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Differential transcriptome analysis reveals insight into monosymmetric corolla development of the crucifer Iberis amara

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Background In the co-evolution between insects and plants, the establishment of floral monosymmetry was an important step in angiosperm development as it facilitated the interaction with insect pollinators and, by that, likely enhanced angiosperm diversification. In Antirrhiunm majus, the TCP transcription factor CYCLOIDEA is the molecular key regulator driving the formation of floral monosymmetry. Although most Brassicaceae form a polysymmetric corolla, six genera develop monosymmetric flowers with two petal pairs of unequal size. In the monosymmetric crucifer Iberis amara, formation of the different petal pairs coincides with a stronger expression of the CYC-homolog IaTCP1 in the small, adaxial petals.ResultsIn this study, RNA-Seq was employed to reconstruct the petal transcriptome of the non-model species Iberis amara. About 9 Gb of sequence data was generated, processed and re-assembled into 18,139 likely Iberis unigenes, from which 15,983 showed high sequence homology to Arabidopsis proteins. The transcriptome gives detailed insight into the molecular mechanisms governing late petal development. In addition, it was used as a scaffold to detect genes differentially expressed between the small, adaxial and the large, abaxial petals in order to understand the molecular mechanisms driving unequal petal growth. Far more genes are expressed in adaxial compared to abaxial petals implying that IaTCP1 activates more genes than it represses. Amongst all genes upregulated in adaxial petals, a significantly enhanced proportion is associated with cell wall modification and cell-cell signalling processes. Furthermore, microarrays were used to detect and compare quantitative differences in TCP target genes in transgenic Arabidopsis plants ectopically expressing different TCP transcription factors.Conclusions The increased occurrences of genes implicated in cell wall modification and signalling implies that unequal petal growth is achieved through an earlier stop of the cell proliferation phase in the small, adaxial petals, followed by the onset of cell expansion. This process, which forms the monosymmetric corolla of Iberis amara, is likely driven by the enhanced activity of IaTCP1 in adaxial petals.
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... genome of T. hassleriana [7], as well as on transcriptomic libraries from this and other species [35,36]. For example, TCP1 plays a crucial role in the transition from polysymmetric (multiple planes of symmetry) to monosymmetric (single plane of symmetry) flowers [37,38], and multiple copies are often associated with evolution of monosymmetry (reviewed in [38]). Disymmetry (two planes of symmetry)-dominated Brassicaceae retain one copy of TCP1 [39], whereas there are at least two copies of TCP1 in at least some Cleomaceae, which has predominantly monosymmetric flowers [7]. ...
... For instance, Tarenaya hassleriana and Arivela viscosa have equally sized petals, whereas Cleome violacea and C. africana have unequally sized petals (Figure 1). Differences in flower petal size in Iberis amara (Brassicaceae) are driven by increased TCP1 expression [37,39], which raises the question of whether the same or alternative mechanisms drive petalsize differences in Cleomaceae. Perhaps more directly related to pollination attraction, petal color ranges from pink to purple, or yellow to white or dull greenish, or orange to red [1] ( Table 1). ...
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Cleomaceae is a diverse group well-suited to addressing fundamental genomic and evolutionary questions as the sister group to Brassicaceae, facilitating transfer of knowledge from the model Arabidopsis thaliana. Phylogenetic and taxonomic revisions provide a framework for examining the evolution of substantive morphological and physiology diversity in Cleomaceae, but not necessarily in Brassicaceae. The investigation of both nested and contrasting whole-genome duplications (WGDs) between Cleomaceae and Brassicaceae allows comparisons of independently duplicated genes and investigation of whether they may be drivers of the observed innovations. Further, a wealth of outstanding genetic research has provided insight into how the important alternative carbon fixation pathway, C4 photosynthesis, has evolved via differential expression of a suite of genes, of which the underlying mechanisms are being elucidated.
... Overall, GO terms within fruits and between species are similar (Fig 3 and S1 Fig), as expected, because all sections and replicates are from developing fruit with shared components (e.g., ovary wall, septum). Additionally, GO analyses of top terms do not usually vary between closely related species [64,65]. However, despite similarities in gene ontology, the origin of heteroarthrocarpy may still be explained by deviation in expression patterns of one or more of the valve margin pathway genes [18,[22][23][24][25][26]. ...
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