A role for flavin monooxygenase-like enzymes in auxin biosynthesis.

Although auxin is known to regulate many processes in plant development and has been studied for over a century, the mechanisms whereby plants produce it have remained elusive. Here we report the characterization of a dominant Arabidopsis mutant, yucca, which contains elevated levels of free auxin. YUCCA encodes a flavin monooxygenase-like enzyme and belongs to a family that includes at least nine other homologous Arabidopsis genes, a subset of which appears to have redundant functions.

Natural variation in phytochrome signaling.

The phytochromes, photoreceptors sensitive to red and far-red light, are critical for sensing foliage shade, canopy breaks, and neighbor proximity. A combination of molecular genetic, evolutionary, and ecological techniques are being used to understand how phytochromes function in the natural environment. We discuss studies on the adaptive value of phytochrome mediated plasticity, as well as the role that variation in phytochrome expression and function might play in allowing plants to adapt to unique light environments.

Transformation of rice with the Arabidopsis floral regulator LEAFY causes early heading.

Onset of flowering, or heading date, is an important agronomic trait of cereal crops such as rice and early-heading varieties are required for certain regions in which rice is cultivated. Since the floral control gene LEAFY from Arabidopsis can dramatically accelerate flowering in dictoyledonous plants, the usefulness of LEAFY for manipulating heading date in rice has been tested. Constitutive expression of LEAFY from the cauliflower mosaic virus 35S promoter caused early flowering in transgenic rice, with a heading date that was 26-34 days earlier than that of wild-type plants.

Report of a Subcommittee on the Nomenclature of n-Dimensional Crystallography. I. Symbols for point-group transformations, families, systems and geometric crystal classes.

The notation of crystallography in arbitrary dimensions is considered. Recommended symbols for point-group transformations, geometric crystal classes, families and systems are presented.

Cell-cell signaling and movement by the floral transcription factors LEAFY and APETALA1.

LEAFY (LFY) and APETALA1 (AP1) encode unrelated transcription factors that activate overlapping sets of homeotic genes in Arabidopsis flowers. Sector analysis and targeted expression in transgenic plants were used to study whether LFY and AP1 can participate in cell-cell signaling between and within different layers of the floral meristem. LFY signaled equally well from all layers and had substantial long-range action within layers.

Transformation of Medicago truncatula via infiltration of seedlings or flowering plants with Agrobacterium.

Two rapid and simple in planta transformation methods have been developed for the model legume Medicago truncatula. The first approach is based on a method developed for transformation of Arabidopsis thaliana and involves infiltration of flowering plants with a suspension of Agrobacterium. The second method involves infiltration of young seedlings with Agrobacterium.

Integration of floral inductive signals in Arabidopsis.

Flowering of Arabidopsis is regulated by a daylength-dependent pathway that accelerates flowering in long days and a daylength-independent pathway that ensures flowering in the absence of inductive conditions. These pathways are genetically separable, as there are mutations that delay flowering in long but not short days. Conversely, mutations that block synthesis of the hormone gibberellin abolish flowering in short days, but have on their own only a minor effect in long days.

Activation tagging in Arabidopsis.

Activation tagging using T-DNA vectors that contain multimerized transcriptional enhancers from the cauliflower mosaic virus (CaMV) 35S gene has been applied to Arabidopsis plants. New activation-tagging vectors that confer resistance to the antibiotic kanamycin or the herbicide glufosinate have been used to generate several tens of thousands of transformed plants. From these, over 30 dominant mutants with various phenotypes have been isolated.

Regulation of auxin response by the protein kinase PINOID.

Arabidopsis plants carrying mutations in the PINOID (PID) gene have a pleiotropic shoot phenotype that mimics that of plants grown on auxin transport inhibitors or of plants mutant for the auxin efflux carrier PINFORMED (PIN), with defects in the formation of cotyledons, flowers, and floral organs. We have cloned PID and find that it is transiently expressed in the embryo and in initiating floral anlagen, demonstrating a specific role for PID in promoting primordium development. Constitutive expression of PID causes a phenotype in both shoots and roots that is similar to that of auxin-insensitive plants, implying that PID, which encodes a serine-threonine protein kinase, negatively regulates auxin signaling.

