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PubMed2005

Conservation and diversification of SCARECROW in maize.

The SCARECROW (SCR) gene in Arabidopsis is required for asymmetric cell divisions responsible for ground tissue formation in the root and shoot. Previously, we reported that Zea mays SCARECROW (ZmSCR) is the likely maize ortholog of SCR. Here we describe conserved and divergent aspects of ZmSCR. Its ability to complement the Arabidopsis scr mutant phenotype suggests conservation of function, yet its expression pattern during embryogenesis and in the shoot system indicates divergence. ZmSCR expression was detected early during embryogenesis and localized to the endodermal lineage in the root, showing a gradual regionalization of expression. Expression of ZmSCR appeared to be analogous to that of SCR during leaf formation. However, its absence from the maize shoot meristem and its early expression pattern during embryogenesis suggest a diversification of ZmSCR in the patterning processes in maize. To further investigate the evolutionary relationship of SCR and ZmSCR, we performed a phylogenetic analysis using Arabidopsis, rice and maize SCARECROW-LIKE genes (SCLs). We found SCL23 to be the most closely related to SCR in both eudicots and monocots, suggesting that a gene duplication resulting in SCR and SCL23 predates the divergence of dicots and monocots.

Arabidopsis↗

PubMed2006

Comparative structural and functional characterization of sorghum and maize duplications containing orthologous myb transcription regulators of 3-deoxyflavonoid biosynthesis.

Sequence characterization of the genomic region of sorghum yellow seed 1 shows the presence of two genes that are arranged in a head to tail orientation. The two duplicated gene copies, y1 and y2 are separated by a 9.084 kbp intergenic region, which is largely composed of highly repetitive sequences. The y1 is the functional copy, while the y2 may represent a pseudogene; there are several sequence indels and rearrangements within the putative coding region of y2. The y1 gene encodes a R2R3 type of Myb domain protein that regulates the expression of chalcone synthase, chalcone isomerase and dihydroflavonol reductase genes required for the biosynthesis of 3-deoxyflavonoids. Expression of y1 can be observed throughout the plant and it represents a combination of expression patterns produced by different alleles of the maize p1. Comparative sequence analysis within the coding regions and flanking sequences of y1, y2 and their maize and teosinte orthologs show local rearrangements and insertions that may have created modified regulatory regions. These micro-colinearity modifications possibly are responsible for differential patterns of expression in maize and sorghum floral and vegetative tissues. Phylogenetic analysis indicates that sorghum y1 and y2 sequences may have arisen by gene duplication mechanisms and represent an evolutionarily parallel event to the duplication of maize p2 and p1 genes.

Amino Acid Sequence↗

PubMed2006

A leaf-based regeneration and transformation system for maize (Zea mays L.).

Efficient methods for in vitro propagation, regeneration, and transformation of plants are of pivotal importance to both basic and applied research. While being the world's major food crops, cereals are among the most difficult-to-handle plants in tissue culture which severely limits genetic engineering approaches. In maize, immature zygotic embryos provide the predominantly used material for establishing regeneration-competent cell or callus cultures for genetic transformation experiments. The procedures involved are demanding, laborious and time consuming and depend on greenhouse facilities. We have developed a novel tissue culture and plant regeneration system that uses maize leaf tissue and thus is independent of zygotic embryos and greenhouse facilities. We report here: (i) a protocol for the efficient induction of regeneration-competent callus from maize leaves in the dark, (ii) a protocol for inducing highly regenerable callus in the light, and (iii) the use of leaf-derived callus for the generation of stably transformed maize plants.

DNA, Plant↗

PubMed1990

Glycan research on barley, maize, oats, and sorghum grain alpha-amylases: comparison with rice alpha-amylase.

alpha-Amylases from germinated maize, oats, rice, and sorghum were isolated by glycogen precipitation and hydrophobic interaction chromatography. Several methods were used for the detection of glycoproteins, including barley alpha-amylase isozymes purified as previously described and using the rice alpha-amylase as a positive control for glycosylation. Affinoblotting using concanavalin A, immunoblotting using a xylose-specific serum which reacts with complex N-linked glycans, and endo-beta-N-acetylglucosaminidase H treatment of amylases gave negative results for maize, oats, sorghum, and barley. However, after deglycosylation with trifluoromethanesulfonic acid, the molecular weight of one maize alpha-amylase constituent was clearly decreased. The same result was obtained after beta-elimination in mild conditions. Together these results indicated probable O-linked glycosylation of one maize alpha-amylase when barley, oats, and sorghum alpha-amylases did not appear to be glycosylated. Chemical deglycosylation of rice alpha-amylase resulted in the production of two polypeptides with different molecular weights.

