Evodevo:

1
Plant evo-devo and floral evolution

• Evo-devo
• studies how the dynamics of development determine
  the phenotypic variation arising from genetic
  variation and how that affects phenotypic
  evolution.

2
Evo-devo and plants

• Homology - structures have the same genetic and
  developmental basis
• Gene duplication
• Epigenetics
• Regulatory changes versus amino acid changes
• Mutations of large versus small effect

3
Plants versus animals

• Modular (indeterminate) growth
• Alternation of generations
• cpDNA
• Cell wall/no distinction between germ line and
  soma

4
Green plant phylogeny
5
Alternation of generations key to the evolution
of land plants
Liverwort sporophyte
Liverwort gametophyte
6
Double fertilization and imprinting in angiosperms
FERTILIZATION INDEPENDENT SEED
mutations allow seeds to develop in the absence
of fertilization Gymnosperms produce wasteful
structures even if fertilization does not
occur Genes are imprinted and paternal copy not
expressed
7
Major innovations during plant evolution
Unicellular-gtfilamentous-gt parenchymatous cell
division
Cuticle and stomata Protection of
spores Conductive tissue Heterospory
Leaf evolution Root evolution Thickening of
stems Seed evolution
Male and female sporangia -gtcosexual
structure Closed carpels (SI) Zygomorphy
8
Leaf evolution and development
Leaf arose 6 times independently (mosses,
liverworts, ferns, horsetails and seed
plants) Evolved from indeterminate lateral
branching systems but now are determinant
structures KNOX genes maintain indeterminate
meristematic growth Determinate growth in leaves
(indeterminate growth-KNOX-is suppressed by
PHAN/RS2/AS1) Many other changes involved in
leaf evolution (e.g. dorsoventrality - PHB)
9
Leaf evolution and gene duplication
KNOX genes are present in moss (ancient
duplication)
Important for organized meristem- characteristic
of land plants
10
The evolutionary fate of duplicate genes
Moore and Purugganan 2005
11
Flower evolution zygomorphy is a key innovation
Zygomorphy (bilateral symmetry)
Kay et al 2006
12
Zygomorphy and and gene duplication
Regulated by two related TCP/R transcription
factors, CYCLOIDEA and DICHOTOMA Bee pollination
selected for maintenance and divergence in
function of these duplicated genes
13
The evolution of multi-gene families
Gene duplication has lead to the evolution of
large multi-gene famlies (e.g. MYB transcription
factors) MYB family very large in plants but
small in animals. Why? MYB transcription factors
might be prone to assuming new expression patterns
14
Flower evolution and zygomorphy
Members of the MYB transcription family (RAD and
DIV) are also involved in floral symmetry RAD is
activated my CYC and DICH and helps establish
adaxial flower identity and DIV is involved in
abaxial flower identity
Kalisz et al 2006
15
Flower evolution MADS-boxes genes
Overlapping expression of MADS-box transcription
factors Same control for all eudicots for
stamens (homologous) but not petals
(non-homologous)
16
Flower evolution MADS-boxes genes and CMS
Chase 2006
17
Flower evolution and low copy number genes
LEAFY (LFY) specifies floral meristem identity
and controls expression of MADS-box transcription
factors Low copy number-duplication disrupt
precise function?
18
The mostly male hypothesis the origin of the
co-sexual flower
LFY is single copy in angiosperms but double copy
in gymnosperms Gene phylogeny indicates that the
paralogy occurred before the divergence of
angiosperms
19
The mostly male hypothesis the origin of the
co-sexual flower
20
The mostly male hypothesis the origin of the
co-sexual flower
Paralogs in pine are PRFLL (Pinus radiata
FLORICAULA/LEAFY-like) highly expressed in male
cones NEEDLY highly expressed in female
cones Angiosperms have lost the NEEDLY
paralog in Arabidopsis, LYF mutants lack stamens
21
The mostly male hypothesis the origin of the
co-sexual flower
Angiosperms have cosexual flowers
(ancestrally) Gymnosperms have separate male and
female reproductive structures (back to the
Devonian) NEEDLY (female lost)
ectopic ovules
22
The Doebley hypothesis
Mutations in regulatory genes (particularly
cis-regulatory region of these genes) are less
likely to be pleiotropic than signaling/structural
genes and thus more likely to result in adaptive
evolutionary change e.g. positive selection in
NTR TB1 in maize Controversial hypothesis
Hoekstra (2007) -Gene duplication can ameliorate
the negative pleiotropic effects -Many more
studies have identified adaptive changes in
protein sequence (but perhaps easier to
detect) -More data is needed
23
Mode and tempo of evolution

• Neo-Goldschmitian view of evolution (the hopeful
  monster)-mutations of large effect
• Neo-Darwinian view of evolution-many mutations of
  small effect

24
Mode and tempo of evolution

• drastic morphological change can require
  surprisingly little genetic change
• examples include flowering time in Arabidopsis
  FRIGIDA
• visualized as jumps from peak to peak on an
  adaptive landscape

25
Flower colour cline in Antirrhinum
26
The genetic basis of natural variation in flower
colour in Antirrhinum
ROS el/ROS el SULF/SULF
ros EL/ros EL sulf/sulf
27
The genetic basis of natural variation in flower
colour in Antirrhinum
F2 cross between striatum and pseudomajus
sulf/sulf
SULF/___
ros EL/ros EL
ROS el/ROS el
Yellow largely controlled by SULF locus Magenta
largely controlled by ROS and EL loci
28
Flower colour in Antirrhinum
29
Molecular variation at flower colour locus ROS1
and a linked locus
PAL is not associated with flower colour
suggesting gene flow between subspecies ROS1
associated with flower colour indicating
selection is maintaining the flower colour cline
30
Clinal variation at flower colour locus ROS1 and
two linked loci
ROS1
DICH
PAL
31
Clinal variation at flower colour locus ROS1 and
two linked loci
ROS1 mirrors flower colour cline while DICH and
PAL do not indicating selection is maintaining
the flower colour cline
32
Adaptive ridges?
Flower colour of other species can be placed the
the genotypic space Suggest evolve yellow and
red following ridge, not through orange colour