. However, limited comparisons reveal domains in the NH2 and COOH termini that have a high degree of similarity suggesting functional conservation. The maize gene family size is estimated to contain three to six members based on Southern blot experiments with gene-specific and coding region probes. Northern blot analysis demonstrates that the three maize profilin cDNAs characterized here are utilized in a tissue-specific manner and are anther or pollen specific.

Actins↗

PubMed1994

Expression of a maize proteinase inhibitor gene is induced in response to wounding and fungal infection: systemic wound-response of a monocot gene.

The isolation and characterization of cDNA and genomic clones encoding a proteinase inhibitor protein (MPI) in maize is reported. Accumulation of the MPI mRNA is induced in response to fungal infection in germinating maize embryos. The expression pattern of the MPI gene, in healthy and fungal infected maize tissues, was examined and compared with the expression pattern of a gene that codes for a pathogenesis-related protein (the PRms protein) from maize. These two genes are induced by fungal infection, however different signals trigger their activation. Accumulation of the proteinase inhibitor mRNA is more a consequence of the wound produced by the penetration and colonization of the host tissues by the pathogen, than the result of a direct molecular recognition of the pathogen by the plant, as is the case for the induction of the PRms gene. Wounding, or treatment with abscisic acid or methyl jasmonate, stimulate MPI mRNA accumulation, but not PRms mRNA accumulation. Local and systemic induction of the MPI gene expression in response to wounding occurs in maize plants. To the authors' knowledge, this is the first example of a gene from a monocotyledonous species that clearly shows a systemic wound response. The possible functional implications for the existence of different signal transduction pathways that simultaneously activate a battery of defense mechanisms against potential pathogens are discussed.

Abscisic Acid↗

PubMed1995

A characterization of the MADS-box gene family in maize.

Studies on distantly related dicot plant species have identified homeotic genes that specify floral meristem identity and determine the fate of floral organ primordia. Most of these genes belong to a family characterized by the presence of a structural motif, the MADS-box, which encodes a protein domain with DNA-binding properties. As part of an effort to understand how such genes may have been recruited during the evolution of flowers with different organ types such as those found in maize, two members of this gene family in maize, ZAG1 and ZAG2, have been characterized previously. Here, the isolation and characterization of four new members of this gene family, designated ZAP1, ZAG3, ZAG4 and ZAG5, are described and the genetic map position of these and 28 additional maize MADS-box genes is determined. The first new member of this family appears to be the Zea mays ortholog of the floral homeotic gene APETALA1 (AP1) and has been designated ZAP1. One of these genes, ZAG4, is unusual in that its deduced protein sequence includes the MADS domain but lacks the K-domain characteristically present in this family of genes. In addition, its copy number and expression varies among different inbreds. A large number of maize MADS-box genes map to duplicated regions of the genome, including one pair characterized here, ZAG3 and ZAG5. These data underscore the complexity of this gene family in maize, and provide the basis for further studies into the regulation of floral organ morphogenesis among the grasses.

Amino Acid Sequence↗

PubMed1996

Metabolic regulation of asparagine synthetase gene expression in maize (Zea mays L.) root tips.

Differential hybridization of a cDNA library constructed with poly(A)+ mRNA from 24 h starved maize (Zea mays L.) root tips, resulted in the isolation of a cDNA (called pZSS1) that was highly induced during glucose deprivation. The nucleotide sequence analysis of the full-length cDNA allowed its identification by comparison with sequence data bases. The 586 amino acid sequence encoded by pZSS1 was shown to be about 60% identical to sequences of asparagine synthetases (EC 6.3.5.4) from Asparagus officinalis, Pisum sativum, Arabidopsis thaliana and Brassica oleracea. Southern blot analysis of maize genomic DNA showed that asparagine synthetase may be encoded by at least two genes. The use of a specific probe for the 3' untranslated region of pZSS1 in Northern blot experiments, revealed that the isolated AS gene was essentially expressed in roots of maize seedlings. Time course analysis revealed that maximal expression of the gene corresponding to pZSS1 occurs between 18 and 24 h after the onset of the starvation treatment. The steady-state levels of transcripts in maize root tips were found to change under various incubation conditions. Exogenous supply of metabolizable sugars downregulated the gene expression, while carbohydrate deprivation or feeding with non-metabolizable sugars resulted in the induction of gene expression. In addition to carbohydrate deprivation, the effects of nitrogen metabolite supply and stress conditions indicate that gene expression might be under metabolic control in maize root tips. The intracellular nitrogen to carbon ratio might be an important factor for the regulation of asparagine synthetase gene expression.

