9505813 Fischer The ovule is a fundamental unit of plant reproduction that generates the female gametophyte, mediates fertilization processes, and support the development of the embryo. The long term goal of this proposal is to understand the genetic circuits that control the early development of the ovule by analyzing two Arabidopsis genes, BELL1 (BEL1) and OVULE MUTATION2 (OVM2), that were cloned in Dr. Fischer's laboratory. The BEL1 gene product plays a role in the specification of ovule identity. bel1 mutant ovules are often transformed into carpel like structures, isolation and sequencing of the BEL1 gene indicates that it encodes a homeodomain transcription factor. It is thought that the BEL1 gene prevents the carpel developmental program from over-riding ovule development by negatively regulating expression of the floral homeotic gene, AGAMOUS(AG). The OVM2 gene product is needed at distinct threshold levels to control ovule and female gametophyte development, respectively. With no active OVM2 protein, both ovule and female gametophyte development are dramatically suppressed, whereas a low level of OVM2 protein results in nonfunctional ovules that specifically lack a female gametophyte. Isolation and sequencing of the OVM2 gene indicates that it is related to the floral homeotic gene APETALA2 (AP2). Thus, BEL1 and OVM2 genes are important regulators of ovule and female gametophyte development, with mutations resultilg in homeotic conversions and deletions of organs. To understand their mechanism of action, the critical steps that control early ovule development, and the relationship between ovule and floral developmental programs, experiments will be carried out to: 1) Determine the temporal and spatial localization of BEL1 and OVM2 activity, 2) Determine the genetic relationships between ovule and floral regulatory genes, 3) Carry out a molecular analysis of BEL1 and OVM2 function, and 4) Carry out a genetic screen to identify new genes that control megagametogenesis. ***
