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D Weigel

Publications and source records attributed to D Weigel.

At least 19 recordsLinked to original sources
PubMed1998

A genetic framework for floral patterning.

The initial steps of flower development involve two classes of consecutively acting regulatory genes. Meristem-identity genes, which act early to control the initiation of flowers, are expressed throughout the incipient floral primordium. Homeotic genes, which act later to specify the identity of individual floral organs, are expressed in distinct domains within the flower. The link between the two classes of genes has remained unknown so far. Here we show that the meristem-identity gene LEAFY has a role in controlling homeotic genes that is separable from its role in specifying floral fate. On the basis of our observation that LEAFY activates different homeotic genes through distinct mechanisms, we propose a genetic framework for the control of floral patterning.

AGAMOUS Protein, Arabidopsis↗
PubMed1998

Patterning the floral meristem.

Flowers are reproductive structures unique to the angiosperms. Flowers, which develop from small mounds of cells called floral meristems, show a number of universal patterns such as the arrangement of organs of different type along the floral axis. However, other conserved patterns, such as floral asymmetry, are merely conserved within different subgroups. This review discusses the emerging picture of early operating developmental mechanisms, which pattern floral meristems along the radial and dorsiventral axes, and of later-acting ones, which pattern tissue differentiation within floral organs.

Body Patterning↗
PubMed1998

Genetic ablation of flowers in transgenic Arabidopsis.

We have created transgenic Arabidopsis plants in which a gene encoding the cell-autonomous diphtheria toxin A chain (DT-A) was expressed under the control of the LEAFY (LFY) promoter. This promoter is active both in emerging leaf primordia and young flowers, with the highest activity in flowers. The majority of LFY::DT-A plants had normal vegetative development but lacked flowers, demonstrating that relatively widespread activity of a promoter does not exclude its possible use for ablating selected tissues, as long as differences in activity levels between different tissues are significant. We also found that flowers were replaced by empty bracts in LFY::DT-A plants, suggesting that flower-derived signals normally suppress bract development in Arabidopsis.

Arabidopsis↗
PubMed1998

Flowering-time genes modulate the response to LEAFY activity.

Among the genes that control the transition to flowering in Arabidopsis is a large group whose inactivation causes a delay in flowering. It has been difficult to establish different pathways in which the flowering-time genes might act, because mutants with lesions in these genes have very similar phenotypes. Among the putative targets of the flowering-time genes is another group of genes, which control the identity of individual meristems. Overexpression of one of the meristem-identity genes, LEAFY, can cause the precocious generation of flowers and thus early flowering. We have exploited the opposite phenotypes seen in late-flowering mutants and LEAFY overexpressers to clarify the genetic interactions between flowering-time genes and LEAFY. According to epistatic relationships, we can define one class of flowering-time genes that affects primarily the response to LEAFY activity, and another class of genes that affects primarily the transcriptional induction of LEAFY. These observations allow us to expand previously proposed models for the genetic control of flowering time.

Arabidopsis Proteins↗
PubMed1998

Gibberellins promote flowering of arabidopsis by activating the LEAFY promoter

The gibberellin class of plant hormones has been implicated in the control of flowering in several species. In Arabidopsis, severe reduction of endogenous gibberellins delays flowering in long days and prevents flowering in short days. We have investigated how the differential effects of gibberellins on flowering correlate with expression of LEAFY, a floral meristem identity gene. We have found that the failure of gibberellin-deficient ga1-3 mutants to flower in short days was paralleled by the absence of LEAFY promoter induction. A causal connection between these two events was confirmed by the ability of a constitutively expressed LEAFY transgene to restore flowering to ga1-3 mutants in short days. In contrast to short days, impairment of gibberellin biosynthesis caused merely a reduction of LEAFY expression when plants were grown in long days or with sucrose in the dark. As a first step toward identifying other small molecules that might regulate flowering, we have developed a rapid in vitro assay for LEAFY promoter activity.

Journal Article↗
PubMed1997

Flower development: repressing reproduction.

The homeotic genes that determine floral organ identity in plants turn out to be regulated by trans-acting factors related to the Polycomb-group proteins that have long been known as regulators of homeotic gene expression in Drosophila.

Animals↗
PubMed1997

Modulating the timing of flowering.

Several genes that are normally involved in flower initiation have recently been shown to induce early flowering when expressed ectopically in transgenic plants. These findings permit the development of strategies for the rational manipulation of flowering time in agronomically important plants.

Journal Article↗
PubMed1997

A LEAFY co-regulator encoded by UNUSUAL FLORAL ORGANS.

BACKGROUND: . Development of petals and stamens in Arabidopsis flowers requires the function of the organ-identity gene APETALA3 (AP3), whose RNA is expressed specifically in petal and stamen primordia. AP3 expression is positively regulated by the meristem-identity gene LEAFY (LFY), which is expressed ubiquitously in young flowers. It is unknown how the transition from ubiquitous expression of LFY to region-specific expression of AP3 is made. It has previously been proposed for Antirrhinum that another gene, FIMBRIATA (FIM), mediates between the LFY and AP3 orthologs, with the three genes acting in a simple regulatory hierarchy. FIM is activated later than the LFY ortholog, and its expression is more restricted than that of the LFY ortholog. RESULTS: . We have tested whether the model proposed for Antirrhinum applies to Arabidopsis, by creating transgenic plants in which the FIM ortholog UNUSUAL FLORAL ORGANS (UFO) was expressed constitutively from the promoter of the cauliflower mosaic virus 35S gene. In 35S::UFO flowers, AP3 was expressed precociously and ectopically, confirming that UFO is an upstream regulator of AP3. However, 35S::UFO could not restore petal and stamen development in lfy mutants, indicating that UFO can only function in the presence of LFY activity. The failure of 35S::UFO to rescue lfy mutants is consistent with our observation that UFO expression levels are not markedly changed in lfy mutants. CONCLUSIONS: . We conclude that UFO is not a simple mediator between meristem- and organ-identity genes, but is likely to be a partially dispensable co-regulator that acts together with LFY. The interplay between LFY and UFO provides a paradigm for how a global regulator such as LFY activates selected target genes only in restricted regions within its expression domain.

