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SEPALLATA 3 Genes: Molecular Evolution and Development of Grass Flowers Lori Glenwinkel

SEPALLATA 3 Genes: Molecular Evolution and Development of Grass Flowers Lori Glenwinkel Advisor: Simon Malcomber, Plant Evolution Lab. Overview. -Overview of Grass flower morphology -Floral organ identity and the evolution of the Grass flower -SEPALLATA3 genes and floral organ developent

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SEPALLATA 3 Genes: Molecular Evolution and Development of Grass Flowers Lori Glenwinkel

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  1. SEPALLATA 3 Genes: Molecular Evolution and Development of Grass Flowers Lori Glenwinkel Advisor: Simon Malcomber, Plant Evolution Lab

  2. Overview -Overview of Grass flower morphology -Floral organ identity and the evolution of the Grass flower -SEPALLATA3 genes and floral organ developent -Prelimary Data pinpointing the SEP3 duplication event in the grasses SEP3 expression and the evolution of the lodicule -Molecular Evolution of duplicate Genes(Current and future projects) Positive selection analysis Noncoding regulatory region analysis of SEP3 genes

  3. Zanis 2007

  4. wo Two structures may be considered homologous if they are connected by a series of transitional forms (Whipple 2007)

  5. SEPALLATA Genes were first characterized in Arabidopsis sep1sep2sep3sep4 quadruple mutant Malcomber 2005 SEPALLATA genes encode MADS box Transcription factors Homeotic family of transcription factors required for vegetative and reproductive development SEPALLATA genes interact with B and C class transcription factors to specify the inner three whorls (carpels, stamen, lodicules)

  6. (Malcomber and Kellogg 2005) SEP3A and SEP3B, a grass specific Duplication?

  7. Pinpointing the SEP3 Duplication Event

  8. AP3 and PI are B class Heterodimers known to interact with SEPALLATA3 genes in Arabidopsis (Takashi 2001)

  9. WSEP Shitsukawa 2007

  10. Models of Duplicate Gene Evolution: New and Old Paradigm: one of the duplicates is either lost (pseudogenization) or gains a new function (neofunctionalization) • Problems with this model: • deleterious mutations are more probable than advantageous mutations • fails to account for the preponderance of retained duplicates in whole genomes Moore 2005

  11. Models of Duplicate Gene Evolution: New and Old Newer Subfucntionalization Model: duplicate genes acquire debilitating yet complementary mutations that alter one or more subfunctions of the single gene progenitor Strengths of this Model: does not rely on the sparse occurrence of beneficial mutations, but on more frequently occurring loss-of-function mutations in regulatory regions Moore 2005

  12. Investigating SEP3A and SEP3 genes for subfuctionalization rVISTA and Expression analysis • rVISTA, online program for comparing noncoding regulatory sequenced for conserved and non conserved TFBSs. • - Collect genomic sequences for grasses with enough of their genome sequenced. • - Search TRANSFAC database using rVISTA • Expression analysis: isolating SEP3A and SEP3B from disparate grass species, comparing expression between the lineages Significance: If differential regulation is established, a role for SEP3A and SEP3B in the development and evolution of the grass flower will be better understood.

  13. Investigating Neofunctionalziation Model in SEP3A and SEP3B lineages, PAML (Positive selection Analysis using Maximum Likelihood) PAML uses increasing complex models of evolution to estimate whether positive selection is acting on an amino acid site Ratio of nonsynonymous (n) to synonymous (s) mutations used to predict amino acid site changes in a lineage over time. dn/ds >1 indicates positive selection (suggests neofunctionalization) dn/ds <1 indicate negative selection dn/ds = 1 neutral selection Significance: If positive selection is acting on the SEP3A or SEP3B lineages,or at the base of the two clades, then neofunctionalization is suggested lending support to a role for the evolution of the grass spikelet.

  14. Conclusions Preliminary studies SEP3A/SEP3B duplication occurred prior to the evolution of the spikelet clade (indicating it may contribute to the unique grass flower morphology) SEP3 genes may have played a role the evolution of the lodicules. (SEP3A and B class gene expression) Future projects Molecular evolution analysis may suggest Subfunctionalization or Neofunctionalization fates for the SEP3 dupliate genes in the grasses. A strong case for SEP3A and SEP3B’s role in the evolution of the lodicules will result in a better understanding of how grass flower develop. This has potential value agriculturally considering that crop yeild is proportional to flower size.

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