Differential expression of two MADS box genes in wild-type and mutant petunia flowers.

Abstract

We isolated and characterired two flower-specific genes from petunia. The protein products of these genes, designated floral binding protein 1 (FBP1) and 2 (FBP2), are putative transcription factors with the MADS box DNA binding domain. RNA gel blot analysis showed that the fbpl gene is exclusively expressed in petals and stamen of petunia flowers. In contrast, the FBP1 protein was only detectable in petals and not in stamens, suggesting posttranscriptional regulation of the fbpl gene in these tissues. The fbp2 gene is expressed in petals, stamen, carpels, and a t a very low leve1 in sepals but not in vegetative tissues. We analyzed the spatial expression of these fbp genes in floral organs of two homeotic flower mutants. In the blind mutant, whose flower limbs are transformed into antheroid structures on top of normal tubes, identical expression levels of both genes were observed in the antheroid structures as in normal anthers. In the homeotic mutant green petals, the petals are replaced by sepaloid organs in which the expression of fbpl is strongly reduced but not completely abolished. Our results suggest a regulation of the fbpl gene expression by the green petals (gp) gene. Expression of the fbp2 gene was not affected in the green petals mutant. In contrast to the proposed models describing floral morphogenesis, our data indicated that homeotic genes can be functional in one whorl only.

Nucleotide sequence of a flower-specific MADS box cDNA clone from orchid

“…The polypeptide (250 amino acids) encoded by oml has a calculated molecular mass of 28 774 Da and exhibits 80.8~o, 78.6~o and 57.3 ~o amino acid identity to FBP2, TM and AgL4 respectively [1,9,6]. A more significant homology could be observed in the N-terminal region when the first 56 amino acid residues of the O-MADS box were aligned to all the other presumptive DNA binding domains listed in Fig.…”

“…The oml transcripts were only detectable in petals and sepals, but not in columns. In petunia flowers, however, the MADS box fbp2 transcripts were barely detected in sepals [ 1 ]. Sepals of orchid flower are morphologically similar to the petals.…”

“…The sole potential calmodulin-dependent phosphorylation site (RQVT) is perfectly conserved in the oml gene whereas the proposed glycosylation site (NKT) is found at amino acid position 164-166. The K box domain (position 109 to 147) is rich in leucine residues and can potentially form an e-helical conformation similar to the leucine zipper motif [1]. It is also interesting to note that, unlike agl-2 and agl-4 which have an unusually long 5'-untranslated region containing a short ORF, the oml gene has only a short untranslated region similar to tm genes [6, 91.…”

“…Although much information has been obtained through horticultural and physiological studies [3,4], little is known about the molecular mechanism underlying its flower formation. Recently, a number of floral homeotic genes have been isolated and characterized in species including Arabidopsis, Antirrhinum, Petunia and tomato [5,6,11,1,9]. Among these development genes, agamous and agamous-like genes have received much attention.…”

“…. An alignment between various MADS box regions: Aranda deborah (orchid), Petunia hybrida (petunia), Lycopersicon esculentum (tomato), Saccharomyces cerevisiae (yeast), Arabidopsis thaliana, Antirrhinum majus (snapdragon), Homo sapiens (man)[ 1,9,8,6,12,11,7]. The number refers to the position in a given ORF of the first residue of the domain.…”