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Adopting an integrative biology approach to dissect phytohormone regulated root growth

Reference	BB/D522603/1
Principal Investigator / Supervisor	Professor Malcolm Bennett
Co-Investigators / Co-Supervisors	Dr Susana Ubeda-Tomas
Institution	University of Nottingham
Department	Sch of Biosciences
Funding type	Research
Value (£)	223,089
Status	Completed
Type	Research Grant
Start date	01/10/2005
End date	31/03/2009
Duration	42 months

Abstract

Genetic studies have revealed that at least 5 different classes of phytohormones are required to regulate growth processes in plants. Unravelling how these phytohormone signals interact to control organ growth represents a key challenge for Plant Science research. Unlike previous genetic approaches, this study embraces an Integrative Biology approach which endeavours to develop a deeper understanding of how phytohormone signalling networks interact at the cellular/tissue level to regulate Arabidopsis root growth. The experimental programme aims to identify which root tissue(s) perceive each of the 5 phytohormones that control root growth in Arabidopsis. To achieve this objective, we will examine the growth effect(s) caused by blocking the sensitivity of a root tissue(s) towards an individual phytohormone. Dominant mutant versions of signalling components specific for each phytohormone transduction pathway will be expressed in selected root tissues using a GAL4 based expression approach. As a proof of principle, we recently blocked the auxin response in selected root tissue(s) using axr3-1 which encodes a dominant mutant form of the auxin signalling component IAA17. This approach enabled us to successfully demonstrate that auxin negatively regulates root growth by inhibiting epidermal cell elongation [Swarup et al, submitted to Nature]. Our preliminary results (see case for support for further details) have enabled us to formulate an integrative model for phytohormone regulated root growth. Our model predicts that the epidermis serves to restrain the growth of the inner root tissues and that different classes of phytohormones either promote or integrate these opposing forces. The experimental resources described above will enable us to test the following key hypotheses in our integrative model: Phytohormones that negatively regulate root growth act by inhibiting epidermal cell elongation via auxin; GA promotes root growth in the epidermis and/or inner tissues; Brassinosteroids positively regulate root elongation by promoting growth of inner tissues.

Summary

Understanding how plant growth is controlled is central to our ability to enhance crop yield and hence maintain food production ahead of world population growth. Like humans, plant growth is regulated by a collection of different growth hormones. Recent research has discovered that at least 5 different types of hormones either function to promote or reduce the growth of organs like roots and shoots. Whilst we often know a great deal about how each individual hormone works, we know very little about how these different hormones interact to fine tune plant growth, which represents the focus of this research proposal. Plant organs like for example roots are made up of at least 5 different types of tissues. Simplistically, plants may need at least 5 different types of hormones to regulate the growth of each tissue. However, recent research in our laboratory suggests hormones that reduce root growth only block the outermost root tissue termed the epidermis which, acting like a sausage skin, restrains the growth of the inner root tissues. We predict that other hormones which promote root growth act either to relieve the restraint in the epidermis and/or accelerate the growth of the inner root tissues. Our research project is deigned to test our sausage skin model by identifying which root tissues respond to which hormone. The knowledge gained from this study will help scientists to manipulate plant growth and eventually, ultimately enhance crop yield.

Committee	Closed Committee - Plant & Microbial Sciences (PMS)
Research Topics	Plant Science
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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