The Petunia MADS Box Gene FBP11 Determines Ovule Identity

Abstract

In contrast to the wealth of information relating to genes regulating floral meristem and floral organ identity, only limited data are available concerning genes that are involved in determining and regulating the identity and development of an ovule. We have recently isolated the floral binding protein 11 (FBP11) MADS box gene from petunia and found that it is expressed exclusively in ovule primordia and subsequently in the ovules, suggesting a role for this gene in ovule formation. To test this hypothesis, we constructed a recombinant gene in which the full-size FBP11 cDNA was placed under the control of a strong cauliflower mosaic virus 35S promoter. Transgenic petunia plants expressing this chimeric gene have ovulelike structures on the adaxial side of the sepals and the abaxial side of the petals. Detailed morphological studies showed that these ovulelike structures are true ovules. RNA gel blot analysis was performed to investigate ectopic FBP11 expression in relation to the expression of the closely related FBP7 gene and the putative petunia class C-type homeotic genes FBP6 and pMADS3. Our results indicate that FBP11 represents an ovule identity gene. A new model describing the mode of action of FBP11 as an additional class D MADS box gene is presented.

Regulation of Ovule Development

“…This expression pattern is similar to that of STK, SHP1, and SHP2. FBP11 and FBP7 have been reported to cause occasional formation of ovules on sepals, petals, and carpels when expressed ectopically (Colombo et al, 1995;Cheng et al, 2000). However, both the sepals and petals in these plants showed other phenotypes correlated with the acquisition of carpel identity.…”

MADS-Box Protein Complexes Control Carpel and Ovule Development in Arabidopsis

“…This finding led to the conclusion that, at least in petunia, these two MADS-box genes were sufficient to induce ovule development without the presence of carpel structures. Although this might be true, molecular analysis showed that in the sepals and petals of these transgenic petunia plants, the class-C genes FBP6 and pMADS3 are induced (Colombo et al, 1995). That the induction of these genes did not result in severe homeotic conversions of sepals to carpeloid organs is not surprising, because the overexpression of FBP6 does not have any effect on sepals, and ectopic pMADS3 expression had only a very mild effect on sepals (Tsuchimoto et al, 1993;Kater et al, 1998).…”

“…Previous experiments showed that the redundant petunia genes FBP7 and FBP11 were necessary for ovule identity determination and sufficient to induce ectopic ovule formation on sepals and petals (Colombo et al, 1995). STK is highly similar to these petunia genes and, together with SHP1 and SHP2 , essential for ovule formation (Pinyopich et al, 2003).…”

“…Until recently, the Arabidopsis genes that control ovule identity determination were not identified. The only information on this early phase in ovule development came from studies in petunia, in which two redundant MADS-box genes, FBP7 and FBP11, which specify ovule identity, were identified Colombo et al, 1995). Cosuppression of both genes resulted in the homeotic conversion of ovules to carpeloid structures, and ectopic expression of these genes induced ectopic ovule formation on sepals and petals.…”

Identification and Characterization of Four Chrysanthemum MADS-Box Genes, Belonging to the APETALA1/FRUITFULL and SEPALLATA3 Subfamilies

“…Additional functions were identified, mainly by studies with petunia (Petunia hybrida). Two redundant MADS-box proteins, floral binding proteins (FBP) 7 and 11 appeared to determine the identity of ovules, which arise from the remaining floral meristem after the carpel primordia are formed (Angenent et al, 1995;Colombo et al, 1995). Since then these ovule identity genes represent the D-function.…”