Amino Acid Sequence↗

PubMed2000

Tonoplast subcellular localization of maize cytochrome b5 reductases.

Plant cytochrome b5 reductases (b5R) are assumed to be part of an ER-associated redox chain that oxidizes NADH to provide electrons via cytochrome b5 (cyt b5) to ER-associated fatty acyl desaturase and related hydroxylases, as in mammalian cells. Here we report on cDNA cloning of a novel maize b5R, NFR II, strongly related to a previously cloned cDNA, NFR I (Bagnaresi et al., 1999, Biochem. J. 338, 499-505). Maize b5R isoforms are produced by a small multi-gene family. The NFR cDNAs were shown to encode active b5Rs by heterologous expression in yeast. Both reductases, in addition to Fe3+-chelates, efficiently reduced Cu2+-chelates. Using a polyclonal antibody able to recognize both NFR I and NFR II isoforms, no ER or mitochondrial localization could be detected in maize roots. Unexpectedly, maize b5Rs were found to be targeted to the tonoplast. Using the most specific assay to measure NFR activity, we confirmed that the highest NFR specific activity is associated with tonoplast-enriched maize root fractions. Tonoplast targeting is not consistent with a role in desaturase reactions or with the other functions ascribed to date to plant b5R. This indicates that alternative ER-associated electron donors for desaturases need to be sought, and that plant b5Rs may have previously unexpected functions.

Amino Acid Sequence↗

PubMed2001

Maize protein kinase CK2: regulation and functionality of three beta regulatory subunits.

Biochemical and crystallographic data suggest that, in contrast with other organisms, the active maize protein kinase CK2 might be composed simply of a catalytic polypeptide (CK2alpha), thus lacking CK2beta regulatory subunits. To investigate the existence and functionality of CK2beta regulatory subunits in Zea mays, we have screened a maize cDNA library using different approaches and have isolated three full-length cDNAs encoding CK2beta regulatory subunits (CK2beta-1, CK2beta-2 and CK2beta-3) and a cDNA coding for a novel CK2alpha catalytic subunit, CK2alpha-3. The pattern of expression of all these alpha/beta subunits has been studied in different organs and developmental stages using specific probes for each isoform, and indicates that while CK2alpha subunits are constitutive, CK2beta subunits are expressed differentially during embryo development. The yeast two-hybrid system and pull-down assays have been used to study specific interactions between the different subunits. While CK2alpha subunits are unable to self-associate, preferential interactions between alpha/beta isoforms and beta/beta isoforms can be predicted. Furthermore, we show that maize CK2alpha/beta subunits assemble into a structural tetrameric complex which has very similar properties to those described in other organisms, and that expression of maize CK2beta subunits in yeast allows the rescue of the phenotypic defects associated to the lack of CK2 function, thus demonstrating the functionality of maize CK2beta regulatory subunits.

Amino Acid Sequence↗

PubMed2002

Aspergillus section Flavi populations from field maize in Argentina.

AIMS: Populations of Aspergillus section Flavi were studied from a commercial field of maize in Río Cuarto, Córdoba, Argentina. METHODS AND RESULTS: The Aspergillus species were isolated from soil, debris and insects during three periods: pre-planting, growing maize and post-harvest. The colony count from non-rhizospheric soil in the pre-planting period was higher than in growing maize and the post-harvest period. Debris samples analysed during all periods showed similar infection percentages for Aspergillus section Flavi. The samples of insects collected during the maize-growing period showed a lower percentage of Aspergillus isolates than the samples from soil and debris. Aflatoxigenic strains were present in lower levels in each component of the agroecosystem studied. All the strains that produced sclerotia were L strains. CONCLUSIONS: In this field agroecosystem, the only strains with a high probability for transfer to the storage agroecosystem were L strains with low toxigenic potential. SIGNIFICANCE AND IMPACT OF THE STUDY: Maize pre-harvest contamination with aflatoxigenic inoculum was not significant.

