Research Article: A Theoretical Model for ROP Localisation by Auxin in Arabidopsis Root Hair Cells

Date Published: December 16, 2009

Publisher: Public Library of Science

Author(s): Robert J. H. Payne, Claire Suzanne Grierson, Henrik Jönsson.

Abstract: Local activation of Rho GTPases is important for many functions including cell polarity, morphology, movement, and growth. Although a number of molecules affecting Rho-of-Plants small GTPase (ROP) signalling are known, it remains unclear how ROP activity becomes spatially organised. Arabidopsis root hair cells produce patches of ROP at consistent and predictable subcellular locations, where root hair growth subsequently occurs.

Partial Text: Rho small GTPases are a large family of highly conserved signalling proteins that contribute to biological processes as diverse as host-pathogen interactions, wound healing, development, and cancer [1], [2]. They play fundamental roles in eukaryotic cell division, cell morphogenesis and cell movement, through effects on actin and microtubule cytoskeletons, gene expression, and enzyme activity. The intracellular location of these proteins is important, and in plants the active forms of certain Rhos accumulate in patches that induce local cell outgrowths. Activation of the Rho-of-Plants (ROPs) proteins may occur by transcriptional up-regulation of ROP expression, or by the modulation of ROP activity via ROP-regulators (including ROP-GEFs and ROP-GAPs) that might themselves be transcriptionally or post-transcriptionally regulated [3], [4]. One of the best systems for studying ROP activity is the developing root hair (RH) cell.

Our in silico experiments shed light on the possible role of auxin in the development of root hairs. Although the mechanisms by which auxin influences ROP activity are not known, our results are strongly supportive of the hypothesis that a cellular auxin gradient upregulates the net amount of active ROP. The kinetics of ROPs are less well characterised than those of Rhos, and so our model is necessarily kept simple. It is a strength of the model that, despite this, it is able to mimic the ROP localisation patterns of such a range of root hair mutants and transgenic lines. In doing so, our model provides a valuable bridge between the genetics, molecular biology, and mutant phenotypes of root hair morphogenesis.



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