THE PLANT CELL, Vol 7, Issue 5 507-516, Copyright © 1995 by American Society of Plant Biologists
Functional Interaction between the Homeotic Genes fbp1 and pMADS1 during Petunia Floral Organogenesis
G. C. Angenent, M. Busscher, J. Franken, HJM. Dons and A. J. van Tunen
Department of Developmental Biology, DLO-Center for Plant Breeding and Reproduction Research (CPRO-DLO), P.O. Box 16, 6700 AA Wageningen, The Netherlands
The petunia MADS box floral binding protein (fbp) gene 1 represents a class
B homeotic gene determining the identity of second and third floral whorl
organs. Suppression of fbp1, which is highly homologous to the Antirrhinum
gene globosa and Arabidopsis gene pistillata, results in the conversion of
petals to sepals and stamens to carpels. In contrast to fbp1, the petunia
homeotic gene pMADS1, encoding a protein homologous to the Antirrhinum
protein DEFICIENS, has been shown to be involved in the formation of petals
only. We demonstrated that the induction of fbp1 is established independent
of pMADS1, whereas at later developmental stages, fbp1 is up-regulated by
pMADS1 in petals. On the other hand, the induction and maintenance of
pMADS1 expression are not affected by fbp1. To obtain information about the
functional interaction between fbp1 and pMADS1, an fbp1 cosuppression
mutant with mild phenotypic alterations was crossed with a green petals
mutant in which pMADS1 expression was abolished. Progeny plants,
heterozygous for the pMADS1 gene, had flowers with a more pronounced
reversion from petals into sepals than was observed for the parent fbp1
mutant. The morphology of the third whorl organs was not changed. These
observations, together with expression levels of pMADS1 and fbp1 in mutant
flowers, provide evidence for functional control of fbp1 by PMADS1 in vivo.
