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S L Dellaporta

Publications and source records attributed to S L Dellaporta.

At least 19 recordsLinked to original sources
PubMed2001

Maize yellow stripe1 encodes a membrane protein directly involved in Fe(III) uptake.

Frequently, crop plants do not take up adequate amounts of iron from the soil, leading to chlorosis, poor yield and decreased nutritional quality. Extremely limited soil bioavailability of iron has led plants to evolve two distinct uptake strategies: chelation, which is used by the world's principal grain crops; and reduction, which is used by other plant groups. The chelation strategy involves extrusion of low-molecular-mass secondary amino acids (mugineic acids) known as 'phytosiderophores' which chelate sparingly soluble iron. The Fe(III)-phytosiderophore complex is then taken up by an unknown transporter at the root surface. The maize yellow stripe1 (ys1) mutant is deficient in Fe(III)-phytosiderophore uptake, therefore YS1 has been suggested to be the Fe(III)-phytosiderophore transporter. Here we show that ys1 is a membrane protein that mediates iron uptake. Expression of YS1 in a yeast iron uptake mutant restores growth specifically on Fe(III)-phytosiderophore media. Under iron-deficient conditions, ys1 messenger RNA levels increase in both roots and shoots. Cloning of ys1 is an important step in understanding iron uptake in grasses, and has implications for mechanisms controlling iron homeostasis in all plants.

Amino Acid Sequence↗
PubMed2000

Large-scale T-DNA mutagenesis in Arabidopsis for functional genomic analysis.

In planta Agrobacterium-mediated transformation combined with a soil-based herbicide selection for transgenic plants was used to recover large numbers of transgenic Arabidopsis plants for functional genomic studies. A tissue-culture-free system for generating transgenic plants was achieved by infiltrating Arabidopsis plants with Agrobacterium tumefaciens harboring a binary T-DNA vector containing the phosphinothricin acetyltransferase gene from Streptomyces hygroscopicus, and by selecting transgenic Arabidopsis growing in soil by foliar application of the herbicide Finale (phosphinothricin). Analysis of herbicide-resistant plants indicated that all were transgenic and that the T-DNA transformation process occurred late during flower development, resulting in a preponderance of independently derived T-DNA insertions. T-DNA insertions were usually integrated in a concatenated, rearranged form, and using linkage analysis, we estimated that T1 plants carried between one and five T-DNA loci. Using pooling strategies, both DNA and seed pools were generated from about 38,000 Arabidopsis plants representing over 115,000 independent T-DNA insertions. We show the utility of these transgenic lines for identifying insertion mutations using gene sequence and PCR-based screening.

Agrobacterium tumefaciens↗
PubMed1999

Cell death and cell protection genes determine the fate of pistils in maize.

The formation of unisexual flowers in maize requires the selective elimination and sexual maturation of floral organs in an initially bisexual floral meristem. Elimination of pistil primordia occurs in the primary and secondary florets of the tassel spikelets, and in the secondary florets of ear spikelets. Ill-fated pistil cells undergo a cell death process associated with nuclear degeneration in a specific spatial-temporal pattern that begins in the subepidermis, eventually aborting the entire organ. The sex determination genes tasselseed1 and tasselseed2 are required for death of pistil cells. tasselseed1 is required for the accumulation of TASSELSEED2 mRNA in pistil cells. All pistil primordia express TASSELSEED2 RNA but functional pistils found in ear spikelets are protected from cell death by the action of the silkless1 gene. silkless1 blocks tasselseed-induced cell death in the pistil primordia of primary ear florets. A model is proposed for the control of pistil fate by the action of the ts1-ts2-sk1 pathway.

Cell Death↗
PubMed1997

Evidence for a common sex determination mechanism for pistil abortion in maize and in its wild relative Tripsacum.

Cultivated maize (Zea mays) and several other members of the Tribe Andropogoneae produce unisexual florets. In maize, the formation of two staminate florets in each spikelet on the tassel and a single pistillate floret in each spikelet on the ear includes a pistil abortion process that requires the action of the TASSELSEED2 gene. In Eastern gamagrass (Tripsacum dactyloides) the GYNOMONOECIOUS SEX FORM1 gene appears to perform a similar role in pistil abortion. These genes were shown to be homeologs by restriction fragment length polymorphism mapping and by the failure of the gsf1 and ts2 alleles to complement one another in intergeneric hybrids. Molecular analysis of the gsf1 allele shows that it is caused by a 1.4-kb deletion mutation. Both TASSELSEED2 and GYNOMONOECIOUS SEX FORM1 show similar expression patterns in subepidermal cells of pistils just before abortion. These results suggest that the formation of staminate florets in the Andropogoneae represents a monophyletic trait.

