Transcript Intro to grass flowers

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
-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
Zanis 2007
wo
Two structures may be considered
homologous if they are connected
by a series of transitional forms
(Whipple 2007)
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)
(Malcomber and Kellogg 2005)
SEP3A and
SEP3B,
a grass specific
Duplication?
Pinpointing the SEP3 Duplication Event
9
AP3 and PI are B class Heterodimers known to interact with SEPALLATA3 genes in Arabidopsis
(Takashi 2001)
WSEP
Shitsukawa 2007
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
•
Moore 2005
fails to account for the preponderance of retained duplicates
in whole genomes
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
Investigating SEP3A and SEP3 genes for
subfuctionalization
rVISTA and Expression analysis
rVISTA, online program for comparing noncoding regulatory
sequenced If
fordifferential
conserved andregulation
non conservedisTFBSs.
Significance:
established,
Collect genomic
sequences
grasses
with enough of
a role for•- SEP3A
and SEP3B
inforthe
development
their genome sequenced.
and evolution of the grass flower will be better
- Search TRANSFAC database using rVISTA
understood.
Expression analysis: isolating SEP3A and SEP3B from
disparate grass species, comparing expression between the
lineages
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
Significance: If positive selection is acting on the SEP3A or
lineages,or(n)
atto
the
base of the (s)
twomutations
clades, then
Ratio ofSEP3B
nonsynonymous
synonymous
used to predict amino acid
neofunctionalization
is
suggested
lending
support
to
a role for
site changes in a lineage over time.
the evolution of the grass spikelet.
dn/ds >1 indicates positive selection (suggests neofunctionalization)
dn/ds <1 indicate negative selection
dn/ds = 1 neutral selection
• 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.