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Origins of Multicellularity
Chlamydomonas
Gonium
Eudorina
Pleodorina
Pandorina
Volvox
Structural Progressions in Colonial Green Algae
“The Volvocine Lineage”
Alternation of Generations
Evolutionary
Emphasis on the
Diploid Soma
mitosis
Diploid (2n)
Phase
Fertilization
2n
sori
Meiosis
Ferns
Haploid (n)
Phase
2n
n
Mosses
mitosis
n
Arabidopsis thaliana
The Thale or
Mouse-Eared Cress
The
Arabidopsis
Life Cycle
Embryo (2n)
Ovule (n)
Pollen (n)
flowering
rosette growth
Nuclear
Genome
5 chromosomes
125Mb
(10x yeast)
14% transposable elements
25,500 genes
(4.5x yeast)
11,000 gene families
+79 (chloroplast)
+58 (mitochondrion)
COGs in the Genomics Wheel
ca 2000
Transformation
by Agrobacterium
the Crown Gall Bacterium
imbibition, vernalization -> radicle outgrowth
Germination
Shoot apex
hypocotyl
(note apical
Photomorphogenesis
(hook opening,
cotyledon greening)
Root
hairs
Root apex
elongation
hook)
Photomorphogenesis
Cryptochromes
and
Phytochromes
Three
Primary
Tissues
•Dermal
Epidermis
•Ground
General Tissue
•Vascular
Xylem
Phloem
Enhancer trap GUS construct
Topless-1 embryos
make an apical root
Plant
Embryogenesis
Shaping the Plant Cell
Cellulose Synthase
Complexes
Microtubules
Overlay
Meristems
Tunica
L3
Radial Zones
Layers
Organization
of Shoot
Meristems
L1/L2/L3 chimeras
Embryo/Seedling Mutants
Apical-basal mutations (b-e)
Radial symmetry
mutations (f,g)
Organogenesis mutations (h-j)
Axial Mutants
Cross section of root
Root Structure
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video
Root Hairs
microtubules
gl1
ttg
No
Leaf
Hairs
WT
But
Lots of
Roots!
Epidermal Fates
WT has
8 files of
root
hairs
GL2::GUS
expressed in
N cells
Root Hair
Specification
(
)
Day length and
Temperature
FL-T
leaf
phloem
apex
Florigen is the protein
encoded by the FL-T
locus; it is produced in
the leaves and moves
through the plant to the
meristems to transmits
the flowering response
through the plant
The
Flowering
Stimulus
FL-C
Conversion to
a Floral
Meristem
Vegetative meristem
Floral meristem identity genes
(Lfy, Ap1, Cal; Tfl)
Floral meristem
Mapping genes (define boundaries) (Su)
Floral organ identity (homeotic) genes (whorl identity)
Sepals (Ap2)
Petals (Ap2, Ap3, Pi)
Stamens (Ap3, Pi, Ag)
Carpels (Ag)
stigma,
carpels
The ABC Model
of Floral Whorl Identity
B (Ap3, Pi)
A (Ap2)
Sepals
ap2
C (Ag)
Petals
pi
Stamens
Carpels
ag
A Few Questions for Thought
•Explain the evolutionary origins of multicellular
organisms. What are the benefits and costs of
multicellularity?
•Compare and contrast plant and animal (drawing upon
your own general knowledge) body plans.
•Describe how a new plant is formed during
development (from fertilization through germination).
•What are meristems, and why are they important in
plant biology?
•What are the three primary tissues of the plant body?
•What is the difference between a shoot and a root
meristem? Between a vegetative and a floral meristem?
•How are organ identities in determined in the flower?
What are the role(s) of homeotic genes in this process?