Chromatography, Gel↗

PubMed1991

Illumination increases the phosphorylation state of maize leaf phosphoenolpyruvate carboxylase by causing an increase in the activity of a protein kinase.

Illumination of maize leaves increases the phosphorylation state of phosphoenolpyruvate carboxylase and reduces the sensitivity of the enzyme to feedback inhibition by malate. Red, white and blue light were each found to be equally potent, and the effect of light was blocked by 3(3,4-dichlorophenyl)-1,1-dimethylurea. A phosphoenolpyruvate carboxylase kinase was partially purified from illuminated maize leaves by a three-step procedure. Phosphorylation of phosphoenolpyruvate carboxylase by this protein kinase reached 0.7-0.8 molecules/subunit and correlated with a 3- to 4-fold increase in Ki for malate. The protein kinase was inhibited by L-malate, but was insensitive to a number of other potential regulators. Freshly prepared and desalted extracts of darkened maize leaves contained very little kinase activity, but the activity appeared when leaves were illuminated for 30-60 min before extraction. The catalytic subunit of protein phosphatase 2A from rabbit skeletal muscle, but not that of protein phosphatase 1, could dephosphorylate phosphoenolpyruvate carboxylase. The protein phosphatases 1 and 2A activities of maize leaves were not affected by illumination. It is suggested that the major means by which light stimulates the phosphorylation of phosphoenolpyruvate carboxylase is by an increase in the activity of the protein kinase.

Chromatography↗

PubMed1994

Significance of yeasts and moulds occurring in maize dough fermentation for 'kenkey' production.

Yeasts and moulds associated with the fermentation of maize dough during the processing of the West African traditional food 'kenkey' were investigated. A mixed flora comprising Candida, Saccharomyces, Trichosporon, Kluyveromyces and Debaryomyces species were isolated from raw maize, during steeping and early phases of fermentation. After 24-48 h of fermentation, Candida krusei and Saccharomyces cerevisiae dominated reaching counts exceeding 10(6) cfu/g. This succession of yeast populations and the significant multiplication of C. krusei and S. cerevisiae were observed in all cases for both the fermentation and the production sites investigated. Penicillium, Aspergillus and Fusarium species, including potential mycotoxin producers, were isolated from raw maize. Initial high counts of 10(5) cfu/g for moulds were reduced to less than 10(2)cfu/g within 24 h of fermentation. High levels of aflatoxins were observed in raw maize, and they were not affected during the fermentations.

Aflatoxins↗

PubMed1994

Physiological, biochemical and molecular processes associated with gravitropism in roots of maize.

This research aims to characterize regulation of the principal cytosolic protein kinases in maize, cultivar 'Merit' root tips, since much evidence indicates that stimuli which modulate the gravitropic response in this system act through regulation of activity of these enzymes. To this end, we have cloned a maize protein kinase belonging to a group of plant protein kinases with a catalytic domain similar in primary structure to the second messenger-regulated protein kinases known in animal and fungal systems. However, both the unique structural features conserved among plant protein kinases in this group, and lack of evidence for cyclic nucleotide signalling in plants point to operation of a novel protein kinase regulatory mechanism in plants. In order to test effects of possible regulators on protein kinase activity, we developed a sensitive method for detecting regulation of autophosphoryl labelling of protein kinases in unfractionated maize protein extracts. Regulation of protein kinase autophosphorylation in these extracts was different from that known in animals and fungi, further suggesting operation of unique protein kinase regulatory mechanisms in plants. Previous research has shown that light, or factors modulated by light, regulate plant protein kinase activity. We found that protein kinase activity was co-immunoprecipitated with the plant photoreceptor phytochrome, and was associated with phytochrome by high-affinity chemical interactions. Far-red reversibility of red-light regulation of phytochrome phosphorylation by the associated protein kinase indicates that it may modulate or transduce the light signals which lead to gravitropic sensitivity in 'Merit' maize.