Base Sequence↗
PubMed1997

liguleless1 encodes a nuclear-localized protein required for induction of ligules and auricles during maize leaf organogenesis.

The maize ligule and auricle are structures on the maize leaf that develop at the boundary of the sheath and blade. In the absence of liguleless1 (Ig1) gene expression, ligule and auricle are not formed, and the blade-sheath boundary does not develop as an exact line between sheath and blade. By using the Activator (Ac) transposable element as a molecular tag, a novel Ig1 allele, Ig1-m1, was isolated and cloned. Analysis of somatic revertant sectors confirmed that the LG1 gene product functions in a cell-autonomous fashion. cDNA cloning as well as RT-PCR analysis of the LG1 mRNA indicate that the Ig1 gene is expressed at very low levels in the ligular region of developing maize leaf primordia, perhaps as early as plastochron 6 or earlier. Cellular localization studies in a heterologous system indicate that the LG1 product localizes exclusively to the nucleus. The predicted amino acid sequence of the LG1 protein is largely novel but contains an internal domain of 77 amino acids with significant similarity to a domain present in two recently identified SQUAMOSA PROMOTER-BINDING proteins 1 and 2 (SBP1 and SBP2) in Antirhinum majus.

Alleles↗
PubMed1997

Ectopic anthocyanin pigmentation in maize as a tool for defining interactions between homologous regulatory factors.

The duplicated R and Sn genes are involved in the regulation of the maize anthocyanin biosynthetic pathway, encoding tissue-specific products that are homologous to the helix-loop-helix transcriptional activators. Sn determines the pigmentation of the mesocotyl, leaf basis and pericarp, while R determines pigmentation in various tissues, but not in the mesocotyl. In the progeny derived from test-crosses of R/Sn heterozygous plants, a high frequency of R plants exhibiting mesocotyl pigmentation was observed; these derivatives were defined as R*. In R* plants, the presence of this novel trait was not accompanied by the acquisition of Sn or by gross DNA rearrangements in the R profile. Accordingly, RT-PCR analysis showed that mesocotyl pigmentation in R* was attributable to the resident R gene. The occurrence of R* was observed with all R alleles tested, and was enhanced when a P component was present. The heritability of R* was shown only in the case of the standard R-r allele, which carries a functional P component. In addition, we observed that R* can influence other R alleles, transferring the ability to pigment the mesocotyl. R* is unstable, showing a tendency to return to its original state after a few generations. In R* plants there was a correlation between observed ectopic pigmentation and an increase in the level of A1 transcript but, surprisingly, not in the accumulation of R transcript. The results obtained from the analysis of test crosses of rSn/r delta plants suggest that an unlinked genetic factor accounts for the ectopic pigmentation. Concomitant occurrence of epigenetic events might explain the observed instability and reversibility noted above. Further study of this phenomenon might help to elucidate the basis of the interaction between homologous and non-homologous regulators.

Anthocyanins↗
PubMed1997

Insertions of a novel class of transposable elements with a strong target site preference at the r locus of maize.

The r locus of maize regulates anthocyanin synthesis in various tissues of maize through the production of helix-loop-helix DNA binding proteins capable of inducing expression of structural genes in the anthocyanin biosynthetic pathway. The complex r variant, R-r: standard (R.r), undergoes frequent mutation through a variety of mechanisms including displaced synapsis and crossing over, and intrachromosomal recombination. Here we report a new mechanism for mutation at the R-r complex: insertion of a novel family of transposable elements. Because the elements were first identified in the R-p gene of the R-r complex, they have been named P instability Factor (PIF). Two different PIF elements were cloned and found to have identical sequences at their termini but divergent internal sequences. In addition, the PIF elements showed a marked specificity of insertion sites. Six out of seven PIF-containing derivatives examined had an element inserted at an identical location. Two different members of the PIF element family were identified at this position. The seventh PIF-containing derivative examined had the element inserted at a distinct position within r. Even at this location, however, the element inserted into a conserved target sequence. The timing of PIF excision is unusual. Germinal excision rates can range up to several percent of progeny. Yet somatic sectors are rare, even in lines exhibiting high germinal reversion rates.

Anthocyanins↗
PubMed1997

The Ac-st2 element of maize exhibits a positive dosage effect and epigenetic regulation.

