A molecular recombination map of Antirrhinum majus.

Background: Genetic recombination maps provide important frameworks for comparative genomics, identifying gene functions, assembling genome sequences and for breeding. The molecular recombination map currently available for the model eudicot Antirrhinum majus is the result of a cross with Antirrhinum molle, limiting its usefulness within A. majus.

Tracing the evolution of the floral homeotic B- and C-function genes through genome synteny.

The evolution of the floral homeotic genes has been characterized using phylogenetic and functional studies. It is possible to enhance these studies by comparing gene content and order between species to determine the evolutionary history of the regulatory genes. Here, we use a synteny-based approach to trace the evolution of the floral B- and C-function genes that are required for specification of the reproductive organs.

Floral organ identity: 20 years of ABCs.

One of the early successes of the application of molecular genetics to study plant development was the discovery of a series of genes that act together, in an apparently simple combinatorial model, to specify the identity of the different organs of a flower. Widely known as the ABC model, this framework for understanding has been investigated and modified over the course of the last two decades. The cast list of genes has been defined and, as other chapters in this volume will show, great progress has been made in understanding how they are regulated, how they act together, what they do and how they have contributed to the evolution of the flower in its varied forms.

Enhanced AGAMOUS expression in the centre of the Arabidopsis flower causes ectopic expression over its outer expression boundaries.

Spatial regulation of C-function genes controlling reproductive organ identity in the centre of the flower can be achieved by adjusting the level of their expression within the genuine central expression domain in Antirrhinum and Petunia. Loss of this control in mutants is revealed by enhanced C-gene expression in the centre and by lateral expansion of the C-domain. In order to test whether the level of central C-gene expression and hence the principle of 'regulation by tuning' also applies to spatial regulation of the C-function gene AGAMOUS (AG) in Arabidopsis, we generated transgenic plants with enhanced central AG expression by using stem cell-specific CLAVATA3 (CLV3) regulatory sequences to drive transcription of the AG cDNA.

A conserved microRNA module exerts homeotic control over Petunia hybrida and Antirrhinum majus floral organ identity.

It is commonly thought that deep phylogenetic conservation of plant microRNAs (miRNAs) and their targets indicates conserved regulatory functions. We show that the blind (bl) mutant of Petunia hybrida and the fistulata (fis) mutant of Antirrhinum majus, which have similar homeotic phenotypes, are recessive alleles of two homologous miRNA-encoding genes. The BL and FIS genes control the spatial restriction of homeotic class C genes to the inner floral whorls, but their ubiquitous early floral expression patterns are in contradiction with a potential role in patterning C gene expression.