Calcium↗

PubMed1986

Synthesis of maize chloroplast ATP-synthase beta-subunit fusion proteins in Escherichia coli and binding to the inner membrane.

The maize chloroplast gene for the beta subunit (atpB) of the chloroplast CF1 component of ATPase from maize, when fused to either the lacZ or ral genes in the vectors pMC1403 or pHUB4, is expressed in Escherichia coli as a fusion protein with beta-galactosidase or with bacteriophage lambda Ral sequences. Some of the fusion proteins are converted to a membrane-bound form, as determined by differential and sucrose-gradient centrifugation. The specificity of membrane binding has been examined using E. coli unc mutants that are defective in binding of the F1 ATPase component to the F0 receptor site on the membrane, and by the use of two different length maize atpB::lacZ gene fusions. We show that the first 365 N-terminal amino acids (aa) of the maize beta subunit are involved in binding to the E. coli inner membrane, and that this binding is probably mediated by the bacterial F0 receptor.

Cell Membrane↗

PubMed1989

Structure and expression of a maize phytochrome-encoding gene.

We have isolated genomic clones for three loci encoding the phytochrome polypeptide of Zea mays, and have determined the entire sequence of one of them (phyA1) together with approximately 1 kb of 5' flanking DNA. The structure of this gene is highly conserved in comparison with other phytochrome-encoding genes (phy). The deduced amino acid (aa) sequence indicates that the maize phytochrome protein is 1130 aa long (125 kDa). Overall aa sequence identity is 88% with Avena and rice type A phytochromes and 65% with the type A phytochromes of the dicots, pea, zucchini and Arabidopsis. Northern analysis indicates that maize phy transcripts are down-regulated only two- to threefold in etiolated seedlings 3 h after a red light pulse, in contrast to Avena where a ten- to 20-fold decrease is observed. On the other hand, a more than tenfold reduction in maize phy mRNA abundance occurs in seedlings transferred to white light for 24 h. Several conserved sequence elements have been identified by comparison of the maize phyA1 and other monocot phy promoters, suggesting that these common regions may be regulatory elements involved in phy expression.

Amino Acid Sequence↗

PubMed2004

Involvement of lysine-193 of the conserved "K-T-G-G" motif in the catalysis of maize starch synthase IIa.

It has been suggested that the lysine residue in the conserved K-T-G-G motif could be the substrate ADP-glucose binding site of Escherichia coli glycogen synthase (GS). Since the K-X-G-G motif is highly conserved between E. coli GS and all the maize starch synthase (SS) isozymes, it has become widely accepted that the lysine in the conserved K-T-G-G motif may also function as the ADPGlc binding site of maize SS. We have used chemical modification and site-directed mutagenesis to study the function of lysine residues in SS. Pyridoxal-5'-phosphate inactivated maize SSIIa activity in a time and concentration dependent manner. ADPGlc completely protected SSIIa from inactivation by pyridoxal-5'-phosphate, indicating that lysine residue(s) could be important for ADPGlc binding and enzyme catalysis. In contrast to E. coli GS, mutation of conserved lysine193 (K-T-G-G) in maize SS did not alter the ADPGlc binding while significantly changing the enzyme activity toward different primers. Our results suggest that lysine-193 (K-T-G-G) is not directly involved in ADPGlc binding, instead mutation in the conserved lysine position affected the primer preference.

Amino Acid Motifs↗

PubMed2005

Maize cystatins respond to developmental cues, cold stress and drought.

Comprehensive searches of maize EST data allowed us to identify 8 novel Corn Cystatin (CC) genes in addition to the previously known genes CCI and CCII. The deduced amino acid sequences of all 10 genes contain the typical cystatin family signature. In addition, they show an extended overall similarity with cystatins from other species that belong to several different phyto-cystatin subfamilies. To gain further insight into their respective roles in the maize plant, gene-specific expression profiles were established by semi-quantitative RT-PCR. While 7 CC genes were expressed in two or more tissues varying from gene to gene, CCI was preferentially expressed in immature tassels and CC8 and CC10 in developing kernels. As shown by in situ hybridisation of maize kernels, CC8 was specifically expressed in the basal region of the endosperm and CC10 both in the starchy endosperm and the scutellum of the embryo. The remaining, not kernel-specific genes, all had distinct expression kinetics during kernel development, generally with peaks during the early stages. In addition to developmental regulation, the effect of cold stress and water starvation were tested on cystatin expression. Two genes (CC8 and CC9) were induced by cold stress and 5 genes (CCII, CC3, CC4, CC5 and CC9) were down-regulated in response to water starvation. Taken together our data suggest distinct functions for CC genes in the maize plant.

