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A Mouras

Publications and source records attributed to A Mouras.

13 recordsLinked to original sources
PubMed2001

Inhibition of cell proliferation, cell expansion and differentiation by the Arabidopsis SUPERMAN gene in transgenic tobacco plants.

Plant development depends upon the control of growth, organization and differentiation of cells derived from shoot and root meristems. Among the genes involved in flower organ determination, the cadastral gene SUPERMAN controls the boundary between whorls 3 and 4 and the growth of the adaxial outer ovule integument by down-regulating cell divisions. To determine the precise function of this gene we overexpressed ectopically the Arabidopsis thaliana (L.) Heynh. SUPERMAN gene in tobacco (Nicotiana tabacum L.). The transgenic plants exhibited a dwarf phenotype. Histologically and cytologically detailed analyses showed that dwarfism is correlated with a reduction in cell number, which is in agreement with the SUPERMAN function in Arabidopsis. Furthermore, a reduction in cell expansion and an impairment of cell differentiation were observed in tobacco organs. These traits were observed in differentiated vegetative and floral organs but not in meristem structures. A potential effect of the SUPERMAN transcription factor in the control of gibberellin biosynthesis is discussed.

Arabidopsis↗
PubMed2001

Defective cell proliferation in the floral meristem of alloplasmic plants of Nicotiana tabacum leads to abnormal floral organ development and male sterility.

Flowers of an alloplasmic male-sterile tobacco line, comprised of the nuclear genome of Nicotiana tabacum and the cytoplasm of Nicotiana repanda, develop short, poorly-pigmented petals and abnormal sterile stamens that often are fused with the carpel wall. The development of flower organ primordia and establishment of boundaries between the different zones in the floral meristem were investigated by performing expression analysis of the tobacco orthologs of the organ identity genes GLO, AG and DEF. These studies support the conclusion that boundary formation was impaired between the organs produced in whorls 3 and 4 resulting in partial fusions between anthers and carpels. According to the investigations cell divisions and floral meristem size in the alloplasmic line were drastically reduced in comparison with the male-fertile tobacco line. The reduction in cell divisions leads to a discrepancy between cell number and cell determination at the stage when petal and stamen primordia should be initiated. At the same stage expression of the homeotic genes was delayed in comparison with the male-fertile line. However, the abnormal organ development was not due to a failure in the spatial expression of the organ identity genes. Instead the aberrant development in the floral organs of whorls 2, 3 and 4 appears to be caused by deficient floral meristem development at an earlier stage. Furthermore, defects in cell proliferation in the floral meristem of the alloplasmic male-sterile line correlates with presence of morphologically modified mitochondria. The putative causes of reduced cell number in the floral meristem and the consequences for floral development are discussed.

Cell Division↗
PubMed2001

A new C-type cyclin-dependent kinase from tomato expressed in dividing tissues does not interact with mitotic and G1 cyclins.

Cyclin-dependent kinases (CDKs) form a conserved superfamily of eukaryotic serine-threonine protein kinases whose activity requires the binding of a cyclin protein. CDKs are involved in many aspects of cell biology and notably in the regulation of the cell cycle. Three cDNAs encoding a C-type CDK, and a member of each B-type CDK subfamily, were isolated from tomato (Lycopsersicon esculentum Mill.) and designated Lyces;CDKC;1 (accession no. AJ294903), Lyces; CDKB1;1 (accession no. AJ297916), and Lyces;CDKB2;1 (accession no. AJ297917). The predicted amino acid sequences displayed the characteristic PITAIRE (CDKC), PPTALRE (CDKB1), and PPTTLRE (CDKB2) motives in the cyclin-binding domain, clearly identifying the type of CDK. The accumulation of all transcripts was associated preferentially with dividing tissues in developing tomato fruit and vegetative organs. In contrast to that of CDKA and CDKBs, the transcription pattern of Lyces;CDKC;1 was shown to be independent of hormone and sugar supply in tomato cell suspension cultures and excised roots. This observation, together with the absence of a patchy expression profile in in situ hybridization experiments, suggests a non-cell cycle regulation of Lyces;CDKC;1. Using a two-hybrid assay, we showed that Lyces;CDKC;1 did not interact with mitotic and G1 cyclins. The role of plant CDKCs in the regulation of cell division and differentiation is discussed with regard to the known function of their animal counterparts.

Amino Acid Sequence↗
PubMed1999

SlY1, the first active gene cloned from a plant Y chromosome, encodes a WD-repeat protein.

