Evolution of genetic mechanisms controlling petal development

Abstract

Molecular genetic studies in Arabidopsis thaliana and other higher-eudicot flowering plants have led to the development of the 'ABC' model of the determination of organ identity in flowers, in which three classes of gene, A, B and C, are thought to work together to determine organ identity. According to this model, the B-class genes APETALA3 (AP3) and PISTILLATA (PI) act to specify petal and stamen identity. Here we test whether the roles of these genes are conserved throughout the angiosperms by analysing the expression of AP3 and PI orthologues in the lower eudicot subclass Ranunculidae. We show that, although expression of these orthologues in the stamens is conserved, the expression patterns in the petals differ from those found in the higher eudicots. The differences between these expression patterns suggest that the function of AP3 and PI homologues as B-class organ-identity genes is not rigidly conserved among all angiosperms. These observations have important implications for understanding the evolution of both angiosperm petals and the genetic mechanisms that control the identities of floral organs.

The K domain mediates heterodimerization of theArabidopsisfloral organ identity proteins, APETALA3 and PISTILLATA

“…DEF-and GLO-subfamily proteins possess several features in addition to the common features of MIKC-type MADS proteins (Figure 2). First, K1 is more conserved while K3 is less conserved in hydrophobicity at a and d positions in DEF and GLO subfamilies compared to other MADS subfamilies (Kramer, 2000;Theißen et al, 2000). Second, 44 of 46 DEF-subfamily proteins and all GLO-subfamily proteins contain asparagine at position 98, a putative hydrophobic a position in K1.…”

“…More than 70 AP3-and PI-like genes have been cloned from various plant species and have been categorized as members of the DEFICIENS (DEF) and GLOBOSA (GLO) subfamilies (DEF and GLO are the Antirrhinum majus AP3 and PI orthologs) (Kramer et al, 1998;Kramer, 2000;Theißen et al, 1996Theißen et al, , 2000. DEF-and GLO-subfamily proteins possess several features in addition to the common features of MIKC-type MADS proteins (Figure 2).…”

“…Among plant MADS proteins, position 98 is conserved as asparagine only in the DEF and GLO subfamilies (Figure 2) (Kramer, 2000;Theißen et al, 2000). To study the role of Asn-98 in AP3/PI interaction, we mutated Asn-98 to the hydrophobic amino acids leucine and valine (AP3 N98L , AP3 N98V , PI N98V and PI N98L ), and measured protein/protein interactions by yeast two-hybrid assays (Table 1, Figure 3c).…”

Evolution of the Petal and Stamen Developmental Programs: Evidence from Comparative Studies of the Lower Eudicots and Basal Angiosperms

“…of the genes' functions have changed over time (Kramer and Irish 1999). In this article, we will summarize these previous findings and describe the results of more recent analyses of gene sequence and expression patterns in monocot and basal angiosperm species.…”

“…Species classifications are based primarily on the system proposed in APG (1998). Accession numbers are found in Kramer et al (1998) and Kramer and Irish (1999) and in the "Material and Methods" section.…”