Expression, regulation and activity of a B2-type cyclin in mitotic and endoreduplicating maize endosperm.

Cyclin-dependent kinases, the master regulators of the eukaryotic cell cycle, are complexes comprised of a catalytic serine/threonine protein kinase and an essential regulatory cyclin. The maize genome encodes over 50 cyclins grouped in different types, but they have been little investigated. We characterized a type B2 cyclin (CYCB2;2) during maize endosperm development, which comprises a cell proliferation phase based on the standard mitotic cell cycle, followed by an endoreduplication phase in which DNA replication is reiterated in the absence of mitosis or cytokinesis.

Cell cycle control and seed development.

Seed development is a complex process that requires coordinated integration of many genetic, metabolic, and physiological pathways and environmental cues. Different cell cycle types, such as asymmetric cell division, acytokinetic mitosis, mitotic cell division, and endoreduplication, frequently occur in sequential yet overlapping manner during the development of the embryo and the endosperm, seed structures that are both products of double fertilization. Asymmetric cell divisions in the embryo generate polarized daughter cells with different cell fates.

Cyclin-dependent kinase complexes in developing maize endosperm: evidence for differential expression and functional specialization.

Endosperm development in maize (Zea mays L.) and related cereals comprises a cell proliferation stage followed by a period of rapid growth coupled to endoreduplication. Regulation of the cell cycle in developing endosperm is poorly understood.

Control of cell proliferation, endoreduplication, cell size, and cell death by the retinoblastoma-related pathway in maize endosperm.

The endosperm of cereal grains is one of the most valuable products of modern agriculture. Cereal endosperm development comprises different phases characterized by mitotic cell proliferation, endoreduplication, the accumulation of storage compounds, and programmed cell death. Although manipulation of these processes could maximize grain yield, how they are regulated and integrated is poorly understood.

The contribution of cell cycle regulation to endosperm development.

Development of the seed endosperm involves several different types of coordinated cell cycle programs: acytokinetic mitosis, which produces a syncytium soon after fertilization; cellularization through the formation of modified phragmoplasts; cell proliferation, in which mitosis is coupled to cell division; and, in certain species like cereal crops, endoreduplication. Understanding the regulation of these programs and their transitions is challenging, but it has the potential to define important links between the cell cycle, cell differentiation and development, as well as provide tools for the manipulation of seed yield. A relatively large number of mutants display endosperm proliferation defects, and connections with known cell cycle genes are beginning to emerge.

Positive regulation of minichromosome maintenance gene expression, DNA replication, and cell transformation by a plant retinoblastoma gene.

Retinoblastoma-related (RBR) genes inhibit the cell cycle primarily by repressing adenovirus E2 promoter binding factor (E2F) transcription factors, which drive the expression of numerous genes required for DNA synthesis and cell cycle progression. The RBR-E2F pathway is conserved in plants, but cereals such as maize are characterized by having a complex RBR gene family with at least 2 functionally distinct members, RBR1 and RBR3. Although RBR1 has a clear cell cycle inhibitory function, it is not known whether RBR3 has a positive or negative role.

Grasses like mammals? Redundancy and compensatory regulation within the retinoblastoma protein family.

The retinoblastoma (RB) protein family plays a conserved and inhibitory role in cell cycle progression in higher eukaryotes. In mammals, this family includes, in addition to RB, the related (RBR) proteins p107 and p130, which appear to have both specific and redundant functions compared to those of the prototypical RB protein. Whereas most plant species seem to possess only one RBR gene, a recent study has shown that in maize there are two types of distinctly regulated RBR proteins, RBR1 and RBR3.

RBR3, a member of the retinoblastoma-related family from maize, is regulated by the RBR1/E2F pathway.

Retinoblastoma-related (RBR) proteins regulate cell division in higher eukaryotes by controlling the adenovirus E2 promoter binding factor (E2F)/dimerization partner (DP) family of transcription factors that regulate expression of many genes involved in cell-cycle progression. We identified a previously undescribed member of the maize RBR family, RBR3, which has the characteristic structure and binding activities of pocket proteins, where interaction depends on a LxCxE motif in the partner proteins and a critical cysteine within the B pocket domain. Like other RBR proteins, RBR3 appears to be regulated by phosphorylation mediated by cyclin-dependent kinases.

Cyclin-dependent kinase inhibitors in maize endosperm and their potential role in endoreduplication.

Two maize (Zea mays) cyclin-dependent kinase (CDK) inhibitors, Zeama;KRP;1 and Zeama;KRP;2, were characterized and shown to be expressed in developing endosperm. Similar to the CDK inhibitors in Arabidopsis (Arabidopsis thaliana) and tobacco (Nicotiana tabacum), the maize proteins contain a carboxy-terminal region related to the inhibitory domain of the mammalian Cip/Kip inhibitors. Zeama;KRP;1 is present in the endosperm between 7 and 21 d after pollination, a period that encompasses the onset of endoreduplication, while the Zeama;KRP;2 protein declines during this time.

A dominant negative mutant of cyclin-dependent kinase A reduces endoreduplication but not cell size or gene expression in maize endosperm.

Cells in maize (Zea mays) endosperm undergo multiple cycles of endoreduplication, with some attaining DNA contents as high as 96C and 192C. Genome amplification begins around 10 d after pollination, coincident with cell enlargement and the onset of starch and storage protein accumulation. Although the role of endoreduplication is unclear, it is thought to provide a mechanism that increases cell size and enhances gene expression.

Molecular cloning and characterisation of a maize cDNA for a homologue of the large subunit of the eukaryotic initiation factor 3 (eIF3).

