THE BELL1 GENE ENCODES A HOMEODOMAIN PROTEIN INVOLVED IN PATTERN-FORMATION IN THE ARABIDOPSIS OVULE PRIMORDIUM

Ovule development in Arabidopsis involves the formation of three morph ologically defined proximal-distal pattern elements. Integuments arise from the central pattern element. Analysis of Bell1 (Bel1) mutant ovu les indicated that BEL1 was required for integument development, Cloni ng of the BEL1 locus reveals that it encodes a homeodomain transcripti on factor. Prior to integument initiation, BEL1 RNA localizes to the c entral domain, providing molecular evidence for a central pattern elem ent. Therefore, proximal-distal patterning of the ovule involves the r egulated expression of the BEL1 gene that controls integument morphoge nesis. A model for BEL1 function is evaluated with regard to new data showing the expression pattern of the floral homeotic gene AGAMOUS (AG ) early in wild-type and Bel1 ovule development.