The petunia AGL6 gene has a SEPALLATA‐like function in floral patterning

Abstract

SUMMARYSEPALLATA (SEP) MADS-box genes are required for the regulation of floral meristem determinacy and the specification of sepals, petals, stamens, carpels and ovules, specifically in angiosperms. The SEP subfamily is closely related to the AGAMOUS LIKE6 (AGL6) and SQUAMOSA (SQUA) subfamilies. So far, of these three groups only AGL6-like genes have been found in extant gymnosperms. AGL6 genes are more similar to SEP than to SQUA genes, both in sequence and in expression pattern. Despite the ancestry and wide distribution of AGL6-like MADS-box genes, not a single loss-of-function mutant exhibiting a clear phenotype has yet been reported; consequently the function of AGL6-like genes has remained elusive. Here, we characterize the Petunia hybrida AGL6 (PhAGL6, formerly called PETUNIA MADS BOX GENE4/pMADS4) gene, and show that it functions redundantly with the SEP genes FLORAL BINDING PROTEIN2 (FBP2) and FBP5 in petal and anther development. Moreover, expression analysis suggests a function for PhAGL6 in ovary and ovule development. The PhAGL6 and FBP2 proteins interact in in vitro experiments overall with the same partners, indicating that the two proteins are biochemically quite similar. It will be interesting to determine the functions of AGL6-like genes of other species, especially those of gymnosperms.

MADS-domain transcription factors and the floral quartet model of flower development: linking plant development and evolution

“…2, perspective 1; Zahn et al, 2005;Baum and Hileman, 2006;Silva et al, 2016). However, recent experimental data from different species suggest that not only SEPlike but also AGL6-like genes can exert the E function (Thompson et al, 2009;Rijpkema et al, 2009;Hsu et al, 2014) and phylogeny reconstructions suggest that the genomes of extant conifers and the MRCA of extant seed plants contain(ed) orthologs of floral homeotic class A and E genes (Gramzow et al, 2014). It is conceivable, therefore, that FQCs quite similar to those of extant floral quartets also exist in extant gymnosperms and were already established in the MRCA of extant seed plants (Fig.…”

“…According to Causier et al, (A) function is provided by a group of genes, but if one focusses on the MADS-box genes involved -in the case of A. thaliana the class A gene AP1 and the class E genes (sensu lato), i.e. the SEP genes and the AGL6-like genes (Mandel et al, 1992;Pelaz et al, 2000;Ditta et al, 2004;Rijpkema et al, 2009;Hsu et al, 2014) -one finds some support for the new (A) function in gene phylogeny. All of these genes are relatively closely related members of a gene superclade Ruelens et al, 2013), and it is thus conceivable that the A and E functions known from flowering plants trace back to an ancestral function in specifying reproductive meristem identity (Box 2).…”

Developmental and evolutionary diversity of plant MADS-domain factors: insights from recent studies

“…Recent analysis of the function of SQUA subfamily genes from basal eudicots suggests that the 'Afunction' evolved via subfunctionalization after gene duplication(s) at the base of core eudicots from a more broad action of SQUA subfamily members in floral meristem specification, floral organ specification and fruit development [see Pabón-Mora et al (Pabón-Mora et al, 2012) and references therein]. Interestingly, the E function appears to be exerted not only by genes from the SEP subfamily, but also by the closely related AGL6 subfamily, at least in some flowering plant species such as petunia (Vandenbussche et al, 2003b;Rijpkema et al, 2009), rice (Ohmori et al, 2009;Cui et al, 2010;Gao et al, 2010;Li et al, 2011) and maize (Thompson et al, 2009). This provides an indication that partial functional redundancy of members from different subfamilies might have persisted over long evolutionary time-scales.…”

The AGL6-like gene OsMADS6 regulates floral organ and meristem identities in rice

“…Overexpression of AGL6 orthologs from orchid (Oncidium Gower Ramsey) [51] and from hyacinth (Hyacinthus orientalis) [52] has been shown to promote flowering and cause flower homeotic transformation in Arabidopsis. Rijpkema et al [53] have recently revealed that the Petunia hybrida AGL6 (PhAGL6, formerly called PETUNIA MADS-BOX GENE4/pMADS4) gene functions redundantly with the SEP genes, FLORAL BINDING PROTEIN2 (FBP2) and FBP5, in specifying petal and anther development. Reinheimer and Kellogg [50] have analyzed the molecular evolution and expression pattern of the grass AGL6-like genes.…”