In order to identify genes that are specifically expressed in distinct cell populations of the maize root apex, we have constructed PCR-directed cDNA libraries from microdissected populations of cells, and screened them by differential hybridisation. A meristem-specific cDNA was isolated and characterised. This cDNA, termed ZmeIF3A, encodes a protein homologous to the large subunit of the eukaryotic translation Initiation Factor 3 (eIF3), which is an essential multi-protein complex for the initiation of protein synthesis.

Annexin-like protein from Arabidopsis thaliana rescues delta oxyR mutant of Escherichia coli from H2O2 stress.

Reactive oxygen species are common causes of cellular damages in all aerobic organisms. In Escherichia coli, the oxyR gene product is a positive regulator of the oxyR regulon that is induced in response to H2O2 stress. To identify genes involved in counteracting oxidative stress in plants, we transformed a delta oxyR mutant of E.

cDNA cloning and characterisation of a maize homologue of the MCM proteins required for the initiation of DNA replication.

A central question in cell cycle regulation is how DNA replication is initiated and executed only once in each cell cycle. The cell cycle-regulated assembly of specific initiation protein complexes at chromosomal origins appears to specify the initial sites and timing of DNA replication, and to restrict this process to only one round in the somatic cell cycle. Among the enzymes involved in origin activation, the MCM proteins play a conserved key role.

The resistance of cowpea seeds to bruchid beetles is not related to levels of cysteine proteinase inhibitors.

A cDNA encoding a cysteine proteinase inhibitor was isolated from a cDNA library prepared from developing seeds of an insect-resistant line of cowpea. The sequence of the encoded protein was homologous with those of other plant cysteine endoproteinase inhibitors, and with Type 2 cystatins from animals. Southern blot analyses indicated that small gene families were present in both resistant and susceptible lines of cowpea, while northern blot analyses showed similar levels of expression.

Molecular analyses of a barley multigene family homologous to the yeast protein kinase gene SNF1.

Genomic sequences homologous to the yeast gene SNF1 have been isolated from barley (Hordeum vulgare) cv. Sunbar. SNF1 encodes a protein serine/threonine kinase required for the derepression of a number of genes, including SUC2 (invertase) in response to glucose deprivation.

Restriction fragment analysis of 'null' forms at the Gli-1 loci of bread and durum wheats.

Wheat accessions lacking some of the ω- and γ-gliadin components encoded by the Gli-1 loci on the short arm of chromosome 1D in bread wheat and chromosome 1A in durum wheat were studied by two-dimensional polyacrylamide gel electrophoresis and restriction fragment analysis. Digested genomic DNAs of 'normal' and 'null' forms were probed with a cDNA clone related to ω-/γ-gliadins and with a genomic clone encoding an LMW subunit of glutenin. The hybridisation patterns with the ω-/γ-gliadin probe were similar to those of cvs 'Chinese Spring' and 'Langdon' used as standards for bread and durum wheats, respectively, but several restriction fragments located on the 1D chromosome of bread wheat and the 1A chromosome of durum wheat were absent in the 'null' forms.

Restriction fragment analysis of the secalin loci of rye.

Analyses of wheat/rye addition lines by Southern blotting confirmed the presence of sequences related to the Sec 1, Sec 2, and Sec 3 loci on chromosomes 1R and 2R. Comparison of the 1R and 2R addition lines allowed the identification of gamma-secalin genes at Sec 1 and Sec 2, respectively, while omega-secalin and gamma-secalin genes at Sec 1 were discriminated by comparative hybridization with three probes: omega-secalin, total gamma-secalin, and 3' gamma-secalin. The high molecular weight (HMW) secalin genes at Sec 3 were identified using a homologous HMW subunit probe from wheat.

Characterization and organization of gene families at the Gli-1 loci of bread and durum wheats by restriction fragment analysis.

Probes related to γ-gliadins and to the LMW subunits of glutenin were used to determine the complexity of the Gli-1 loci, by RFLP analysis of euploid and aneuploid lines of bread wheat cv Chinese Spring and durum wheat cv Langdon. The two probes hybridised to separate sets of fragments derived from chromosomes 1 A, 1 B and 1D. The fragments related to the LMW subunit probe had a total copy number in HindIII digests of about 35 in Chinese Spring and 17 in Langdon, with more fragments derived from chromosomes 1D.

Complementation of snf1, a mutation affecting global regulation of carbon metabolism in yeast, by a plant protein kinase cDNA.

A cDNA, cRKIN1, encoding a putative homologue of the yeast (Saccharomyces cerevisiae) SNF1-encoded protein-serine/threonine kinase, has been isolated from a library prepared from rye endosperm mRNA. Northern blot analysis demonstrated the presence of cRKIN1-related transcripts in developing endosperms but not in shoots, and Southern blot analysis showed the presence of a small gene family. SNF1 plays a central role in carbon catabolite repression in yeast and expression of the RKIN1 sequence in yeast snf1 mutants restored SNF1 function.

Chromosomal location of seed storage protein genes in the genome ofDasypyrum villosum (L.) Candargy.

Genes coding for glutenin-like subunits and for several prolamin subunits with electrophoretic mobilities (lactate-PAGE) corresponding to those of omega- and gamma-gliadins of wheat were located inDasypyrum villosum chromosome1V. Genes controlling four gliadinlike subunits with electrophoretic mobilities corresponding to those of alpha- and gamma-gliadins were located on the short arm of chromosome6V and on the long arm of chromosome4V. N-terminal amino acid sequences of these four components were also determined and homology with alpha-type gliadins was demonstrated.