Abstract
Homologs of the CYC/TB1 gene family have been independently recruited many times across the eudicots to control aspects of floral symmetry The family Asteraceae exhibits the largest known diversification in this gene paralog family accompanied by a parallel morphological floral richness in its specialized head-like inflorescence. In Asteraceae, whether or not CYC/TB1 gene floral symmetry function is preserved along organismic and gene lineages is unknown. In this study, we used phylogenetic, structural and expression analyses focused on the highly derived genus Anacyclus (tribe Anthemidae) to address this question. Phylogenetic reconstruction recovered eight main gene lineages present in Asteraceae: two from CYC1, four from CYC2 and two from CYC3-like genes. The species phylogeny was recovered in most of the gene lineages, allowing the delimitation of orthologous sets of CYC/TB1 genes in Asteraceae. Quantitative real-time PCR analysis indicated that in Anacyclus three of the four isolated CYC2 genes are more highly expressed in ray flowers. The expression of the four AcCYC2 genes overlaps in several organs including the ligule of ray flowers, as well as in anthers and ovules throughout development.
Highlights
Asteraceae is the largest family of vascular plants with more than 23,600 species distributed among 13 different lineages (Panero et al, 2014)
The identified CYCLOIDEA/TEOSINTE BRANCHED1 (CYC/TB1) lineages are unevenly sampled for all the Asteraceae species, each of them is congruent with the species phylogeny (Figure 1)
For tribe Anthemideae, we identified cDNAs from 10 putative CYC/TB1 genes (Figure 1) from A. clavatus (AcCYC1a, AcCYC1b, AcCYC2a, AcCYC2a1, AcCYC2b, AcCYC2c, AcCYC2c1, AcCYC2d, AcCYC3a, and AcCYC3b), three from A. valentinus (AvCYC2b, AcCYC2c1, and AvCYC2d), four from Matricaria aurea (MaCYC2a1, MaCYC2c, MaCYC2c1, and MACYC2d), and three from M. chamomilla (McCYC2b, McCYC2c1, and McCYC2d)
Summary
Asteraceae is the largest family of vascular plants with more than 23,600 species distributed among 13 different lineages (Panero et al, 2014). Variations in perianth morphology, symmetry and sexuality of the flowers along the radial axis of this inflorescence have been used to discriminate different types of capitula (i.e., bilabiate, ligulate, radiate, discoid, and disciform; Jeffrey, 1977; Bremer, 1994). This diversity has important consequences, such as differential attractiveness to pollinators, increased rate of outcrossing and fitness by the presence of peripheral ray flowers (e.g., Senecio; Chapman and Abbott, 2009), or differential rates of seed germination across the capitulum (e.g., Anacyclus; Torices et al, 2013)
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