A Developmental Genetic Model for the Origin of the Flower

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

“…Jack, 2001;Eckardt, 2003;Ferrario et al, 2004;Jack, 2004;Krizek and Fletcher, 2005;Baum and Hileman, 2006), suggesting that it was plausible and not in conflict with major evidence at the time of its inception. In addition, a number of protein interaction studies in yeast using proteins from different flowering plant species, such as Class A genes are expressed in the organ primordia of the 1st and the 2nd whorl of the flower, class B genes in the 2nd and 3rd whorl, class C genes in whorls 3 and 4, class D genes in parts of the 4th whorl (ovule primordia), and class E genes are expressed throughout all four whorls.…”

“…These findings led to the view that the origin of SEP-like genes and the incorporation of SEP-like proteins into FQCs have been important steps during the origin of floral quartets, and hence floral organ identity and flower development (Fig. 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).…”

The poetry of reproduction: the role of LEAFY in Arabidopsis thaliana flower formation

“…Thus, the presence or absence of LFY or NLY does not explain the development of bisexual flowers, although it does not disprove the "mostly male" theory. Other theories for the origin of the flower have postulated that spatial changes in B class MADS box genes (Theissen et al, 2000;Theissen and Becker, 2004) or concerted changes of LFY, LFY co-factors and MADS box genes (Baum and Hileman, 2006) could underlie the transition to hermaphroditic flowers. The absence of LFY-like gene expression in apical meristems that are undergoing more sustained indeterminate growth in gymnosperms such as Picea and its presence in those meristem that form reduced numbers of ovule-bearing scales such as Podocarpus does suggest that LFY-like genes confer determinate growth, similar to its function in angiosperm flowers (Vazquez-Lobo et al, 2007).…”

Evolution of floral diversity: genomics, genes andgamma

“…Among these are novel ideas about how flowers evolved from transformed gymnosperm cones [13][14][15][16], an ancestral 'fading borders' model for flower development [17][18][19][20] and floral diversification through 'sliding boundaries' of organ identity functions [21][22][23][24]. The prototypical flower is composed of four types of organs arranged such that carpels (the female reproductive organs, collectively the 'gynoecium') are innermost and surrounded by stamens (the male reproductive organs, collectively 'androecium') which are, in turn, surrounded by petals (usually colourful, collectively 'corolla') and then sepals (leaf-like, collectively 'calyx').…”

“…Variations in the number and arrangement of these four primary floral organs account for much of floral diversity, and can now be understood in the context of genetic specification of floral organ identity [25][26][27] and floral symmetry [28]. Floral evo-devo studies also offer explanations for the origins of stamens and carpels from gymnosperm precursors via 'mostly male', 'out-of-male' and 'out-of-female' mechanisms [14][15][16], and the origins of petals from stamens (andropetals) or bracts (bracteopetals) during the course of angiosperm diversification [29,30].…”