the
Centre for Plant
Integrative Biology
A developmental geneticist’s guide to roots
Find out about the hidden half of plants
• What do roots look like from the inside?
• How do roots form?
• Can we improve root systems to increase food production?
What is developmental genetics?
How do multicellular organisms form?
• Preformation is the
idea that the egg or
sperm contains an
embryo
A preformed
miniature infant, or
“homunculus,” that
simply becomes
larger during
development
Figure 47.2
Developmental History of a Human
Plants can change their developmental programme depending
on environmental signals.
Plants have amazing regenarative abilities.
How do plants form?
Only the rudimentary plant axis is set up
during embryogenesis
Cotyledon
Shoot
apical
meristem
Root
apical
meristem
A Developmental Biologists perspective:
the root as a model organ
Shoot apical meristem produces the shoot, leaves,
inflorescences and floral organs.
Smith et al, PNAS
2006
The root apical meristem produces just one organ:
the root
Roots exhibit a wide variety of forms
The model organism Arabidopsis
Tracing cell lineages in
the root.
Cell types in the root
We focus on just one cell type: protoxylem
Xylem
Transports water
and minerals from
root to shoot
Visualizing xylem cells
Fuchsin highlights lignified tissue
Toluidine Blue highlights the cell walls and
cytoplasm
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Centre for Plant
Integrative Biology
We focus on just one question: what controls the positioning of xylem cells?
Bisymmetry
Radial symmetry
Embryo
Growing root
Be wary of what you read. DNA is not
really a blueprint.
DNA provides a set of instructions
whereby cells can self-organize
Central Dogma
Gene expression patterns in Fly embryos
Nikon handbook of microscopy
We look for mutants affecting xylem patterning.
The first one to be found was called wooden leg (wol)
Mähönen et al. Genes & Dev 2000
WOL encodes a Cytokinin
(Hormone)Receptor
Hormone made in one
cell
Hormone moves to
adjacent cells/tissues
Hormone elicits a
response in these cells
Altering levels of cytokinin signalling affect
differentiation of protoxylem
Reduced
cytokinin
signalling
Increased
cytokinin
signalling
A protein AHP6 “switches off” cytokinin at the
protoxylem position
AHP6 gene activity
ahp6 mutant
Mähönen, Bishopp et al. Science 2006
Another hormone (Auxin) promotes AHP6 expression
A protein PIN7 regulates the transport of Auxin
PIN7 is regulated by …….. Cytokinin
Auxin (hormone)
PIN7
AHP6
Cytokinin (hormone)
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Centre for Plant
Integrative Biology
Mathematical model for vascular patterning
Muraro et al., 2014 PNAS
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Centre for Plant
Integrative Biology
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Centre for Plant
Integrative Biology
Model predicts an additional cytokinin inhibitor is needed in the
metaxylem for ARR5 patterning
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Centre for Plant
Integrative Biology
Auxin response(DR5)
PIN7
Spread of PIN7 to all of stele bar the metaxylem is predicted by the model when SHR / miRNA is removed.
This is also seen experimentally in the shr k.o. mutant.
Cell types in the root
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Centre for Plant
Integrative Biology
Why am I interested in xylem?
Manipulation of xylem may affect water use efficiency in crops
Narrow xylem – 55 µm
Unselected controls– 65 µm
Richards and Passioura, Aust. J. Agric. Res. 1989
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Centre for Plant
Integrative Biology
Work in Nottingham by Malcolm
Bennett, Ranjan Swarup and Ive
de Smet’s groups is uncoupling
the regulatory mechanisms
controlling root architecture.
Development of microCT
imaging(Sacha Mooney) allows
visualization of roots in soil.
Sacha Mooney
Root hairs increase the surface area of roots enhancing water and nutrient
uptake.
Savage N, Yang TJW, Chen CY, Lin K-L, et al. (2013) PLoS ONE 8(10): e75452. doi:10.1371/journal.pone.0075452
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