Functional characterisation of Arabidopsis phototropin 1 in the hypocotyl apex

Sullivan, S., Takemiya, A., Kharshiing, E., Cloix, C., Shimazaki, K.-i. and Christie, J. M. (2016) Functional characterisation of Arabidopsis phototropin 1 in the hypocotyl apex. Plant Journal, 88(6), pp. 907-920. (doi: 10.1111/tpj.13313) (PMID:27545835) (PMCID:PMC5215551)

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Abstract

Phototropin (phot1) is a blue light-activated plasma membrane-associated kinase that acts as the principal photoreceptor for shoot phototropism in Arabidopsis in conjunction with the signalling component Non-Phototropic Hypocotyl 3 (NPH3). PHOT1 is uniformly expressed throughout the Arabidopsis hypocotyl, yet decapitation experiments have localised the site of light perception to the upper hypocotyl. This prompted us to investigate in more detail the functional role of the hypocotyl apex, and the regions surrounding it, in establishing phototropism. We used a non-invasive approach where PHOT1-GFP (P1-GFP) expression was targeted to the hypocotyl apex of the phot-deficient mutant using the promoters of CUP-SHAPED COTYLEDON 3 (CUC3) and AINTEGUMENTA (ANT). Expression of CUC3::P1-GFP was clearly visible at the hypocotyl apex, with weaker expression in the cotyledons, whereas ANT::P1-GFP was specifically targeted to the developing leaves. Both lines showed impaired curvature to 0.005 μmol m-2 s-1 unilateral blue light, indicating that regions below the apical meristem are necessary for phototropism. Curvature was however apparent at higher fluence rates. Moreover, CUC3::P1-GFP partially or fully complemented petiole positioning, leaf flattening and chloroplast accumulation, but not stomatal opening. Yet, tissue analysis of NPH3 de-phosphorylation showed that CUC3::P1-GFP and ANT::P1-GFP mis-express very low levels of phot1 that likely account for this responsiveness. Our spatial targeting approach therefore excludes the hypocotyl apex as the site for light perception for phototropism and shows that phot1-mediated NPH3 de-phosphorylation is tissue autonomous and occurs more prominently in the basal hypocotyl.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Cloix, Dr Catherine and Christie, Professor John and Sullivan, Dr Stuart
Authors: Sullivan, S., Takemiya, A., Kharshiing, E., Cloix, C., Shimazaki, K.-i., and Christie, J. M.
College/School:College of Medical Veterinary and Life Sciences > Institute of Cancer Sciences
College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Journal Name:Plant Journal
Publisher:Wiley
ISSN:0960-7412
ISSN (Online):1365-313X
Published Online:22 August 2016
Copyright Holders:Copyright © 2016 The Authors
First Published:First published in Plant Journal 88(6): 907-920
Publisher Policy:Reproduced under a Creative Commons License

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
581491Regulation of Auxin Fluxes Required For Phototropic GrowthJohn ChristieBiotechnology and Biological Sciences Research Council (BBSRC)BB/J016047/1RI MOLECULAR CELL & SYSTEMS BIOLOGY
659801Photoreceptor Engineering to Modulate Plant GrowthJohn ChristieBiotechnology and Biological Sciences Research Council (BBSRC)BB/M002128/1RI MOLECULAR CELL & SYSTEMS BIOLOGY