Hélène L Citerne

Publications (4)21.77 Total impact

• Source

  Available from: Quentin Cronk

  Article: An apparent reversal in floral symmetry in the legume Cadia is a homeotic transformation.

  Hélène L Citerne, R Toby Pennington, Quentin C B Cronk
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  ABSTRACT: Within papilionoid legumes, characterized by flowers with strong bilateral symmetry, a derived condition within angiosperms, Cadia (Cadia purpurea) has reverted to radially symmetrical flowers. Here, we investigate the genetic basis of this morphological reversal. Two orthologues of the floral symmetry gene CYCLOIDEA (CYC) demarcate the adaxial (dorsal) region of the flower in typical papilionoid legumes. In the model legume Lotus japonicus, one of these LegCYC genes has been shown, like CYC, to be required for the establishment of floral bilateral symmetry. This study shows that these genes are expressed in the adaxial region of the typical papilionoid flower of Lupinus, which belongs to the same papilionoid subclade as Cadia. In Cadia, these genes also are expressed, but the expression pattern of one of these has expanded from the adaxial to the lateral and abaxial regions of the corolla. This result suggests that the radial flowers of Cadia are dorsalized and, therefore, are not a true evolutionary reversal but an innovative homeotic transformation, where, in this case, all petals have acquired dorsal identity. This study raises a question over other putative reversals in animals and plants, which also may be cryptic innovations.
  Proceedings of the National Academy of Sciences 09/2006; 103(32):12017-20. · 9.68 Impact Factor
• Article: Heterogeneous selection on LEGCYC paralogs in relation to flower morphology and the phylogeny of Lupinus (Leguminosae).

  Richard H Ree, Hélène L Citerne, Matt Lavin, Quentin C B Cronk
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  ABSTRACT: An analysis of the molecular evolution of two LEGCYC paralogs in Lupinus (Genisteae: Leguminosae) reveals a varied history of site-specific and lineage-specific evolutionary rates and selection both within and between loci. LEGCYC genes are homologous to regulatory loci known to control floral symmetry and adaxial flower organ identity in Antirrhinum and its relatives. Within Lupinus, L. densiflorus is unusual in having flowers with a proportionally smaller standard (upright adaxial petals) and larger wings (lateral petals) than other lupin species. Phylogenetic estimates of the nonsynonymous/synonymous substitution rate ratio, omega, suggest that along the L. densiflorus lineage, positive selection (omega > 1) acted at some codon sites of one paralog, LEGCYC1B, and greater purifying selection (omega < 1) acted at some sites of the other paralog, LEGCYC1A. Overall, LEGCYC1A appears to be evolving faster than LEGCYC1B, and both paralogs are evolving faster than the internal transcribed spacer (ITS) region of nr DNA. The predominant historical pattern inferred is a highly heterogeneous "selectional mosaic" which we suggest may be typical of the teosinte branched 1-cycloidea-PCF (TCP) class of transcriptional activators, and possibly other genes. Codon models that do not account for both site-specific and lineage-specific variation in omega do not detect positive selection at these loci. We suggest a modification of existing branch-site models involving an additional omega parameter along the foreground branch, to account for the effects of both greater positive selection and greater purifying selection at different codon sites along a particular branch. The higher rates of evolution and congruent phylogenetic signal of both LEGCYC paralogs show promise for the use of these genes as markers for phylogeny reconstruction at low taxonomic levels in Genisteae [corrected]
  Molecular Biology and Evolution 02/2004; 21(2):321-31. · 5.55 Impact Factor
• Article: A phylogenomic investigation of CYCLOIDEA-like TCP genes in the Leguminosae.

  Hélène L Citerne, Da Luo, R Toby Pennington, Enrico Coen, Quentin C B Cronk
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  ABSTRACT: Numerous TCP genes (transcription factors with a TCP domain) occur in legumes. Genes of this class in Arabidopsis (TCP1) and snapdragon (Antirrhinum majus; CYCLOIDEA) have been shown to be asymmetrically expressed in developing floral primordia, and in snapdragon, they are required for floral zygomorphy (bilaterally symmetrical flowers). These genes are therefore particularly interesting in Leguminosae, a family that is thought to have evolved zygomorphy independently from other zygomorphic angiosperm lineages. Using a phylogenomic approach, we show that homologs of TCP1/CYCLOIDEA occur in legumes and may be divided into two main classes (LEGCYC group I and II), apparently the result of an early duplication, and each class is characterized by a typical amino acid signature in the TCP domain. Furthermore, group I genes in legumes may be divided into two subclasses (LEGCYC IA and IB), apparently the result of a duplication near the base of the papilionoid legumes or below. Most papilionoid legumes investigated have all three genes present (LEGCYC IA, IB, and II), inviting further work to investigate possible functional difference between the three types. However, within these three major gene groups, the precise relationships of the paralogs between species are difficult to determine probably because of a complex history of duplication and loss with lineage sorting or heterotachy (within-site rate variation) due to functional differentiation. The results illustrate both the potential and the difficulties of orthology determination in variable gene families, on which the phylogenomic approach to formulating hypotheses of function depends.
  Plant physiology 04/2003; 131(3):1042-53. · 6.53 Impact Factor
• Source

  Available from: oxfordjournals.org

  Article: Diversity of cycloidea -like Genes in Gesneriaceae in Relation to Floral Symmetry

  Hélène L Citerne, Michael Möller, Quentin C B Cronk
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  ABSTRACT: Homology assessment of cycloidea -like genes was carried out in Gesneriaceae, a predominantly zygomorphic family in which several independent reversals to actinomorphy have occurred, as a basis for further investigation of the control and evolution of floral symmetry. Phylogenetic analysis of Gesneriaceae cycloidea &lpar; Gcyc &rpar; suggests that independent duplication and gene loss events have occurred during the evolution of this family after the split from Scrophulariaceae. Comparison of Gcyc sequences between zygomorphic and naturally occurring actinomorphic taxa does not suggest that reversals to actinomorphy were caused in these cases by loss of function of cyc -like genes. Examination of floral development in the nearly actinomorphic Ramonda myconi did not reveal any evidence of residual unequal dorso-ventral differentiation indicative of expression of Gcyc . This suggests that Gcyc may be expressed before primordia initiation in R. myconi , or may have additional functions not directly related to floral symmetry. Copyright 2000 Annals of Botany Company