Arabidopsis↗
PubMed1997

Exfoliative cheilitis (EC) in AIDS: association with Candida infection.

Forty-seven of 165 patients with AIDS (28.5%) showed exfoliative cheilitis (EC), predominantly of the lower lip (n = 37). Histologically, hyphae were revealed in 23 of 47 cases (49%). In 14 of 23 specimens the histological and microbiological findings were in accordance. Smears of the vermilion border revealed Candida albicans in half of the cases (51%); however, combinations with C. krusei, C. tropicalis and C. glabrata were also seen. Twenty of 35 patients given fluconazole either prophylactically or therapeutically showed clinical signs of oral candidiasis. Frequent moistening of the lips may result in infection of the vermilion border with Candida species; consequent desiccation of the lips will lead to scale formation and exfoliation. Smears of the vermilion border of the lower lip of 20 controls with AIDS were positive in four cases. Twenty HIV-negative controls without EC showed negative microbiological results for Candida species. Exfoliative cheilitis may be associated with Candida infection in some cases and may be considered another variant of candidiasis in AIDS patients.

AIDS-Related Opportunistic Infections↗
PubMed1997

LEAFY expression and flower initiation in Arabidopsis.

During the initial vegetative phase, the Arabidopsis shoot meristem produces leaves with associated lateral shoots at its flanks, while the later reproductive phase is characterized by the formation of flowers. The LEAFY gene is an important element of the transition from the vegetative to the reproductive phase, as LEAFY is both necessary and sufficient for the initiation of individual flowers. We have analyzed in detail the expression of LEAFY during the plant life cycle, and found that LEAFY is extensively expressed during the vegetative phase. In long days, Arabidopsis plants flower soon after germination, and this is paralleled by rapid upregulation of LEAFY. In short days, Arabidopsis plants flower several weeks later than in long days, but LEAFY expression increases gradually before flowering commences. Application of the plant hormone gibberellin, which hastens flowering in short days, enhances the gradual change in LEAFY expression observed in short days. Changes in LEAFY expression before the transition to flowering suggest that the time point of this transition is at least partly controlled by the levels of LEAFY activity that are prevalent at a given time of the life cycle. This assumption is borne out by the finding that increasing the copy number of endogenous LEAFY reduces the number of leaves produced before the first flower is formed. Thus, LEAFY combines properties of flowering-time and flower-meristem-identity genes, indicating that LEAFY is a direct link between the global process of floral induction and the regional events associated with the initiation of individual flowers.

Arabidopsis↗
PubMed1997

Floral determination and expression of floral regulatory genes in Arabidopsis.

The expression of the floral regulators LEAFY, APETALA1 and AGAMOUS-LIKE8 was examined during light treatments that induced flowering in Arabidopsis, and was compared to time points at which floral determination occurred. Extension of an 8-hour day by either continuous red- or far-red-enriched light induced LEAFY and AGAMOUS-LIKE8 expression within 4 hours. The 4 hours of additional light was sufficient for floral determination only in the far-red-enriched conditions, while 12-16 hours of additional light was required for floral determination in the red-enriched conditions. These results indicate that the induction of floral regulatory genes and induction of flower formation can be uncoupled under certain circumstances. Expression of LEAFY and AGAMOUS-LIKE8 in the shoot apex at the time of floral determination is also consistent with genetic data indicating that these genes are involved in the first steps of the transition from vegetative to reproductive development. In contrast to LEAFY and AGAMOUS-LIKE8, APETALA1 expression was first observed 16 hours after the start of photoinduction. Since this time point was always after floral determination, APETALA1 is an indicator of floral determination.

Arabidopsis↗
PubMed1995

A developmental switch sufficient for flower initiation in diverse plants.

We have generated transgenic plants in which the flower-meristem-identity gene LEAFY of Arabidopsis is constitutively expressed. LEAFY is sufficient to determine floral fate in lateral shoot meristems of both Arabidopsis and the heterologous species aspen, with the consequence that flower development is induced precociously. Our results also suggest a new level of regulation during flower development, as indicated by the competence of the main shoot to respond to LEAFY activity.

Arabidopsis↗
PubMed1995

The genetics of flower development: from floral induction to ovule morphogenesis.

Flower development consists of several phases. The first step is the transition from vegetative to reproductive development, regulated by floral induction. Later steps include the initiation of individual flowers, the determination of organ identity, and organ-specific differentiation. One of the major discoveries of plant biology is that the genetic network controlling flower development is highly conserved in two distantly related dicots, Arabidopsis thaliana and Antirrhinum majus, and probably in other species as well. Classical genetics has identified a sizable number of genes regulating flower development, and many of these regulatory genes have been cloned. This review summarizes recent advances in the understanding of the genetic control of floral induction and determination of flower-meristem identity, with the focus on Arabidopsis thaliana. In addition, recent work on ovule morphogenesis, a late process in flower development, is discussed.

Arabidopsis↗