The mechanics of cell fate determination in petals. (1/76)

The epidermal cells of petals of many species are specialized, having a pronounced conical shape. A transcription factor, MIXTA, is required for the formation of conical cells in Antirrhinum majus; in shoot epidermal cells of several species, expression of this gene is necessary and sufficient to promote conical cell formation. Ectopic expression has also shown MIXTA to be able to promote the formation of multicellular trichomes, indicating that conical cells and multicellular trichomes share elements of a common developmental pathway. Formation of conical cells or trichomes is also mutually exclusive with stomatal formation. In Antirrhinum, MIXTA normally only promotes conical cell formation on the inner epidermal layer of the petals. Its restricted action in cell fate determination results from its specific expression pattern. Expression of MIXTA, in turn, requires the activity of B-function genes, and biochemical evidence suggests that the products of DEFICIENS, GLOBOSA and SEPALLATA-related genes directly activate MIXTA expression late in petal development, after the completion of cell division in the petal epidermis. A MIXTA-like gene, AmMYBML1, is also expressed in petals. AmMYBML1 expression is high early in petal development. This gene may direct the formation of trichomes in petals. In specifying the fates of different cell types in petals, regulatory genes like MIXTA may have been duplicated. Changes in the timing and spatial localization of expression then provides similar regulatory genes which specify different cell fates.  (+info)

Evidence for cytoplasmic inheritance of a developmental organizer affecting growth habit and leaf shape in Antirrhinum majus. (2/76)

A cross between two distinct, true-breeding plants of Antirrhinum majus L. showed an unexpected pattern of inheritance of growth habit in the F2, which was extended to both growth habit and leaf shape in the F3 generation of all the plants traced further. All the F3 families, offspring of individual F2 plants, were very uniform for both growth habit and leaf shape traits but differed distinctly from each other in these respects. The backcrosses of selected F3 and F4 families to the original parents in the cross did not segregate for the distinctive family phenotypes. This led to the postulate that a cytoplasmic factor was involved in the regulation and/or integration of genetic information concerned with growth habit/leaf shape. The similarity of the reciprocal backcrosses of the F3 and F4 families led to the further postulate that the proposed cytoplasmic factor was specified by both the maternal and paternal parents to a similar degree. That the gene component was segregating normally was shown by the inheritance of four marker genes for flower colour, colour pattern and flower shape.  (+info)

Polymorphic microsatellites in Antirrhinum (Scrophulariaceae), a genus with low levels of nuclear sequence variability. (3/76)

In Antirrhinum, reproductive systems range from self-compatible to self-incompatible, but the actual outcrossing rates of self-compatible populations are not known. Thus the extent to which levels of variability and inbreeding differ among Antirrhinum populations is not known. In order to address this issue we isolated nine Antirrhinum nuclear microsatellite loci. In contrast to several nuclear genes that show low levels of sequence variation, six of the microsatellite loci indicate high levels of variability within and between Antirrhinum species. The highly self-compatible Antirrhinum majus ssp. cirrhigerum population has high levels of variability and no significant deviation from Hardy-Weinberg equilibrium, suggesting substantial rates of outcrossing.  (+info)

Genetic variability in a narrow endemic snapdragon (Antirrhinum subbaeticum, Scrophulariaceae) using RAPD markers. (4/76)

Antirrhinum subbaeticum is an endangered species inhabiting fragmented limestone cliffs. In the last 3 years, a drastic population decline has been observed in three of four known populations and the estimated number of surviving individuals is now close to 400. A RAPD study was conducted to evaluate the levels of genetic variation present in this species to improve conservation guidelines. Thirty-nine polymorphic products identified 66.1% of the samples by unique RAPD multilocus profiles. A cluster analysis grouped the samples into two broad groups corresponding to northern or southern provenances. AMOVA analysis showed that only 17.7% of the genetic diversity was partitioned within populations. These results are in contrast to data available for other Antirrhinum species. This genetic structure could be explained by the predominant selfing behaviour exhibited by A. subbaeticum as opposed to the allogamy of other congeners. Genetic diversity within populations does not seem to be strongly related to population size and historical factors could be responsible for the very low levels of genetic diversity found in one population. Given the low genetic diversity within populations, it is suggested that an extensive sampling of individuals be made for recovering appropriate levels of the gene pool for ex situ preservation. However, translocation of individuals to the genetically weakened Bogarra population from other sources is not recommended.  (+info)

