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?

A developmental geneticist’s guide to roots

Integrative Biology Centre for Plant the

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

Shoot apical meristem produces the shoot, leaves, inflorescences and floral organs.

The root apical meristem produces just one organ: the root

Smith et al, PNAS 2006

A Developmental Biologists perspective: the root as a model organ

Roots exhibit a wide variety of forms

The model organism Arabidopsis

Tracing cell lineages in the root.

Cell types in the root

Xylem Transports water and minerals from root to shoot

We focus on just one cell type: protoxylem

Visualizing xylem cells Fuchsin highlights lignified tissue Toluidine Blue highlights the cell walls and cytoplasm

We focus on just one question: what controls the positioning of xylem cells?

Radial symmetry

Embryo

Bisymmetry

Growing root

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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

Mähönen, Bishopp et al. Science 2006

AHP6 gene activity ahp6 mutant

Another hormone (Auxin) promotes AHP6 expression

A protein PIN7 regulates the transport of Auxin

PIN7 is regulated by …….. Cytokinin

Cytokinin (hormone)

AHP6

Auxin (hormone)

PIN7

Muraro et al., 2014 PNAS

Mathematical model for vascular patterning

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Model predicts an additional cytokinin inhibitor is needed in the metaxylem for ARR5 patterning

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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.

Auxin response(DR5)

PIN7

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Cell types in the root

Integrative Biology Centre for Plant the

Why am I interested in xylem? Manipulation of xylem may affect water use efficiency in crops

Richards and Passioura, Aust. J. Agric. Res. 1989

Narrow xylem – 55 µm Unselected controls– 65 µm

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.

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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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