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Discovery focuses on the ‘point’ of plant cell development

16.12.2005


Scientists at the John Innes Centre (JIC), Norwich, UK[1], today report a breakthrough in understanding how plant cells control the direction of their growth. The report, in the international scientific journal Nature[2], describes a gene (called SCN1) which controls the activity of an enzyme that is critical to cell growth. The researchers have found that SCN1 keeps cell growth in check.



“This is an exciting discovery because the direction of cell growth is very important in determining the shape of plant cells and this controls the overall shape and structure of the plant”, says Professor Liam Dolan (project leader at JIC). “We already know about some of the processes involved in cell growth but this is a new insight into how they are localised so that cells can be made to grow in a particular direction”.

The researchers made their discovery from studies on root hair formation on roots of the model plant Thale Cress (Arabidopsis thaliana). Root hairs are important to the plant as they dramatically increase the surface area of the roots, providing a large surface through which water and minerals can be absorbed.


These hair cells are of interest to Dr Dolan’s group because of the way they develop from cells on the surface of the root. Initially a small bulge forms in the surface wall of a root cell and from this bulge a root hair develops. The hairs are long thin cells that grow away from the root surface by cell growth at their tip; the tip of the hair cell ‘pushes’ itself away from the root. To understand how cell growth is restricted to just the tip of the cell the scientists compared several mutant plants where hair development and growth was abnormal. In the plants with abnormal development they discovered that the processes needed for cell growth were not localised, consequently root cells could produce multiple root hairs and the root hairs had several growing tips.

They established that this unusual growth was the result of damage to a specific gene (SCN1). SCN1 produces an enzyme (AtrohGDI1) that inactivates another enzyme (AtrbohC) that promotes cell growth. In the mutants, were no AtrohGDI1 is produced, the cell growth enzyme AtrbohC is hyperactivated, and its activity is dispersed around the cell. Consequently, growth gets out of control resulting in the formation of weird cell shapes[3].

Professor Dolan concludes “experiments on the root hairs of the common weed Arabidopsis may seem bizarre but they are giving us valuable new insights into the sophisticated systems that all multicellular organisms such as plants, animals and fungi use to control their growth. The more we understand of how plants direct their development and eventual size, shape and structure, the greater the opportunities we have to breed plants that have been altered to perform better as crops or ornamentals”.

Notes:

1) The John Innes Centre (JIC), Norwich, UK is an independent, world-leading research centre in plant and microbial sciences. The JIC has over 800 staff and students. JIC carries out high quality fundamental, strategic and applied research to understand how plants and microbes work at the molecular, cellular and genetic levels. The JIC also trains scientists and students, collaborates with many other research laboratories and communicates its science to end-users and the general public. The JIC is grant-aided by the Biotechnology and Biological Sciences Research Council.

2) Nature can be contacted at: Nature London
Katharine Mansell, Tel:+44 (0)20 7843 4658; Fax:+44 (0)20 7843 4951
E-mail: k.mansell@nature.com
Sophie Hebden,
Tel: +44 (0)20 7843 4502; Fax:+44 (0)20 7843 4951
E-mail: s.hebden@nature.com
The paper referred to in this release is “A RhoGDP dissociation inhibitor spatially regulates growth of root hair cells. Rachel Carol et al. 2005 Nature”.

3) Root hair cells develop from epidermal root cells (called trichoblasts). Initially a bulge forms on the surface wall of the trichoblast and from this bulge a root hair develops. Root hair cell growth occurs at the tip; the tip of the hair cell ‘pushes’ itself away from the root as the cell elongates in a zone immediately behind the cell tip.

Plant cell growth requires production of reactive oxygen species (ROS) by RHD2/AtrbohC NADPH oxidase. The tip growth seen in root hair cells is correlated with the activity of RHD2/AtrbohC NADPH oxidase and ROS production, which is restricted to the cell tip.

In mutants where root hair development and growth was abnormal ROS production was not localised and this correlated with trichoblasts producing multiple root hairs and root hairs having several growth axis.

The mutated gene (SCN1 = SUPERCENTIPEDE1) encodes a RhoGTPase GDP dissociation inhibitor. SCN1’s enzyme product (AtrohGDI1) represses (inactivates) the AtrbohC NADPH oxidase that produces ROS critical for cell growth. AtrohGDI1 is a component of the mechanism that focuses/restricts AtrbohC NADPH oxidase activity to the cell tip.

Liam Dolan | alfa
Further information:
http://www.jic.ac.uk

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