Unlike the majority of flowering plants, which possess hermaphrodite flowers, white campion (Silene latifolia) is dioecious and has flowers of two different sexes. The sex is determined by the combination of heteromorphic sex chromosomes: XX in females and XY in males. The Y chromosome of S.latifolia was microdissected to generate a Y-specific probe which was used to screen a young male flower cDNA library. We identified five genes which represent the first active genes to be cloned from a plant Y chromosome. Here we report a detailed analysis of one of these genes, SlY1 (S.latifolia Y-gene 1). SlY1 is expressed predominantly in male flowers. A closely related gene, SlX1, is predicted to be located on the X chromosome and is strongly expressed in both male and female flowers. SlY1 and SlX1 encode almost identical proteins containing WD repeats. Immunolocalization experiments showed that these proteins are localized in the nucleus, and that they are most abundant in cells that are actively dividing or beginning to differentiate. Interestingly, they do not accumulate in arrested sexual organs and represent potential targets for sex determination genes. These genes will permit investigation of the origin and evolution of sex chromosomes in plants.

Amino Acid Sequence↗
PubMed1999

Sexual dimorphism in white campion: deletion on the Y chromosome results in a floral asexual phenotype.

White campion is a dioecious plant with heteromorphic X and Y sex chromosomes. In male plants, a filamentous structure replaces the pistil, while in female plants the stamens degenerate early in flower development. Asexual (asx) mutants, cumulating the two developmental defects that characterize the sexual dimorphism in this species, were produced by gamma ray irradiation of pollen and screening in the M1 generation. The mutants harbor a novel type of mutation affecting an early function in sporogenous/parietal cell differentiation within the anther. The function is called stamen-promoting function (SPF). The mutants are shown to result from interstitial deletions on the Y chromosome. We present evidence that such deletions tentatively cover the central domain on the (p)-arm of the Y chromosome (Y2 region). By comparing stamen development in wild-type female and asx mutant flowers we show that they share the same block in anther development, which results in the production of vestigial anthers. The data suggest that the SPF, a key function(s) controlling the sporogenous/parietal specialization in premeiotic anthers, is genuinely missing in females (XX constitution). We argue that this is the earliest function in the male program that is Y-linked and is likely responsible for "male dimorphism" (sexual dimorphism in the third floral whorl) in white campion. More generally, the reported results improve our knowledge of the structural and functional organization of the Y chromosome and favor the view that sex determination in this species results primarily from a trigger signal on the Y chromosome (Y1 region) that suppresses female development. The default state is therefore the ancestral hermaphroditic state.

Chromosome Deletion↗
PubMed1998

Impairment of tapetum and mitochondria in engineered male-sterile tobacco plants.

Flowers of tobacco transformed with an unedited copy of the mitochondrial atp9 gene sequence fused to the yeast coxIV mitochondrial targeting presequence, showed several anther abnormalities leading to pollen abortion. The gene was expressed in vegetative and reproductive tissues of the plant. Cytological analysis revealed that tapetum development was impaired. Mitochondria of the tapetum cells were severely affected showing characteristic signs of degeneration: loss of cristae and swelling. These mitochondrial modifications were correlated with the presence of the transcript and translated product of the 'unedited' atp9 and a significant decrease in oxygen consumption in non-photosynthetic tissues. The main effect of the unedited atp9 expression in transgenic plants was male sterility.

Arabidopsis Proteins↗
PubMed1997

Microdissection and amplification of coding sequences from a chromosome fragment restoring male fertility in alloplasmic male-sterile tobacco.

An alloplasmic male-sterile line of tobacco, containing the nucleus of Nicotiana tabacum and the cytoplasm of Nicotiana repanda, is restored to fertility by introgression of an alien chromosome fragment obtained from the cytoplasm donor. To isolate the restorer gene(s), the alien chromosome fragment was microdissected from metaphase plates of the restored line. The microdissected chromosomes represented only 0.1 pg of DNA, which was amplified using a degenerate oligonucleotide-primed PCR method (DOP-PCR), from which a chromosome fragment specific library was created. Compared with previous strategies used for microcloning, a modified and improved method was developed by the subsequent isolation of expressed sequences. The library was screened with cDNA probes synthesized by reverse transcription and DOP-PCR amplification (RT/DOP-PCR), of total RNAs isolated from early developing restored and male-sterile flower buds. By this strategy, transcribed DNA sequences specific for the restored line were cloned.

Chromosomes↗
PubMed1997

Isolation of early genes expressed in reproductive organs of the dioecious white campion (Silene latifolia) by subtraction cloning using an asexual mutant.

The dioecious white campion (Silene latifolia) has been chosen as a working model for sexual development. In this species, sexual dimorphism is achieved through two distinct developmental blocks: inhibition of carpel development in male flowers, and early arrest of anther differentiation in female flowers. The combined advantages of the dioecious system and the availability of a sexual mutant lacking both male and female reproductive organs have been exploited in a molecular subtraction approach using male and asexual flower buds. This resulted in the cloning of 22 cDNA clones expressed in stamens at distinct stages of development. Fourteen of these clones corresponded to genes whose expression was detected in pre-meiotic stamens, a stage of development for which very little information is presently available. Furthermore, the absence of similarities with database sequences for ten clones suggests that they represent novel genes. Functional analysis of each clone will enable their positioning within the reproductive organ developmental pathway(s). In parallel, these clones are being exploited as developmental markers of early differentiation within the flower.

