Analysis of thePetunia TM6MADS Box Gene Reveals Functional Divergence within theDEF/AP3Lineage

Abstract

Antirrhinum majus DEFICIENS (DEF) and Arabidopsis thaliana APETALA3 (AP3) MADS box proteins are required to specify petal and stamen identity. Sampling of DEF/AP3 homologs revealed two types of DEF/AP3 proteins, euAP3 and TOMATO MADS BOX GENE6 (TM6), within core eudicots, and we show functional divergence in Petunia hybrida euAP3 and TM6 proteins. Petunia DEF (also known as GREEN PETALS [GP]) is expressed mainly in whorls 2 and 3, and its expression pattern remains unchanged in a blind (bl) mutant background, in which the cadastral C-repression function in the perianth is impaired. Petunia TM6 functions as a B-class organ identity protein only in the determination of stamen identity. Atypically, Petunia TM6 is regulated like a C-class rather than a B-class gene, is expressed mainly in whorls 3 and 4, and is repressed by BL in the perianth, thereby preventing involvement in petal development. A promoter comparison between DEF and TM6 indicates an important change in regulatory elements during or after the duplication that resulted in euAP3-and TM6-type genes. Surprisingly, although TM6 normally is not involved in petal development, 35S-driven TM6 expression can restore petal development in a def (gp) mutant background. Finally, we isolated both euAP3 and TM6 genes from seven solanaceous species, suggesting that a dual euAP3/TM6 B-function system might be the rule in the Solanaceae.

Deciphering the Physalis floridana Double-Layered-Lantern1 Mutant Provides Insights into Functional Divergence of the GLOBOSA Duplicates within the Solanaceae

“…The two duplicates for each lineage redundantly partitioned the role of the B function with a variable subfunctionalization process in Petunia hybrida, Nicotiana benthamiana, and Solanum lycopersicum. This supposition is supported by the observations that a single mutation in each lineage in a species shows a partially mutated B-type phenotype in these Solanaceous species (Vandenbussche et al, 2004;de Martino et al, 2006;Rijpkema et al, 2006;Geuten and Irish, 2010).…”

“…While homodimerization was only detected for the GLO proteins in Physalis floridana, heterodimer pairs GLO1-DEF and GLO2-TM6 were found to form stably in the Solanaceae (Vandenbussche et al, 2004;de Martino et al, 2006;Rijpkema et al, 2006;Geuten and Irish, 2010); however, maximal cross dimerizations were observed in N. benthamiana (Fig. 10).…”

Selection on Length Mutations After Frameshift Can Explain the Origin and Retention of the AP3/DEF-Like Paralogues in Impatiens

“…For these core eudicot plant families, it is reasonable to assume that the euAP3 lineage is represented by one member in the genome. For Solanaceae, we used the data on MADS-box class B genes presented by Rijpkema et al (2006). This dataset contains eight species: Brunfelsia uniflora, Cestrum elegans, Juanulloa aurantiaca, Mandragora autumnalis, Petunia hybrida, Solandra maxima, Solanum lycopersicum, and Solanum pseudolulo.…”

“…Indel substitution events that occurred within the C-terminal domain of this group were mapped onto the Solanaceae tree of Olmstead et al (1999). In this phylogeny, the Cestroideae containing Cestrum elegans are sister to the Solanaceae species that were present in the dataset of Rijpkema et al (2006). Consequently, we separately compared Cestrum elegans with each species from the Solanaceae dataset and counted the number of indel substitutions that had occurred between the outgroup and the examined species.…”

Redefining C and D in the Petunia ABC

“…More recently, it was shown that in Arabidopsis, AG is required for maintenance of AP3 expression during stamen organogenesis, while in developing petals this role is fulfilled by APETALA1 (AP1) (Gómez-Mena et al, 2005). We were particularly interested to further investigate this aspect of C-dependent B-gene expression maintenance in petunia to better understand the evolutionary divergence between the two B-class genes DEFICIENS (DEF), the petunia AP3 ortholog (van der Vandenbussche et al, 2004), and TM6 (Rijpkema et al, 2006), a member of a more ancient B-class lineage gene that has been lost in Arabidopsis but is present in most of the eudicot species investigated so far (Kramer et al, 1998). TM6 is a paleoAP3 gene expressed, atypically for a B-function gene, in the third and fourth whorls.…”