A novel derivative of the maize transposable element Ac, termed Ac-st2, that displays a positive dosage effect in maize has been identified. Although identical in sequence to other Ac elements, increasing the copy number of the element in the endosperm results in earlier and more frequent Ds excision. Ac-st2 autonomously transposes and catalyzes somatic excision of Ds elements. Germinal transpositions of either Ac-st2 or Ds, however, were not observed. The Ac-st2 phenotype includes a reduction in Ac transcript accumulation that is associated with increased methylation at specific sites in the promoter region of the major transcriptional start site within Ac (ORFa). This element differs from metastable (cycling) Ac derivatives in that Ac-st2 conditions a uniform transposition pattern throughout endosperm and plant development. Ac-st2 undergoes frequent increases in activity after its association with an active Ac element. This change in activity correlates with reduced levels of methylation in the ORFa promoter region. Using a competitive PCR assay, Ac transcript accumulation was followed through endosperm development. From these data, a model is proposed to explain the patterns of variegation associated with both "wild type" active Ac and Ac-st2 elements.

DNA Methylation↗
PubMed1996

Demethylation-induced developmental pleiotropy in Arabidopsis.

The function of DNA methylation in higher plants was investigated by expression of a complementary DNA encoding a cytosine methyltransferase (MET1) from Arabidopsis thaliana as an antisense RNA in transgenic plants. This expression resulted in a 34 to 71 percent reduction in total genomic cytosine methylation. Loss of methylation was observed in both repetitive DNA and single-copy gene sequences. Developmental effects included altered heterochrony, changes in meristem identity and organ number, and female sterility. Cytosine demethylation prolonged both vegetative and reproductive phases of development. These findings implicate DNA methylation in establishing or maintaining epigenetic developmental states in the meristem.

5-Methylcytosine↗
PubMed1996

Leaf permease1 gene of maize is required for chloroplast development.

Adjacent bundle sheath and mesophyll cells cooperate for carbon fixation in the leaves of C4 plants. Mutants with compromised plastid development should reveal the degree to which this cooperation is obligatory, because one can assay whether mesophyll cells with defective bundle sheath neighbors retain C4 characteristics or revert to C3 photosynthesis. The leaf permease1-mutable1 (lpe1-m1) mutant of maize exhibits disrupted chloroplast ultrastructure, preferentially affecting bundle sheath choroplasts under lower light. Despite the disrupted ultrastructure, the metabolic cooperation of bundle sheath and mesophyll cells for C4 photosynthesis remains intact. To investigate this novel mutation, the Activator transposon-tagged allele and cDNAs corresponding to the Lpe1 mRNA from wild-type plants were cloned. The Lpe1 gene encodes a polypeptide with significant similarity to microbial pyrimidine and purine transport proteins. An analysis of revertant sectors generated by Activator excision suggests that the Lpe1 gene product is cell autonomous and can be absent up to the last cell divisions in the leaf primordium without blocking bundle sheath chloroplast development.

Amino Acid Sequence↗
PubMed1995

Transposon-mediated chromosomal rearrangements and gene duplications in the formation of the maize R-r complex.

R-r controls the production of anthocyanin pigment in plant parts and the aleurone layer of seeds through the production of a family of related transcriptional activating proteins of the helix-loop-helix type. The R-r complex comprises a series of repeated, homologous components arranged in both direct and inverted orientations. These include the P component, a simple R gene that confers pigmentation of plant parts, and the S subcomplex that consists of a truncated inactive R gene called q, and two functional R genes, S1 and S2, that pigment the aleurone. The S genes are arranged in an unusual inverted head-to-head orientation. The identity of each functional component was confirmed by microprojectile bombardment of intact maize tissues with cloned genomic DNA and by analysis of in vivo mRNA populations. Sequence analysis suggests that the S subcomplex was derived through the rearrangement of a simple P-like progenitor element. At the rearrangement breakpoints, features typical of the CACTA family of transposable elements were found. The location and arrangement of these CACTA element sequences implies that this element may have mediated the chromosomal rearrangements that led to the formation of the R-r complex. The unusual structure of R-r explains much of the meiotic instability of the complex.

Anthocyanins↗
PubMed1994

The sex determination process in maize.

Maize partitions the sexes into different flowers on the plant, a condition called monoecy, which facilitates outcrossing. Sex determination in maize is a complex process involving an interplay between genetic determinants, the environment, and hormones. Unisexuality of flowers is achieved by the process of selective arrest and abortion of the inappropriate organ primordia within a bisexual floral meristem. Floral organ abortion is associated with the degeneration of cells within an immature primordia. Masculinizing genes are required for gynoecial abortion, feminizing genes arrest stamen development, and both types also control secondary sexual traits involving morphological characteristics of floral tissues. Gibberellins, steroid-like plant hormones, appear to play a pivotal role in the stamen abortion process and the feminization of floral tissues.

