ARABIDOPSIS FLORAL HOMEOTIC GENE BELL (BEL1) CONTROLS OVULE DEVELOPMENT THROUGH NEGATIVE REGULATION OF AGAMOUS GENE (AG)

Ovules are the developmental precursors of seeds. In angiosperms the o vules are enclosed within the central floral organs, the carpels. We h ave identified a homeotic mutation in Arabidopsis, ''bell'' (bell), wh ich causes transformation of ovule integuments into carpels, In situ h ybridization analysis shows that this mutation leads to increased expr ession of the carpel-determining homeotic gene AGAMOUS (AG) in the mut ant ovules. Introduction of a constitutively expressed AG transgene in to wild-type plants causes the ovules to resemble those of bell mutant s. We propose that the BEL1 gene product directs normal integument dev elopment, in part by suppressing AG expression in this structure. Our results allow expansion of the current model of floral organ identity to include regulation of ovule integument identity.