Aflatoxins↗

PubMedDate not supplied

Monitoring the impact of Bt maize on butterflies in the field: estimation of required sample sizes.

The monitoring of genetically modified organisms (GMOs) after deliberate release is important in order to assess and evaluate possible environmental effects. Concerns have been raised that the transgenic crop, Bt maize, may affect butterflies occurring in field margins. Therefore, a monitoring of butterflies was suggested accompanying the commercial cultivation of Bt maize. In this study, baseline data on the butterfly species and their abundance in maize field margins is presented together with implications for butterfly monitoring. The study was conducted in Bavaria, South Germany, between 2000-2002. A total of 33 butterfly species was recorded in field margins. A small number of species dominated the community, and butterflies observed were mostly common species. Observation duration was the most important factor influencing the monitoring results. Field margin size affected the butterfly abundance, and habitat diversity had a tendency to influence species richness. Sample size and statistical power analyses indicated that a sample size in the range of 75 to 150 field margins for treatment (transgenic maize) and control (conventional maize) would detect (power of 80%) effects larger than 15% in species richness and the butterfly abundance pooled across species. However, a much higher number of field margins must be sampled in order to achieve a higher statistical power, to detect smaller effects, and to monitor single butterfly species.

Agriculture↗

PubMed2006

Detecting (trans)gene flow to landraces in centers of crop origin: lessons from the case of maize in Mexico.

There is much discussion of the probability of transgene flow from transgenic crop varieties to landraces and wild relatives in centers of origin or diversity, and its genetic, ecological, and social consequences. Without costly research on the variables determining gene flow, research on transgene frequencies in landrace (or wild relative) populations can be valuable for understanding transgene flow and its effects. Minimal research requirements include (1) understanding how farmer practices and seed systems affect landrace populations, (2) sampling to optimize Ne/n (effective/census population size), (3) minimizing variance at all levels sampled, and (4) using Ne to calculate binomial probabilities for transgene frequencies. A key case is maize in Mexico. Two peer-reviewed papers, based on landrace samples from the Sierra Juárez region of Oaxaca, Mexico, reached seemingly conflicting conclusions: transgenes are present (Quist and Chapela, 2001, Nature 414: 541-543; 2002, Nature 416: 602) or "detectable transgenes" are absent (Ortiz-García et al., 2005, Proc. Natl. Acad. Sci. USA 102: 12338-12343 and 18242). We analyzed these papers using information on Oaxacan maize seed systems and estimates of Ne. We conclude that if Quist and Chapela's results showing presence are accepted, Ortiz-García et al.'s conclusions of no evidence of transgenes at detectable levels or for their introgression into maize landraces in the Sierra de Juárez of Oaxaca are not scientifically justified. This is because their samples are not representative, and their statistical analysis is inconclusive due to using n instead of Ne. Using estimates of Ne based on Ortiz-García et al.'s n, we estimate that transgenes could be present in maize landraces in the Sierra Juárez region at frequencies of approximately 1-4%, and are more likely to be present in the 90% of Oaxacan landrace area that is not mountainous. Thus, we have no scientific evidence of maize transgene presence or absence in recent years in Mexico, Oaxaca State, or the Sierra Juárez region.

Crops, Agricultural↗

PubMedDate not supplied

Intestinal function and body growth of broiler chickens on diets based on maize dried at different temperatures and supplemented with a microbial enzyme.

