XVI International Botanical Congess

Studies on higher eudicots have led to the development of the ABC model of floral organ identity determination. The model assumes that sepal identity is specified by the floral homeotic A function, petal identity by A+B, stamen identity by B+C, and carpel identity by C. The flowers of many angiosperms however, have an architecture which is different from that of the typical higher eudicot flower. Lily species, for example, have petaloid tepals rather than distinct sepals and petals in their first two floral whorls. To find out how the ABC model has to be modified for the Liliaceae, we have cloned and characterized orthologs of A, B and C function genes from Lilium regale. Our data suggest that that petaloid character of the outer floral organs in lily is due to the Aectopic@ expression of B class floral homeotic genes in the organs of the 1st whorl of the flower. Thus with respect to the spatial aspect of homeotic gene expression, lily spells the floral ABC a bit different from the higher eudicots.