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Title: Spatial regulation of Rho GTPase signalling during root hair development in Arabidopsis thaliana is reliant upon the guanine nucleotide dissociation inhibitor SCN1
Author: Smallman, Matthew John
ISNI:       0000 0004 2674 9781
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2008
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The scn1-1 mutants of Arabidopsis are characterised by spatially deregulated sites of root hair growth. This studydemonstrates that this phenotype is the result of the loss of regulation of members of the plant specific sub-family of Rho small GTPases by the Guanine nucleotide Dissociation Inhibitor (GDI), encoded by SCN1. The small GTPases R0P2, R0P4 and R0P5 of Arabidopsis are members of the I subset of type I ROPs that terminate with a conserved CXXL box and undergo 3 prenylation. These small GTPases are expressed in trichoblasts, and localize in patters suggestive of specific roles throughout root hair development. Loss-of function ROP2, R0P4 or ROP5 mutants display distinct root hair phenotypes lending support to the hypothesis that : R0P2, R0P4 and ROP5 control the establishment of the site of root hair initiation and subsequent tip-growth. Our findings also reveal SCNl/GDIl and R0P2 co-localize in a similiar pattern in developing root hairs in planta, but SCNl/GDIl is able to associate directly with ROP2, ROP4 and ROP5 in vitro.This suggests root hair morphogenesis relies on the negative regulation of ROP activity by SCNl/GDI 1 and is further supported by morphological phenotypes of scnl-l plants which can be rescued by the over expression of CFP:GD11 fusion placed under the control of the root hair specific PRP3 (Proline Rich Protein3) promoter. These observations imply that ROPs can be selectively sequestered away from the from plasma membrane of elongating root hairs during tip growth thereby promoting growth along a planar axis. Differences in the observed binding affinity of R0P2 in comparison to R0P4 and ROPS for SCNl/GDIl provides evidence that the CXXL box may play a critical role in ROP regulation, and that R0P2 and R0P4 are differentially prenylated.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available