GENETIC SEPARATION OF 3RD AND 4TH WHORL FUNCTIONS OF AGAMOUS

AGAMOUS (AG) is an Arabidopsis MADS box gene required for normal devel opment of the third and fourth whorls of the flower. In previously des cribed ag mutants, the third whorl stamens are replaced by petals, and the fourth whorl is replaced by another (mutant) flower. We describe two new ag alleles, ag-4 and AG-Met205, retaining partial AG activity. Both produce flowers with stamens in the third whorl and indeterminat e floral meristems; however, ag-4 flowers contain sepals in the fourth whorl, and AG-Met205 produces carpels. The ag-4 mutation results in p artial loss of the C terminus of the K domain, a putative coiled coil, and AG-Met205 contains a site-directed mutation that causes a single amino acid change in this same region of the K box. Two models that mi ght explain how these changes in AG result in the separation of differ ent AG activities are discussed.