Conservation and canalization of gene expression during angiosperm diversification accompany the origin and evolution of the flower

Abstract

The origin and rapid diversification of the angiosperms (Darwin's "Abominable Mystery") has engaged generations of researchers. Here, we examine the floral genetic programs of phylogenetically pivotal angiosperms (water lily, avocado, California poppy, and Arabidopsis) and a nonflowering seed plant (a cycad) to obtain insight into the origin and subsequent evolution of the flower. Transcriptional cascades with broadly overlapping spatial domains, resembling the hypothesized ancestral gymnosperm program, are deployed across morphologically intergrading organs in water lily and avocado flowers. In contrast, spatially discrete transcriptional programs in distinct floral organs characterize the more recently derived angiosperm lineages represented by California poppy and Arabidopsis. Deep evolutionary conservation in the genetic programs of putatively homologous floral organs traces to those operating in gymnosperm reproductive cones. Female gymnosperm cones and angiosperm carpels share conserved genetic features, which may be associated with the ovule developmental program common to both organs. However, male gymnosperm cones share genetic features with both perianth (sterile attractive and protective) organs and stamens, supporting the evolutionary origin of the floral perianth from the male genetic program of seed plants.

Comparative Transcriptional Profiling Provides Insights into the Evolution and Development of the Zygomorphic Flower of Vicia sativa (Papilionoideae)

“…Using log2 floral organ/non-adjacent-organ gene expression values (Ratio>2.0 and Z-score>3.75), we obtained a total of 3,903 Arabidopsis transcripts and 20,714 vetch unigenes enriched in the floral organs. Similar to the results for Arabidopsis [40], the enriched vetch transcripts demonstrated sharp boundaries among the different floral organs (Figure 2A). Based on all of the transcript expression data for Arabidopsis (21,972 genes) and vetch (71,553 unigenes), we constructed scatter plots for the adjacent floral organ categories.…”

“…We further compared the spatial distribution of floral-biased expression in vetch and Arabidopsis flowers [40]. Using log2 floral organ/non-adjacent-organ gene expression values (Ratio>2.0 and Z-score>3.75), we obtained a total of 3,903 Arabidopsis transcripts and 20,714 vetch unigenes enriched in the floral organs.…”

Generation of a large-scale genomic resource for functional and comparative genomics in Liriodendron tulipifera L.

“…This can lead to biasing evolutionary comparisons. Since the first L. tulipifera EST dataset became available, Liriodendron has been used a comparator to better understand the evolution of the origin and evolution of the flower (Zahn et al 2005Soltis et al 2007;Chanderbali et al 2010), as well as ancestral polyploidy in seed plants and angiosperms (CW dePamphilis, personal communication). Built from ten different tissue types, the new EST dataset is by far the most comprehensive genomic resource for Liriodendron.…”

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').…”