Floral homeotic gene expression defines developmental arrest stages inBrassica oleracea L. vars.botrytis anditalica

Abstract

Brassica oleracea L. vars.italica (broccoli) andbotrytis (cauliflower) both undergo developmental arrests which result in heading phenotypes. We characterized these arrested tissues at the morphological and molecular levels, and defined the developmental changes that ensue after arrest has been broken. We found that the order of floral organ initiation and the positions of resulting floral organ primordia in this species differed in some respects from that ofArabidopsis, which is a member of the same family, Brassicaceae. We also cloned homologs of theArabidopsis floral homeotic genesAPETALA1 (AP1) andAPETALA3 (AP3) fromB. oleracea and characterized their expression patterns. We found that theAP1 homolog was expressed in some of the meristems of arrest-stage cauliflower, providing evidence that this tissue is florally determined. In broccoli, both the API andAP3 homologs were expressed. However, the spatial pattern of expression of the broccoliAP1 homolog differed from that ofArabidopsis. In addition, we identified a homolog of theCAULIFLOWER (CAL) gene,BoiCAL, from broccoli. The predicted amino acid sequence indicated that theBoiCAL gene product does not contain the mutation thought to be responsible for the early arrest exhibited in cauliflower (Kempin et al. 1995), but contains other changes that might play a role in the broccoli heading phenotype.