Amino Acid Sequence↗

PubMed2004

Molecular cloning and characterization of a maize transglutaminase complementary DNA.

Two related complementary DNA clones, TGZ15 and TGZ21, encoding active maize transglutaminase (TGase) have been isolated for the first time in plants by molecular cloning (Patent Pending PCT/ES03/00247). Southern and northern blot analyses indicate that the two cDNAs probably corresponded to two different single-copy genes in the maize genome. Northern blot analyses revealed that the transcript is expressed preferentially in young leaves and differentiated embryogenic maize callus. This expression is dependent on light exposure time. TGase activity of the proteins encoded by clones TGZ15 and TGZ21 was detected in bacterial extracts overexpressing them, using two enzymatic assays. TGase activity was significantly higher than that of the empty-phagemid bacterial extracts. As in other TGases, this activity was inhibited by monodansyl cadaverine (MDC), GTP and the absence of exogenous Ca(2+). Likewise, light-stimulated Ca(2+)-dependent TGase activity was detected in thylakoids and grana of maize chloroplast, which was inhibited by MDC, GTP, DIECA and Diuron.

Amino Acid Sequence↗

PubMed2004

ASF/SF2-like maize pre-mRNA splicing factors affect splice site utilization and their transcripts are alternatively spliced.

Three ASF/SF2-like alternative splicing genes from maize were identified, cloned, and analyzed. Each of these genes (zmSRp30, zmSRp31, and zmSRp32) contains two RNA binding domains, a signature sequence SWQDLKD, and a characteristic serine/ariginine-rich domain. There is a strong structural similarity to the human ASF/SF2 splicing factor and to the Arabidopsis atSRp34/p30 proteins. Similar to ASF/SF2-like genes in other organisms, the maize pre-mRNA messages are alternatively spliced. They are differentially expressed in maize tissues with relatively uniform levels of zmSRp30 and zmSRp31 messages being observed throughout the plant, while zmSRp32 messages preferentially accumulated in the meristematic regions. Overexpression of zmSRp32 in maize cells leads to the enhanced selection of weak 5' intron splice sites during the processing of pre-mRNA molecules. Overexpression of the zmSRp31 or zmSRp32 gene affects regulation of wheat dwarf virus rep gene pre-mRNA splicing, presumably by interacting with the weak 5' splice site, CCGU. Our results suggest that the described genes are functional homologues of the human ASF/SF2 alternative splicing factor and they indicate a diversity of the ASF/SF2-like alternative splicing factors in monocot plant cells.

Alternative Splicing↗

PubMed2026

Natural variation in Miniature5 determines mitochondrial nad1 splicing and seed development in maize.

Seed size is a key determinant of cereal grain yield, but natural variations in defective-kernel genes have rarely been applied in maize breeding. Here, we report the positional cloning of maize Miniature5 (Mn5), which encodes a mitochondrial-targeted P-class pentatricopeptide repeat (PPR) protein. Further analysis shows that a missense mutation of Mn5, Mn5Val109, presents in maize populations and correlates with reduced seed size. The Mn5Val109 variant exhibits compromised function in the miniature5 (mn5-ref) mutant, failing to trans-splice mitochondrial nad1 intron1, drastically reducing the abundance and activity of respiratory complex I, accompanied by disorganized mitochondrial cristae. Mn5 directly binds to domain IV of the pre-nad1.1 transcript. Notably, this binding site is located downstream of the previously presumed 3'-terminus bound by MITOCHONDRIA STABILITY/PROCESSING PPR FACTOR1 (MSP1), thus redefining the 3'-end of the nad1.1 pre-RNA. Furthermore, Mn5 physically interacts with the maturases ZmnMAT1 and ZmnMAT3, as well as the PPR proteins PPR-SMR1 and SPR2, which are broadly involved in organellar group II intron splicing. Together, our results suggest that Mn5 recruits maturases and PPR proteins to form spliceosomal complexes responsible for the trans-splicing of nad1 intron1. Importantly, natural variations in Mn5 confer differences in seed size control, offering potential for breeding high-yield maize varieties.

