EVOLUTION OF FLOWERS AND INFLORESCENCES

Plant development depends on the activity of meristems which continual ly reiterate a common plan. Permutations around this plan can give ris e to a wide range of morphologies. To understand the mechanisms underl ying this variation, the effects of parallel mutations in key developm ental genes are being studied in different species. In Antirrhinum, th ree of these key genes are: (1) floricaula (flo) a gene required for t he production of flowers (2) centroradialis (cen), a gene controlling flower position (3) cycloidea (eye), a gene controlling flower symmetr y, Several plant species, exhibiting a range of inflorescence types an d floral symmetries are being analysed in detail, Comparative genetic and molecular analysis shows that inflorescence architecture depends o n two underlying parameters: a basic inflorescence branching pattern a nd the positioning of flowers, The flo and cen genes play a key role i n the positioning of flowers, and variation in the site and timing of expression of these genes, may account for many of the different inflo rescence types. The evolution of inflorescence structure may also have influenced the evolution of floral asymmetry, as illustrated by the c en mutation which changes both inflorescence type and the symmetry of some flowers, Conflicting theories about the origins of irregular flow ers and how they have coevolved with inflorescence architecture can be directly assessed by examining the role of cyc- and cen-like genes in species displaying various floral symmetries and inflorescence types.