View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by MURAL - Maynooth University Research Archive Library Plant Mol Biol (2009) 71:241–250 DOI 10.1007/s11103-009-9520-z Evolution of flower shape in Plantago lanceolata Wesley Reardon Æ David A. Fitzpatrick Æ Mario A. Fares Æ Jacqueline M. Nugent Received: 16 December 2008 / Accepted: 25 June 2009 / Published online: 11 July 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Plantago lanceolata produces small actino- Introduction morphic (radially symmetric), wind-pollinated flowers that have evolved from a zygomorphic, biotically pollinated Flowering plants have evolved huge diversity in their floral ancestral state. To understand the developmental mecha- form and in their pollination strategies. One of the most nisms that might underlie this change in flower shape, and variable morphological characters is flower shape. Flowers associated change in pollination syndrome, we analyzed can be classified as zygomorphic (having only one plane of the role of CYC-like genes in P. lanceolata. Related reflectional symmetry or bilaterally symmetric), actino- zygomorphic species have two CYC-like genes that are morphic (having multiple planes of symmetry or radially expressed asymmetrically in the dorsal region of young symmetric) or asymmetric (having no plane of symmetry) floral meristems and in developing flowers, where they (Endress 2001). The gene regulatory network that deter- affect the rate of development of dorsal petals and stamens. mines zygomorphy is best understood in the model plant Plantago has a single CYC-like gene (PlCYC) that is not Antirrhinum majus (Corley et al. 2005). In Antirrhinum expressed in early floral meristems and there is no apparent zygomorphy is evident primarily in the distinct shape of the asymmetry in the pattern of PlCYC expression during later dorsal, lateral and ventral petals of the flower (Fig. 1a, flower development. Thus, the evolution of actinomorphy Corley et al. 2005). Two genes, CYCLOIDEA (CYC) and in Plantago correlates with loss of dorsal-specific CYC-like DICHOTOMA (DICH), play a key role in promoting dorsal gene function. PlCYC is expressed in the inflorescence identity in Antirrhinum (Luo et al. 1996, 1999). CYC and stem, in pedicels, and relatively late in stamen develop- DICH are paralogous genes (CYC-like genes); both are ment, suggesting a novel role for PlCYC in compacting the expressed throughout floral development in dorsal regions inflorescence and retarding stamen elongation in this wind and encode proteins belonging to the TCP family of tran- pollinated species. scription factors (Cubas et al. 1999a). In addition to affecting petal shape, CYC-like gene activity in dorsal Keywords Plantago Á Flower shape Á Protogyny Á regions inhibits stamen growth in Antirrhinum and the Wind pollination Á CYCLOIDEA dorsal stamen is reduced to a staminode (Luo et al. 1996; Luo et al. 1999). In Antirrhinum cyc/dich double mutant plants produce flowers that are actinomorphic, with all petals and stamens resembling the ventral petals and sta- mens of wild-type flowers (Carpenter and Coen 1990). Zygomorphic flowers have evolved independently from W. Reardon Á D. A. Fitzpatrick Á J. M. Nugent (&) Department of Biology, National University of Ireland, actinomorphic ancestors many times throughout flowering Maynooth, Co. Kildare, Ireland plant evolution (Stebbins 1974; Donoghue et al. 1998; e-mail: [email protected] Endress 2001). CYC-like genes have been co-opted into at least two separate genetic programs promoting floral M. A. Fares Department of Genetics, Smurfit Institute of Genetics, Trinity asymmetry in angiosperms, once within the asterids College, Dublin, Ireland (Antirrhinum and relatives), and once within the rosids 123 242 Plant Mol Biol (2009) 71:241–250 (a) (b) Antirrhinum (Z) (biotic pollination) ZA Digitalis (NZ) Veronica (NZ) Plantago (A) (wind pollination) Fig. 1 P. lanceolata flowers are actinomorphic and wind pollinated inferred to have had zygomorphic flowers (ZA = zygomorphic and are derived from a zygomorphic and biotic pollinated ancestral ancestor; NZ = near zygomorphy); b P. lanceolata produces a state. a Schematic representation of the progression from zygomorphy compact inflorescence of small, actinomorphic, wind-pollinated (Z), and biotic pollination, to actinomorphy (A), and wind pollination, flowers subtended by a leafless scape. Stamen exsertion and floral within the Veronicaceae (only some representative genera are shown anthesis proceeds from the bottom to the top of the inflorescence after and flowers are not drawn to scale). The ancestor of this clade is female flowering (image courtesy of Steven J. Baskauf) (Lotus and other legumes) (Cubas 2004). CYC-like genes However, in the closely related but