Zea mays↗

PubMed2006

Advances in maize genomics: the emergence of positional cloning.

Positional cloning has been and remains a powerful method for gene identification in Arabidopsis. With the completion of the rice genome sequence, positional cloning in rice also took off, including the cloning of several quantitative trait loci. Positional cloning in cereals such as maize whose genomes are much larger than that of rice was considered near impossible because of the vast amounts of repetitive DNA. However, conservation of synteny across the cereal genomes, in combination with new maize resources, has now made positional cloning in maize feasible. In fact, a chromosomal walk is usually much faster than the more traditional method of gene isolation in maize by transposon tagging.

Chromosome Mapping↗

PubMed2005

Recombinant expression of maize nucleotide excision repair protein Rad23 in Escherichia coli.

Nucleotide excision is a highly conserved DNA repair pathway for correcting DNA lesions that cause distortion of the double helical structure. The protein heterodimer XPC-Rad23 is involved in recognition of and binding to such lesions. We have isolated full-length cDNAs encoding two different members of the maize Rad23 family. The deduced amino acid sequences of both maize orthologues show a high degree of homology to plant and animal Rad23 proteins. The cDNA encoding maize Rad23A was cloned as an in-frame C-terminal fusion of glutathione S-transferase. This chimera was expressed in Escherichia coli as a soluble protein and purified to homogeneity using glutathione-agarose followed by MonoQ column chromatography. Purified recombinant maize Rad23 protein was used to generate polyclonal antibodies that cross-react with a approximately 48-kDa protein in extracts from plant as well as mammalian cells. The purified recombinant protein and antibodies would be useful reagents to study the biochemistry of nucleotide excision repair in plants.

Amino Acid Sequence↗

PubMed2005

Proteome analysis of maize roots reveals that oxidative stress is a main contributing factor to plant arsenic toxicity.

To gain insight into plant responses to arsenic, the effect of arsenic exposure on maize (Zea mays L.) root proteome has been examined. Maize seedlings were fed hydroponically with 300 microM sodium arsenate or 250 microM sodium arsenite for 24 h, and changes in differentially displayed proteins were studied by two-dimensional electrophoresis and digital image analysis. About 10% of total detected maize root proteins (67 out of 700) were up- or down-regulated by arsenic, among which 20 were selected as being quite reproducibly affected by the metalloid. These were analyzed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and 11 of them could be identified by comparing their peptide mass fingerprints against protein- and expressed sequence tag-databases. The set of identified maize root proteins highly responsive to arsenic exposure included a major and functionally homogeneous group of seven enzymes involved in cellular homeostasis for redox perturbation (e.g., three superoxide dismutases, two glutathione peroxidases, one peroxiredoxin, and one p-benzoquinone reductase) besides four additional, functionally heterogeneous, proteins (e.g., ATP synthase, succinyl-CoA synthetase, cytochrome P450 and guanine nucleotide-binding protein beta subunit). These findings strongly suggest that the induction of oxidative stress is a main process underlying arsenic toxicity in plants.

Arsenates↗

PubMed1999

Growth phase-dependent subcellular localization of nitric oxide synthase in maize cells.

A protein band of approximately 166 kDa was detected in the soluble fraction of root tips and young leaves of maize seedlings, based on Western blot analysis using antibodies raised against mouse macrophage nitric oxide synthase (NOS) and rabbit brain NOS. NOS activity was present in these soluble fractions, as determined by L-[U-14C]citrulline synthesis from L[U-14]arginine. Immunofluorescence showed that the maize NOS protein is present in the cytosol of cells in the division zone and is translocated into the nucleus in cells in the elongation zone of maize root tips. These results indicate the existence of a NOS enzyme in maize tissues, with the localization of this protein depending on the phase of cell growth.

Animals↗