The MIK region rather than the C‐terminal domain of AP3‐like class B floral homeotic proteins determines functional specificity in the development and evolution of petals

Abstract

Summary• In core eudicots, euAP3-type MADS-box genes encode a PISTILLATA (PI)-derived motif, as well as a C-terminal euAP3 motif that originated from a paleoAP3 motif of an ancestral APETALA3 (AP3)-like protein through a translational frameshift mutation. To determine the functional and evolutionary relevance of these motifs, a series of point mutation and domain-swap constructs were generated, involving CsAP3, a paleoAP3-type gene from the basal angiosperm Chloranthus spicatus encoding a truncated paleo-AP3 motif, and AtAP3, a euAP3-type gene from the core eudicot Arabidopsis thaliana.• The chimeric constructs were expressed in A. thaliana under the control of the AP3 promoter or the CaMV 35S promoter in an ap3 mutant or wild-type background, respectively.• Significant recovery of AP3 function was obtained in both complementation and ectopic expression experiments whenever the region upstream of the C-terminal motifs (MIK region) from A. thaliana was taken, even when the PI-derived motif and the truncated paleoAP3 motif of CsAP3 substituted for the corresponding sequences from AtAP3. However, no or very weak complementation or gain-of-function was seen when the MIK region was from CsAP3.• Our data suggest that changes in the MIK region rather than mutations in the C-terminal domain were of crucial importance for the evolution of the functional specificity of euAP3-type proteins in stamen and petal development.

B-Function Expression in the Flower Center Underlies the Homeotic Phenotype ofLacandonia schismatica(Triuridaceae)

“…The 35S:LsAP3 construct was insufficient to complement a loss of petal identity in ap3-3 plants ( Figure 4M) (Xu et al, 2006;Su et al, 2008). However, the relatively well-conserved MIK domains of Ls-AP3 correlate with the capacity of this protein to specify stamen identity in Arabidopsis.…”

TheseirenaB Class Floral Homeotic Mutant of California Poppy (Eschscholzia californica) Reveals a Function of the Enigmatic PI Motif in the Formation of Specific Multimeric MADS Domain Protein Complexes

“…Furthermore, mutant and RNA interference analyses of another legume PI protein, Mt-PI from M. truncatula, which is similar in structure to Ps-PI, also supports the view that the C-terminal domain is not required for B class protein activity (Tzeng et al, 2004;Benlloch et al, 2009). Therefore, one wonders why the motifs within the C-terminal domain of class B proteins have been conserved for over 100 million years of evolution (Su et al, 2008).…”

Ectopic expression of an AP3-like and a PI-like genes from 'Sekkoku' orchid (Dendrobium moniliforme) causes the homeotic conversion of sepals to petals in whorl 1 and the suppression of carpel development in whorl 4 in Arabidopsis flowers

“…These results suggest that DMAP3B, a paleotype AP3 gene, might not function in accordance with euAP3 in Arabidopsis to generate the phenotype seen in the overexpresser, because the differentiation between sequences of DMAP3B and AP3 especially in the conserved Cterminal sequence of euAP3, the sequence is distinct and thought to have a different function from paleoAP3 (Lamb and Irish 2003;Vandenbussche et al 2004). However, the MIK region rather than the C-terminal domain of AP3-like class B floral homeotic proteins has been suggested to play action dominated in the development of floral organs particularly in promotion of petal identity (Su et al 2008). Therefore another possible reason is that DMAP3B may play only a minor role in the control of stamen development in orchids; thus, its expression level might not be sufficient to promote the conversion of carpels to stamens in Arabidopsis.…”

“…As the expression patterns of the DEF-like genes in monocot and basal angiosperm are various, the functions of these genes may not be strictly conserved throughout angiosperm (Hsu and Yang 2002;Kim et al 2005;Kramer and Irish 2000;Su et al 2008;Whipple et al 2007). For example, a paleoAP3-line gene (Silky1) in maize can complement Arabidopsis ap3 mutant, suggesting that Siky1 has a conserved function to Arabidopsis AP3 gene in regulating of petal and stamen identity (Su et al 2008;Whipple et al 2004).…”

“…For example, a paleoAP3-line gene (Silky1) in maize can complement Arabidopsis ap3 mutant, suggesting that Siky1 has a conserved function to Arabidopsis AP3 gene in regulating of petal and stamen identity (Su et al 2008;Whipple et al 2004).…”