Control of petal shape and floral zygomorphy in Lotus japonicus

Abstract

Zygomorphic flowers, with bilateral (dorsoventral) symmetry, are considered to have evolved several times independently in flowering plants. In Antirrhinum majus, floral dorsoventral symmetry depends on the activity of two TCP-box genes, CYCLOIDEA (CYC) and DICHOTOMA (DICH). To examine whether the same molecular mechanism of floral asymmetry operates in the distantly related Rosid clade of eudicots, in which asymmetric flowers are thought to have evolved independently, we investigated the function of a CYC homologue LjCYC2 in a papilionoid legume, Lotus japonicus. We showed a role for LjCYC2 in establishing dorsal identity by altering its expression in transgenic plants and analyzing its mutant allele squared standard 1 (squ1). Furthermore, we identified a lateralizing factor, Keeled wings in Lotus 1 (Kew1), which plays a key role in the control of lateral petal identity, and found LjCYC2 interacted with Kew1, resulting in a double mutant that bore all petals with ventralized identity to some extents. Thus, we demonstrate that CYC homologues have been independently recruited as determinants of petal identities along the dorsoventral axis in two distant lineages of flowering plants, suggesting a common molecular origin for the mechanisms controlling floral zygomorphy.dorsoventral axis ͉ floral development ͉ keeled wings in Lotus ͉ LjCYC2 ͉ squared standard

Wrinkled petals and stamens 1, is required for the morphogenesis of petals and stamens in Lotus japonicus

“…As a normal papilionoid legume, there are three types of petals in wild type flower of L. japonicus: standard, wing and keel, arranging along a dorsoventral axis of the flower [21], which display different shapes ( Figure 1B). Representative cells can be recognized at the epidermal layer among different petals: the conical cells in the standard ( Figure 4A); the jigsaw puzzle-shaped cells in Figure 4C).…”

“…Recent study showed that these representative cell types could be used as morphological markers to distinguish the dorsoventral identity of different petal types (Our unpublished data). We examined if there was any alteration in the dorsoventral identity among different types of petals by comparing the morphology of the adaxial epidermal cells in mature petals [21] between the wild type and wps1 mutant. It was found that the characteristic shapes of representative epidermal cells could be clearly identified in the petals of wps1, similar to the ones in wild type (Figure 4 A-4F).…”

“…TM0123 TM0050 TM0193 TM0117 TM0001 TM0122 TM0134 TM0065 TM0225 TM0124 TM0020 TM0002 TM0436 TM0190 TM0155 TM0142 TM0049 TM0203 TM0127 TM0288 TM0182 TM0247 TM0030 TM0046 TM0218 TM0095 TM0048 TM0062 TM0072 TM0146 TM0014 TM0057 TM0140 TM0066 TM0336 TM0314 * [17][18][19]. Our previous work has demonstrated that L. japonicus is an excellent system to dissect the components in the pathway to control floral development [20,21]. A large scale of ethyl methanesulfonate (EMS) mutagenesis experiment has been conducted to screen mutations which affect floral development at various stages in L. japonicus.…”

Evolution of flower shape in Plantago lanceolata

“…CYC-like genes are expressed in a generalized dorsoventral pre-pattern in meristems involved in both flower and shoot formation, even in species with actinomorphic flowers, suggesting that the origin of the genes predates their role in zygomorphy (Cubas et al 2001;Clark and Coen 2002). However, it is only in zygomorphic species that CYC-like gene expression is maintained during flower development in dorsal floral organs (Luo et al 1996;Luo et al 1999;Cubas et al 1999b;Feng et al 2006;Citerne et al 2006;Wang et al 2008). This acquisition and maintenance of CYC expression in dorsal floral organs may have been the driving force behind the evolution of dorsoventral floral asymmetry (Clark and Coen 2002).…”

“…In Mohavea, an expansion of the domain of expression of CYC-like genes during flower development correlates with this derived floral morphology . CYC-like genes have also played a role in the evolution of flower shape in legumes (Feng et al 2006;Citerne et al 2006;Wang et al 2008). In the zygomorphic papilinonoid legume Lupinus nanus, a CYC-like gene is expressed in dorsal floral regions in a pattern similar to Antirrhinum (Citerne et al 2006).…”