A study was conducted to evaluate the effects of varying drying temperature (Fresh, 85, 95 or 105 degrees C) on the nutritive value of maize and response of broiler chickens to diets based on such grain, and supplemented with a microbial enzyme (Avizyme 1500). The chemical composition of the grain was affected by drying temperature. Starch and amylopectin contents were increased while there was a reduction in amylose content. These changes were expected to underlie the response of chicks to the diets. Total feed intake over 28 days was increased (P < 0.05) as a result of heat-treating the maize up to 95 degrees C. The final body weight of chicks on the diet based on fresh maize was improved (P < 0.05) by the microbial enzyme supplement (MES). There was no effect of the enzyme supplement on body weight when assessed at earlier ages. Over the entire feeding period, feed conversion efficiency (FCE) declined (P < 0.001) with increasing oven temperature, regardless of the supplementation with the microbial enzyme. Body weight was influenced (P < 0.05) by the microbial enzyme only when assessed over the entire trial period. The weight of visceral organs, protein content and activities of pancreatic and jejunal digestive enzymes were unaffected by grain heat treatment or MES. The ileal digestibility of calcium was reduced (P < 0.001) on diets based on fresh maize and maize that was oven-dried at 105 degrees C. Heat-treatment also improved (P < 0.05) the ileal digestibility of phosphorus in chicks on the diets without MES. There were no effects of grain heat treatment or MES on the ileal digestibility of energy, protein, Ca and amino acids. The results indicate some variations in grain quality as a result of heat treatment but the differences were not significant enough to stimulate major responses to the MES. Further studies should examine samples from commercial drying processes or samples obtained from a closer simulation of commercial conditions, to arrive at more practical conclusions.

Animal Feed↗

PubMed2002

The defective kernel 1 (dek1) gene required for aleurone cell development in the endosperm of maize grains encodes a membrane protein of the calpain gene superfamily.

Endosperm of cereal grains is one of the most important renewable resources for food, feed, and industrial raw material. It consists of four triploid cell types, i.e., aleurone, starchy endosperm, transfer cells, and cells of the embryo surrounding region. In maize, the aleurone layer is one cell layer thick and covers most of the perimeter of the endosperm. Specification of maize aleurone cell fate is proposed to occur through activation of the tumor necrosis factor receptor-like receptor kinase CRINKLY4. A second maize gene essential for aleurone cell development is defective kernel 1 (dek1). Here we show that DEK1 shares high homology with animal calpains. The predicted 2,159-aa DEK1 protein has 21 transmembrane regions, an extracellular loop, and a cysteine proteinase domain that shares high homology with domain II of m-calpain from animals. We propose that DEK1 functions to maintain and restrict the aleurone cell fate imposed by CR4 through activation of its cysteine proteinase by contact with the outer endosperm surface. DEK1 seems to be the only member of the calpain superfamily in plants, Arabidopsis DEK1 sharing 70% overall identity with maize DEK1. The expression of dek1 in most plant tissues in maize and Arabidopsis, as well as its presence in a variety of higher plants, including angiosperms and gymnosperms, suggests that DEK1 plays a conserved role in plant signal transduction.

Alleles↗

PubMed2005

A maize resistance gene functions against bacterial streak disease in rice.

Although cereal crops all belong to the grass family (Poacea), most of their diseases are specific to a particular species. Thus, a given cereal species is typically resistant to diseases of other grasses, and this nonhost resistance is generally stable. To determine the feasibility of transferring nonhost resistance genes (R genes) between distantly related grasses to control specific diseases, we identified a maize R gene that recognizes a rice pathogen, Xanthomonas oryzae pv. oryzicola, which causes bacterial streak disease. Bacterial streak is an important disease of rice in Asia, and no simply inherited sources of resistance have been identified in rice. Although X. o. pv. oryzicola does not cause disease on maize, we identified a maize gene, Rxo1, that conditions a resistance reaction to a diverse collection of pathogen strains. Surprisingly, Rxo1 also controls resistance to the unrelated pathogen Burkholderia andropogonis, which causes bacterial stripe of sorghum and maize. The same gene thus controls resistance reactions to both pathogens and nonpathogens of maize. Rxo1 has a nucleotide-binding site-leucine-rich repeat structure, similar to many previously identified R genes. Most importantly, Rxo1 functions after transfer as a transgene to rice, demonstrating the feasibility of nonhost R gene transfer between cereals and providing a valuable tool for controlling bacterial streak disease.

Amino Acid Sequence↗