Ovule development in Arabidopsis involves the formation of three morphologically defined proximal-distal pattern elements. Integuments arise from the central pattern element. Analysis of Bell1 (Bell) mutant ovules indicated that BEL1 was required for integument development. Cloning of the BEL1 locus reveals that it encodes a homeodomain transcription factor. Prior to integument initiation, BEL1 RNA localizes to the central domain, providing molecular evidence for a central pattern element. Therefore, proximal-distal patterning of the ovule involves the regulated expression of the BEL1 gene that controls integument morphogenesis. 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 Bell ovule development.
Bibliographical noteFunding Information:
We thank Chad Williams and Anita Ambegaokar for their excellent technical help. We thank Diane Jofuku for her invaluable assistance with the in situ hybridization and Steve Ruzin of the National Science Foundation Center for Plant Developmental Biology for advice and use of the equipment. We thank Gail McLean and John Zupan for plasmids and help with setting up the nuclear localization experiments, Dr. Judy Roe for her advice on cloning T-DNA-tagged mutants, and Jef Sheurinkof PlantGeneticSystemsforsequencing. Wearegrateful to the members of the Fischer and Hake labs forthe helpful discussions and to John Harada, Erik Vollbrecht, Sarah Hake, and Jack Okamuro for critical reading of this manuscript This work was funded by a National Science Foundation grant to R. L. F., a National Sciences and Engineering. Research Council of Canada research grant to G. W. H., and a Human Frontier Science Project Organization Long-Term Fellowship to N. 0.