AhSL28, a senescence- and phosphate starvation-induced S-like RNase gene in Antirrhinum. (5/76)

Several species of higher plants have been found to contain S-like ribonucleases (RNases), which are homologous to S-RNases controlling self-incompatibility. No S-like RNase genes have been isolated from self-incompatible Antirrhinum. To investigate the relationship between S- and S-like RNases, we cloned a gene named AhSL28 encoding an S-like RNase in Antirrhinum. Amino acid sequence, genomic structure and phylogenetic analyses indicated that AhSL28 is most similar to RNS2, an S-like RNase from Arabidopsis thaliana and formed a distinct subclass together with several other S-like RNases within the S-RNase superfamily. Unlike S-RNase genes in Antirrhinum, AhSL28 is not only expressed in pistils but also in leaves, petals, sepals and anthers, in particular, showing a strong expression in vascular tissues and transmitting track. Moreover, its RNA transcripts were induced during leaf senescence and phosphate (Pi) starvation but not by wounding, indicating that AhSL28 plays a role in remobilizing Pi and other nutrients, particularly when cells senesce and are under limited Pi conditions in Antirrhinum. Possible evolutionary relations of S- and S-like RNases as well as signal transduction pathways related to S-like RNase action are discussed.  (+info)

Separation of genetic functions controlling organ identity in flowers. (6/76)

Comparative studies on the ABC model of floral development have revealed extensive conservation of B and C class genes, but have failed to identify similar conservation for A class genes. Using a reverse genetic approach, we show that the previous inability to obtain Antirrhinum mutants corresponding to the A class gene AP2 of Arabidopsis reflects greater genetic redundancy in Antirrhinum . Antirrhinum has two genes corresponding to AP2, termed LIP1 and LIP2, both of which need to be inactivated to give a mutant phenotype. Analysis of interactions between LIP and class B/C genes shows that unlike AP2 in Arabidopsis, LIP genes are not required for repression of C in outer whorls of the flower. However, like AP2, LIP genes play a role in sepal, petal and ovule development, although some of their detailed effects are different, reflecting the diverse morphologies of Antirrhinum and Arabidopsis flowers. The dual functions for which AP2 is required in Arabidopsis are therefore separate in Antirrhinum, showing that the genetic basis of some aspects of organ identity have undergone major evolutionary change.  (+info)

Genetic control of surface curvature. (7/76)

Although curvature of biological surfaces has been considered from mathematical and biophysical perspectives, its molecular and developmental basis is unclear. We have studied the cin mutant of Antirrhinum, which has crinkly rather than flat leaves. Leaves of cin display excess growth in marginal regions, resulting in a gradual introduction of negative curvature during development. This reflects a change in the shape and the progression of a cell-cycle arrest front moving from the leaf tip toward the base. CIN encodes a TCP protein and is expressed downstream of the arrest front. We propose that CIN promotes zero curvature (flatness) by making cells more sensitive to an arrest signal, particularly in marginal regions.  (+info)

A linkage map of an F2 hybrid population of Antirrhinum majus and A. molle. (8/76)

To increase the utility of Antirrhinum for genetic and evolutionary studies, we constructed a molecular linkage map for an interspecific hybrid A. majus x A. molle. An F(2) population (n = 92) was genotyped at a minimum of 243 individual loci. Although distorted transmission ratios were observed at marker loci throughout the genome, a mapping strategy based on a fixed framework of codominant markers allowed the loci to be placed into eight robust linkage groups consistent with the haploid chromosome number of Antirrhinum. The mapped loci included 164 protein-coding genes and a similar number of unknown sequences mapped as AFLP, RFLP, ISTR, and ISSR markers. Inclusion of sequences from mutant loci allowed provisional alignment of classical and molecular linkage groups. The total map length was 613 cM with an average interval of 2.5 cM, but most of the loci were aggregated into clusters reducing the effective distance between markers. Potential causes of transmission ratio distortion and its effects on map construction were investigated. This first molecular linkage map for Antirrhinum should facilitate further mapping of mutations, major QTL, and other coding sequences in this model genus.  (+info)