BELL1 and AGAMOUS genes promote ovule identity in Arabidopsis thaliana

Molecular and genetic analyses have demonstrated that the Arabidopsis thali ana gene BELL1 (BEL1) is required for proper morphogenesis of the ovule int eguments. Several lines of evidence suggest that BEL1 may act, at least in part, to repress the function of the organ identity gene AGAMOUS (AG) durin g ovule development. To study the relative roles of BEL1 and AG, plants hom ozygous for ag, bell or both were constructed in an ap2 mutant background w here ovules form even in the absence of AG function. The loss of either BEL 1 or AG led to a decrease in the number of mature ovules, accompanied by an increase in primordial outgrowths. These data suggest that BEL1 and AG gen e products act early in ovule development in a partially redundant manner t o direct ovule identity. Development of the abnormal integuments characteri stic of the Bel1(-) mutant phenotype was found to be dependent on AG functi on. Finally, BEL1 appears to be required for embryo sac development indepen dent of both other aspects of ovule morphogenesis and AG function. This stu dy therefore suggests that both BEL1 and AG are required for several distin ct aspects of ovule morphogenesis.