actinomorphic, species are expressed in a generalized dorsoventral pre-pattern in Cadia purpurea, CYC-like gene expression occurs in all meristems involved in both flower and shoot formation, floral regions (Citerne et al. 2006). Thus, in Cadia and even in species with actinomorphic flowers, suggesting that Mohavea, loss of zygomorphy is not achieved by a loss of the origin of the genes predates their role in zygomorphy function event, but by a regulatory event that results in an (Cubas et al. 2001; Clark and Coen 2002). However, it is expansion of the domain of CYC-like gene expression only in zygomorphic species that CYC-like gene expression during flower development. CYC-like genes also affect the is maintained during flower development in dorsal floral rate of stamen development and eventual stamen size in organs (Luo et al. 1996; Luo et al. 1999; Cubas et al. legumes (Citerne et al. 2006). 1999b; Hileman et al. 2003; Feng et al. 2006; Citerne et al. Zygomorphic flowers predominate within the Lamiales, 2006; Wang et al. 2008). This acquisition and maintenance although the basal lineages produce actinomorphic flowers of CYC expression in dorsal floral organs may have been (Endress 1997; Olmstead et al. 2000; Bremer et al. 2002). the driving force behind the evolution of dorsoventral floral Molecular systematic studies of species within the Lamiales asymmetry (Clark and Coen 2002). Changes in the regu- place Antirrhinum within the Veronicaceae, a very highly lation of CYC-like genes have also played a causal role in supported clade that includes the Antirrhineae, Digitaleae the evolution of derived zygomorphic variants within the and Plantaginaceae (Olmstead et al. 2001). Within this clade Antirrhineae. Mohavea confertiflora has zygomorphic there is a progression from pronounced zygomorphy in flowers with three stamens aborted (one dorsal and two Antirrhinum to reduced zygomorphy in Digitalis and lateral), and a corolla that is more radially symmetrical Veronica, to actinomorphy in Plantago, accompanied by a than the corolla of the Antirrhinum flower. In Mohavea, an shift from biotic to wind pollination (Fig. 1a). Wind polli- expansion of the domain of expression of CYC-like genes nation (anemophily) is predominantly a derived condition in during flower development correlates with this derived flowering plants, and has evolved at least 65 times from floral morphology (Hileman et al. 2003). CYC-like genes biotically pollinated ancestors (Friedman and Barrett 2008). have also played a role in the evolution of flower shape in Wind pollinated plants tend to share several morphological legumes (Feng et al. 2006; Citerne et al. 2006; Wang et al. traits that constitute the ‘‘anemophilous syndrome’’ includ- 2008). In the zygomorphic papilinonoid legume Lupinus ing small unisexual or dichogamous flowers (have temporal nanus, a CYC-like gene is expressed in dorsal floral regions separation of male and female organs within a flower) and in a pattern similar to Antirrhinum (Citerne et al. 2006). condensed inflorescences borne on elongate subtending 123 Plant Mol Biol (2009) 71:241–250 243 internodes (Culley et al. 2002; Weller et al. 2006; Friedman sequences is \1.1%. This is within the range of sequence and Barrett 2008). Two forms of dichogamy exist: protandry divergence rates reported for other CYC-like alleles in the (male phase precedes female) and protogyny (female phase Veronicaceae (0.53–1.42%, Hileman and Baum 2003) precedes male). Protandry is generally associated with biotic suggesting that all Plantago sequences represent alleles of pollination and protogyny is generally associated with wind a single CYC-like gene locus (PlCYC). Phylogenetic pollination (Bertin and Newman 1993). Phylogenetic anal- analyses were carried out with one of the Plantago ysis points to a possible link between floral symmetry and sequences and CYC-like gene sequences from other dichogamy: within the Asteridae protandry has been lost Veronicaceae to assess gene orthology. Maximum likeli- more frequently than expected in actinomorphic clades and hood and Bayesian methods yielded a single tree (Fig. 2). has been gained more frequently than expected in zygo- The Plantago sequence emerges as sister group to the morphic clades. This suggests that zygomorphy and prot- Digitalis CYC2 and CYC3 genes that have arisen as a result andry may be correlated and potentially controlled by the of a recent gene duplication event within the Digitalis same regulatory genes (Kalisz et al. 2006). lineage (Hileman and Baum 2003). Both the ML and The phylogenetic placement of Plantago within the Baysian trees suggest a CYC-like gene duplication event Veronicaceae makes it an excellent system in which to occurred before the radiation of the Antirrhineae, giving investigate