ABSTRACT
Organ asymmetry is thought to have evolved many times independently in plants. In Antirrhinum, asymmetry of the flower and its component organs requires cyc and dich gene activity. We show that, like cyc, the dich gene encodes a product belonging to the TCP family of DNA-binding proteins that is first expressed in the dorsal domain of early floral meristems. However, whereas cyc continues to be expressed throughout dorsal regions, expression of dich eventually becomes restricted to the most dorsal half of each dorsal petal. This correlates with the effects of dich mutations and ectopic cyc expression on petal shape, providing an indication that plant organ asymmetry can reflect subdomains of gene activity. Taken together, the results indicate that plant organ asymmetry can arise through a series of steps during which early asymmetry in the developing meristem is progressively built upon.
Subject(s)
Plant Proteins/physiology , Plant Structures/physiology , Amino Acid Sequence , Base Sequence , DNA Transposable Elements , DNA, Plant , Molecular Sequence Data , Mutagenesis, Insertional , Mutation , Phenotype , Plant Physiological Phenomena , Plant Proteins/biosynthesis , Plant Proteins/genetics , Plant Proteins/isolation & purification , Sequence Homology, Amino AcidABSTRACT
Dorsoventral asymmetry in flowers is thought to have evolved many times from a radially symmetrical ancestral condition. The first gene controlling floral asymmetry, cycloidea in Antirrhinum, has been isolated. The cycloidea gene is expressed at a very early stage in dorsal regions of floral meristems, where it affects growth rate and primordium initiation. Expression continues through to later stages in dorsal primordia to affect the asymmetry, size and cell types of petals and stamens.
Subject(s)
Plant Proteins/genetics , Plants/genetics , Alleles , Amino Acid Sequence , Base Sequence , DNA, Plant , DNA-Binding Proteins , Molecular Sequence Data , Mutation , Phenotype , Plants/anatomy & histology , Transcription FactorsABSTRACT
Flowering plants exhibit two types of inflorescence architecture: determinate and indeterminate. The centroradialis mutation causes the normally indeterminate inflorescence of Antirrhinum to terminate in a flower. We show that centroradialis is expressed in the inflorescence apex a few days after floral induction, and interacts with the floral-meristem-identity gene floricaula to regulate flower position and morphology. The protein CEN is similar to animal proteins that associate with lipids and GTP-binding proteins. We propose a model for how different inflorescence structures may arise through the action and evolution of centroradialis.
Subject(s)
Androgen-Binding Protein , Carrier Proteins , Plant Proteins/genetics , Plants/genetics , Amino Acid Sequence , Base Sequence , Carrier Proteins/chemistry , Carrier Proteins/metabolism , DNA, Plant , GTP-Binding Proteins/chemistry , Gene Expression Regulation, Plant , Genes, Plant , Molecular Sequence Data , Mutation , Phosphatidylcholines/metabolism , Phospholipid Transfer Proteins , Plant Development , Plant Proteins/chemistry , Plant Proteins/metabolismABSTRACT
The flower meristem identity genes floricaula (flo) and squamosa (squa) promote a change in phyllotaxy from spiral to whorled in Antirrhinum. To determine how this might be achieved, we have performed a combination of morphological, genetic, and expression analyses. Comparison of the phenotypes and RNA expression patterns of single and double mutants with the wild type showed that flo and squa act together to promote flower development but that flo is epistatic to squa with respect to early effects on phyllotaxy. We propose that a common process underlies the phyllotaxy of wildtype, flo, and squa meristem development but that the relative timing of primordium initiation or growth is altered. This process depends on two separable events: setting aside zones for potential primordium initiation and partitioning these zones into discrete primordia. Failure of the second event can lead to the formation of continuous double spirals, which are occasionally seen in flo mutants.