Genes, Plant↗
PubMed1994

Somatic inactivation and reactivation of Ac associated with changes in cytosine methylation and transposase expression.

Several metastable Ac alleles at the maize p locus were identified that produced novel pericarp variegation patterns. From the transmission analysis of pericarp sectors, we show that Ac inactivation is a somatic process. Ac excision from P and transactivation of an unlinked Ds was delayed or absent in plants with metastable Ac alleles. These decreases in Ac activity were correlated to increases in cytosine methylation at specific sites near the start of Ac transcription (open reading frame a; ORFa) and at sites in some flanking P sequence. Reactivation of inactive alleles was accompanied by decreased methylation of Ac and P sequences. Using a competitive polymerase chain reaction assay, steady state levels of ORFa transcript were quantitatively compared among the various metastable alleles. We propose that changes in the methylation profile of Ac correspond to changes in Ac activity through the differential accumulation of Ac transcript.

Alleles↗
PubMed1993

Sex determination gene TASSELSEED2 of maize encodes a short-chain alcohol dehydrogenase required for stage-specific floral organ abortion.

Maize produces separate unisexual flowers through programmed abortion of preformed organ primordia. In the male inflorescence (tassel), stamen primordia develop to sexual maturity, while gynoecia (pistil primordia) are aborted. In tasselseed2 (ts2) mutant plants, floral structures in the tassel adopt a female developmental program. Here we report the transposon tagging and cloning of the TS2 gene, which plays a late but pivotal role in determining the sexual fate of floral meristems. Shortly before abortion of the gynoecium, Ts2 mRNA is expressed subepidermally in that primordium. Phenotypic instability of the Activator (Ac)-induced allele ts2-m1 indicates that late restoration of TS2 action in somatic tissues, which is correlated with Ac excision, reactivates the male developmental program. The predicted amino acid sequence of the Ts2 protein shows significant similarity to short-chain alcohol dehydrogenases, particularly hydroxysteroid dehydrogenases.

Alcohol Dehydrogenase↗
PubMed1993

Sex determination in flowering plants.

In many ways, plants offer unique systems through which to study sex determination. Because the production of unisexual flowers has evolved independently in many plant species, different and novel mechanisms may be operational. Hence, there is probably not one unifying mechanism that explains sex determination in plants. Advances in our understanding of sex determination will come from the analysis of the genetics, molecular biology, and biochemistry of genes controlling sexual determination in plants. Several excellent model systems for bisexual floral development (Arabidopsis and Antirrhinum), monoecy (maize), and dioecy (Silene, asparagus, and mercury) are available for such analyses. The important questions that remain concern the mechanism of action of sex determination genes and their interrelationship, if any, with homeotic genes that determine the sexual identity of floral organ primordia. At the physiological level, the connection between hormone signaling and sexuality is not well understood, although significant correlations have been discovered. Finally, once the genes that regulate these processes are identified, cloned, and studied, new strategies for the manipulation of sexuality in plants should be forthcoming.

Biological Evolution↗
PubMed1993

Determination of paternity in dragonflies by Random Amplified Polymorphic DNA fingerprinting.

We used Random Amplified Polymorphic DNA (RAPD) fingerprinting to address issues of paternity in two odonate species. Amplification artifacts of RAPD markers were controlled by assessing paternity patterns relative to the banding patterns generated by quantitative mixtures of DNA from putative parents ('synthetic offspring'). In the aeshnid dragonfly Anax parthenope, for which the mating histories of both males and females were unknown, we found strong evidence for complete paternity success for the contact guarding male. In the highly polygamous libellulid dragonfly Orthetrum coerulescens, we detected and quantified mixed paternity in sequentially produced offspring clutches and demonstrated that fertilization success is correlated with the duration of copulation. Our results suggest that RAPD fingerprinting is suitable to address issues of paternity in systems which are genetically uncharacterized and produce large offspring clutches.

Animals↗
PubMed1992

Molecular analysis of Ac transposition and DNA replication.

Molecular events associated with transposition of the mobile element Activator (Ac) from the P locus of maize have been examined in daughter lineages of twinned sectors. Genetic and molecular analyses indicate that the donor Ac has excised from only one of the two daughter chromosomes in these lineages. Cloning and sequence analyses of target sites on daughter chromosomes indicate that Ac insertion can occur either before or after the completion of DNA replication. Transpositions from a replicated donor site to both unreplicated and replicated target sites imply that most transpositions of Ac occur during or shortly after the S phase of the cell cycle.

Base Sequence↗