Blotting, Southern↗
PubMed1996

Transgenic male-sterile plant induced by an unedited atp9 gene is restored to fertility by inhibiting its expression with antisense RNA.

We have previously shown that the expression of an unedited atp9 chimeric gene correlated with male-sterile phenotype in transgenic tobacco plant. To study the relationship between the expression of chimeric gene and the male-sterile trait, hemizygous and homozygous transgenic tobacco lines expressing the antisense atp9 RNA were constructed. The antisense producing plants were crossed with a homozygous male-sterile line, and the F1 progeny was analyzed. The offspring from crosses between homozygous lines produced only male-fertile plants, suggesting that the expression antisense atp9 RNA abolishes the effect of the unedited chimeric gene. In fact, the plants restored to male fertility showed a dramatic reduction of the unedited atp9 transcript levels, resulting in normal flower development and seed production. These results support our previous observation that the expression of unedited atp9 gene can induce male sterility.

Base Sequence↗
PubMed1995

RNA editing in wheat mitochondria.

C to U transitions in plant mitochondrial mRNA (RNA editing) lead to amino acid changes as well as to the creation of new initiation or termination codons. We established an in vitro system to assay and to dissect the process of wheat mitochondrial mRNA editing. A deamination mechanism explains most easily the observed C to U transitions. Several fractions of organellar protein participate in the editing machinery. Some of these proteins presumably carry the catalytic activity while others are typical RNA binding proteins and may confer specificity to the 'editosome' complex. To investigate the functional properties of protein products synthesized from unedited mRNAs, we constructed transgenic tobacco plants carrying an unedited gene coding for subunit 9 (ATP9) of the ATP synthase complex. The nuclear encoded 'unedited' protein product is targeted to the mitochondria with a heterologous presequence. A significant number of male sterile tobacco plants were obtained suggesting that at least the functional ATP9 protein requires RNA editing. This result suggests a novel approach to obtain artificial male sterile plants by using a physiological effect resulting in CMS which mimics the situation found in many natural populations.

Codon, Initiator↗
PubMed1993

Male-sterility induction in transgenic tobacco plants with an unedited atp9 mitochondrial gene from wheat.

Cytoplasmic male sterility in plants is associated with mitochondrial dysfunction. We have proposed that a nuclear-encoded chimeric peptide formed by mitochondrial sequences when imported into the mitochondria may impair organelle function and induce male sterility in plants. A model developed to test this hypothesis is reported here. Assuming that the editing process in higher plant mitochondria reflects a requirement for producing active proteins, we have used edited and unedited coding sequences of wheat ATP synthase subunit 9 (atp9) fused to the coding sequence of a yeast coxIV transit peptide. Transgenic plants containing unedited atp9 exhibited either fertile, semifertile, or male-sterile phenotypes; controls containing edited atp9 or only the selectable marker gave fertile plants. Pollen fertility ranged from 31% to 75% in fertile plants, 10% to 20% in semifertile plants, and < 2% in male-sterile plants. Genetic and molecular data showed that the chimeric plasmid containing the transgene is inherited as a Mendelian trait. The transgenic protein is imported into the mitochondria. The production and frequency of semifertile or male-sterile transgenic plants conform to the proposed hypothesis.

Amino Acid Sequence↗
PubMed1993

DNA methylation of sex chromosomes in a dioecious plant, Melandrium album.

Melandrium album, a dioecious plant species, has two heteromorphic sex chromosomes with the XY constitution typical for male and the XX for female plants. This plant represents an experimental model system of sex determination in which the Y chromosome plays a strongly dominant male role. We present data on the overall transcriptional activities of M. album sex chromosomes. DNA methylation patterns were analysed directly at the level of chromosomes using in situ nick-translation of fixed root mitotic chromosomes after nuclease digestion and in vivo labelling with S-adenosyl-L-[methyl-3H] methionine as donor of methyl groups. Both techniques revealed that the two X chromosomes of female plants had different levels of DNA methylation. Cell treatment with a DNA hypomethylating drug, 5-azacytidine, significantly influenced the labelling densities. These results imply that in female M. album plants, one of the two X chromosomes may be hypermethylated and inactive as described for mammalian cells (Lyon hypothesis). A similar analysis made on male cells displayed a similar relative levels of methylation in autosomes and sex chromosomes, thus indicating the transcriptional activity of both Y and X male chromosomes.

DNA↗