[Problem-based learning (POL) in environmental medicine].

"Environmental medicine" is a new sub-discipline in the spectrum of medical specialization in Germany. The Berlin Academy of Occupational Medicine and Health Protection, now a branch of the Berlin Chamber of Physicians, developed a 200-lesson curriculum for physicians who want to specialize in this field. Coincidentally during the initial courses, the attendants were already highly qualified ("Facharzt"-level) and experts in various occupational fields, and hence the composition of the classes was highly heterogeneous on the levels of practical experience as well as theoretical knowledge.

Redundant enhancers mediate transcriptional repression of AGAMOUS by APETALA2.

The floral homeotic gene AGAMOUS specifies stamen and carpel fate in the central whorls of Arabidopsis flowers. Transcription of AGAMOUS RNA is restricted to the center of developing flowers by several, partially redundant negative regulators, one of which is the homeotic gene APETALA2. We have identified regulatory elements that mediate transcriptional repression of AGAMOUS by APETALA2 and found that several redundant elements respond independently to loss of APETALA2 activity.

Activation tagging of the floral inducer FT.

FLOWERING LOCUS T (FT), which acts in parallel with the meristem-identity gene LEAFY (LFY) to induce flowering of Arabidopsis, was isolated by activation tagging. Like LFY, FT acts partially downstream of CONSTANS (CO), which promotes flowering in response to long days. Unlike many other floral regulators, the deduced sequence of the FT protein does not suggest that it directly controls transcription or transcript processing.

The Arabidopsis thaliana MERISTEM LAYER 1 promoter specifies epidermal expression in meristems and young primordia.

The Arabidopsis thaliana MERISTEM LAYER 1 (ATML1) gene is expressed in the epidermis of developing embryos and shoot meristems. To identify regulatory sequences necessary for epidermis-specific expression, three fusions of overlapping ATML1 genomic sequences to the GUS reporter gene were introduced into Arabidopsis plants. All fusion genes conferred epidermis-specific expression of both GUS mRNA and protein activity but varied in both the timing and relative levels of expression, suggesting partial redundancy of ATML1 regulatory elements.

Independent regulation of flowering by phytochrome B and gibberellins in Arabidopsis.

Phytochromes and gibberellins (GAs) coordinately regulate multiple aspects of Arabidopsis development. Phytochrome B (PHYB) promotes seed germination by increasing GA biosynthesis, but inhibits hypocotyl elongation by decreasing the responsiveness to GAs. Later in the life cycle of the plant, PHYB and GAs have opposite effects on flowering.

Activation of a floral homeotic gene in Arabidopsis.

The patterned expression of floral homeotic genes in Arabidopsis depends on the earlier action of meristem-identity genes such as LEAFY, which encodes a transcription factor that determines whether a meristem will generate flowers instead of leaves and shoots. The LEAFY protein, which is expressed throughout the flower, participates in the activation of homeotic genes, which are expressed in specific regions of the flower. Analysis of a LEAFY-responsive enhancer in the homeotic gene AGAMOUS indicates that direct interaction of LEAFY with this enhancer is required for its activity in plants.

The Arabidopsis flowering-time gene LUMINIDEPENDENS is expressed primarily in regions of cell proliferation and encodes a nuclear protein that regulates LEAFY expression.

Mutations in the LUMINIDEPENDENS (LD) gene of Arabidopsis thaliana (L.) Heynh. (Arabidopsis) confer a late-flowering phenotype, indicating that LD normally functions to promote the floral transition.

From floral induction to floral shape.

The initial emphasis in molecular-genetic studies of flower development was on homeotic genes that control organ identity, which is rather invariant between different species. Studies in flower development during the past three years have dealt with more diverse aspects of flower development, including floral induction and floral shape. Genes identified in the respective pathways might hold clues to the diversity of modern angiosperms.

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.

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.

Plant development: the making of a leaf.

A transcription factor of the Myb family has been found to couple dorsoventral patterning and proximodistal outgrowth during leaf development.

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.

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.