Complex Patterns of Gene Duplication in the APETALA3 and PISTILLATA Lineages of the Ranunculaceae

It has been proposed that the diversification of the MADS-box gene family of transcription factors has played a major role in the radiation of land plants. This suggestion is based on the critical roles that these genes play in plant development and the apparent coincidence of key duplication events with major radiations, such as the establishment of the B and C lineages concurrent with the evolution of the seed plants. On a more recent scale, it is also possible that subsequent duplication events have contributed to later morphological diversifications. In order to investigate this possibility, we are studying the evolution of homologs of the petal and stamen identity genes APETALA3 (AP3) and PISTILLATA (PI) in the Ranunculaceae. In this family, the AP3 and PI lineages have undergone many duplication events at every phylogenetic level. Early duplications gave rise to three paralogous AP3 lineages, which are found throughout the family. In contrast, numerous duplications have occurred relatively recently in the PI lineage. We outline a hypothesis that these duplications have played a role in the evolution of the unique types of petaloid organs in the Ranunculaceae and present preliminary expression data supporting such a scenario.Organismic and Evolutionary Biolog

Phylogenetic insights into the correlates of dioecy in meadow-rues (Thalictrum, Ranunculaceae)

Numerous studies have examined the evolution of sexual systems in angiosperms, but few explore the interaction between these and the evolution of pollination mode. Wind pollination is often associated with unisexual flowers, but which evolved first and played a causative role in the evolution of the other is unclear. Thalictrum, meadow-rues (Ranunculaceae), provides a unique opportunity to study the evolution of these traits because it contains insect and wind pollination and four sexual systems. We used a phylogenetic approach to reconstruct ancestral states for sexual system, pollination mode, and geographic distribution in Thalictrum, and tested for correlations to uncover the factors involved in the evolution of unisexuality and wind pollination. Our results show that dioecy, andro- and gynomonoecy evolved at least twice from hermaphroditism. Wind pollination, unisexual flowers, and New World distribution were all significantly correlated. Wind pollination may have evolved early in the genus, followed by multiple losses and gains, and likely preceded the origin of unisexual flowers in several cases; we found no evidence for unisexual flowers evolving prior to wind pollination. Given a broad scale study showing the evolution of dioecy before wind pollination, our results from a finer scale analysis highlight that different evolutionary pathways are likely to occur throughout angiosperms.Keywords: ITS, Thalictrum, Dioecy, rpl16, Monoecy, Wind pollinationKeywords: ITS, Thalictrum, Dioecy, rpl16, Monoecy, Wind pollinatio

Geometric morphometrics reveals shifts in flower shape symmetry and size following gene knockdown of CYCLOIDEA and ANTHOCYANIDIN SYNTHASE

Peer reviewe

Patterns of Gene Duplication and Functional Evolution During the Diversification of the AGAMOUS Subfamily of MADS Box Genes in Angiosperms

Members of the AGAMOUS (AG) subfamily of MIKC-type MADS-box genes appear to control the development of reproductive organs in both gymnosperms and angiosperms. To understand the evolution of this subfamily in the flowering plants, we have identified 26 new AG-like genes from 15 diverse angiosperm species. Phylogenetic analyses of these genes within a large data set of AG-like sequences show that ancient gene duplications were critical in shaping the evolution of the subfamily. Before the radiation of extant angiosperms, one event produced the ovule-specific D lineage and the well-characterized C lineage, whose members typically promote stamen and carpel identity as well as floral meristem determinacy. Subsequent duplications in the C lineage resulted in independent instances of paralog subfunctionalization and maintained functional redundancy. Most notably, the functional homologs AG from Arabidopsis and PLENA (PLE) from Antirrhinum are shown to be representatives of separate paralogous lineages rather than simple genetic orthologs. The multiple subfunctionalization events that have occurred in this subfamily highlight the potential for gene duplication to lead to dissociation among genetic modules, thereby allowing an increase in morphological diversity.Organismic and Evolutionary Biolog

A Broader View for Plant EvoDevo: Novel Approaches for Diverse Model Systems

This collection attempts to integrate work pertaining to a fundamental question in plant evolution: What are the molecular underpinnings for the origin of different plant forms? Among the many facets this question touches are the transition to land, the emergence of vascular plants, the origin of the seed and the origin and diversification of floral form. We aim to bring to the forefront the most salient and original plant systems and approaches within an inclusive phylogenetic context that encompasses representatives of the major lineages of land plants

The dynamic pollen tube cytoskeleton: live cell studies using actin-binding and microtubule-binding reporter proteins

Pollen tubes elongate within the pistil to transport sperm cells to the embryo sac for fertilization. Growth occurs exclusively at the tube apex, rendering pollen tube elongation a most dramatic polar cell growth process. A hallmark pollen tube feature is its cytoskeleton, which comprises elaborately organized and dynamic actin microfilaments and microtubules. Pollen tube growth is dependent on the actin cytoskeleton; its organization and regulation have been examined extensively by various approaches, including fluorescent protein labeled actin-binding proteins in live cell studies. Using the previously described GFP-NtADF1 and GFP-LlADF1, and a new actin reporter protein NtPLIM2b-GFP, we re-affirm that the predominant actin structures in elongating tobacco and lily pollen tubes are long, streaming actin cables along the pollen tube shank, and a subapical structure comprising shorter actin cables. The subapical collection of actin microfilaments undergoes dynamic changes, giving rise to the appearance of structures that range from basket- or funnel-shaped, mesh-like to a subtle ring. NtPLIM2b-GFP is used in combination with a guanine nucleotide exchange factor for the Rho GTPases, AtROP-GEF1, to illustrate the use of these actin reporter proteins to explore the linkage between the polar cell growth process and its actin cytoskeleton. Contrary to the actin cytoskeleton, microtubules appear not to play a direct role in supporting the polar cell growth process in angiosperm pollen tubes. Using a microtubule reporter protein based on the microtubule end-binding protein from Arabidopsis AtEB1, GFP-AtEB1, we show that the extensive microtubule network in elongating pollen tubes displays varying degrees of dynamics. These reporter proteins provide versatile tools to explore the functional connection between major structural and signaling components of the polar pollen tube growth process