Unravelling the regulatory network controlling lateral root hydropatterning

Banda, Jason (2021) Unravelling the regulatory network controlling lateral root hydropatterning. PhD thesis, University of Nottingham.

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The 3-dimensional shape of a root system is of crucial importance to its ability to take up nutrients and water. As these resources are heterogeneously distributed in the soil, plants need to adapt their root growth to aid foraging. One such adaptive response is termed lateral root (LR) hydropatterning where roots branch towards areas with higher water availability.

The main aim of this thesis is to investigate how plant roots sense water distribution and which regulatory pathways control lateral root branching towards available water using the model plant Arabidopsis thaliana. We observed that the choice of lateral root founder cells (LRFC) in the pericycle cell layer they originate from is influenced by external water availability. This allows lateral roots to angle towards water from the very first round of formative cell divisions. Additionally, the emerging lateral root primordium grows towards water availability through asymmetric rounds of cell division in its primordium flanks.

LR hydropatterning is genetically regulated through a major regulator of LR initiation AUXIN RESPONSE FACTOR7 (ARF7). Knock-out mutants lose the ability to branch towards water and do not asymmetrically express the key transcription factor LBD16-GFP, a direct target for ARF7. This mechanism is regulated through post-translational regulation of ARF7. The ARF7 sequence contains four sites that can be SUMOylated. Transgenic lines expressing ARF7 with mutations in each of these four SUMO sites cannot rescue arf7-1 LR hydropatterning, revealing a key role for SUMOylation controlling water sensing by roots.

ARF7 SUMO status appears to be controlled by SUMO protease OVERLY TOLERANT TO SALT1 (OTS1). Double knock-out mutants in OTS1 and its close homolog OTS2 have severely delayed root development and a LR hydropatterning defect. Additionally, ots1 ots2 mutants display reduced LR initiation and emergence defects that can be restored to Wild-Type levels by expressing an OTS1-Venus transgene. OTS1-Venus can be detected from the late elongation zone onwards in root pericycle cells and is stably expressed in the primordia. However, no asymmetrical localisation of OTS1-Venus is observed after a hydropatterning cue suggesting that SUMO protease activity, rather than stability, controls LR hydropatterning. This thesis highlights the early response of lateral roots to asymmetrical water distribution and role the deSUMOylation machinery plays in its molecular regulation.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Bennett, Malcolm J.
Bishopp, Anthony
Keywords: Root development, Root water sensing, Hydropatterning, SUMOylation
Subjects: Q Science > QK Botany
S Agriculture > SB Plant culture
Faculties/Schools: UK Campuses > Faculty of Science > School of Biosciences
Item ID: 65859
Depositing User: Banda, Jason
Date Deposited: 06 Oct 2023 08:48
Last Modified: 07 Oct 2023 04:30
URI: https://eprints.nottingham.ac.uk/id/eprint/65859

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