FUNCTIONAL INTERACTION BETWEEN THE HOMEOTIC GENES FBP1 AND PMADS1 DURING PETUNIA FLORAL ORGANOGENESIS

The petunia MADS box floral binding protein (fbp) gene 1 represents a class B homeotic gene determining the identity of second and third flo ral whorl organs. Suppression of fbp1, which is highly homologous to t he Antirrhinum gene globosa and Arabidopsis gene pistillata, results i n the conversion of petals to sepals and stamens to carpels, In contra st to fbp1, the petunia homeotic gene pMADS1, encoding a protein homol ogous to the Antirrhinum protein DEFICIENS, has been shown to be invol ved in the formation of petals only, We demonstrated that the inductio n of fbp1 is established independent of pMADS1, whereas at later devel opmental stages, fbp1 is up-regulated by pMADS1 in petals. On the othe r hand, the induction and maintenance of pMADS1 expression are not aff ected by fbp1, To obtain information about the functional interaction between fbp1 and pMADS1, an fbp1 cosuppression mutant with mild phenot ypic alterations was crossed with a green petals mutant in which pMADS 1 expression was abolished. Progeny plants, heterozygous for the pMADS 1 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 e vidence for functional control of fbp1 by PMADS1 in vivo.