MUTATIONS IN THE PERIANTHIA GENE OF ARABIDOPSIS SPECIFICALLY ALTER FLORAL ORGAN NUMBER AND INITIATION PATTERN

An open question in developmental biology is how groups of dividing ce lls can generate specific numbers of segments or organs, We describe t he phenotypic effects of mutations in PERIANTHIA, a gene specifically required for floral organ patterning in Arabidopsis thaliana. Most wil d-type Arabidopsis flowers have 4 sepals, 4 petals, 6 stamens, and 2 c arpels, Flowers of perianthia mutant plants most commonly show a penta merous pattern of 5 sepals, 5 petals, 5 stamens, and 2 carpels. This p attern is characteristic of flowers in a number of plant families, but not in the family Brassicaceae, which includes Arabidopsis, Unlike pr eviously described mutations affecting floral organ number, perianthia does not appear to affect apical or floral meristem sizes, nor is any other aspect of vegetative or floral development severely affected, F loral organs in perianthia arise in a regular, stereotypical pattern s imilar to that in distantly related species with pentamerous flowers, Genetic analysis shows that PERIANTHIA acts downstream of the floral m eristem identity genes and independently of the floral meristem size a nd floral organ identity genes in establishing floral organ initiation patterns, Thus PERIANTHIA acts in a previously unidentified process r equired for organ patterning in Arabidopsis powers.