Environmental regulation of plant root development

Kilic, Azad (2022) Environmental regulation of plant root development. PhD thesis, University of Nottingham.

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Soil compaction represents a major agronomic challenge, inhibiting root growth and resource capture, causing significant yield losses. Roots employ ethylene to sense soil compaction as its reduced air space causes this gaseous signal to accumulate around root tips (Pandey et al., 2021). One of the key aims of Chapter 2 is to investigate the underlying hormonal signals and regulatory genes that control compaction resistance in tomato. The aims will be achieved by exploiting prior knowledge gained from the model plants and crops (i.e., Arabidopsis, rice, and maize). My results reveal that during soil compaction stress tomato roots employ the volatile hormone signal ethylene to promote root growth inhibition. For example, less ethylene-sensitive tomato lines were observed to exhibit root growth resistance to compaction stress. The aim of my thesis objective is to identify the underlying genes that control root penetration to provide a mechanistic understanding of root-determined processes that influence traits within and beyond the root. This knowledge can be vital for longer-term breeding strategies to deliver novel varieties into commercial practice.

Hormone signals like ethylene have recently been reported to play a critical role in soil compaction responses in crops like rice (Pandey et al., 2021). Ethylene is likely to employ other downstream signals to mediate these compaction responses like cortical radial cell expansion. Rice roots grown in compacted soil conditions exhibit elevated levels of the signal abscisic acid (ABA). In Chapter 3, I explore the role of ABA during rice root compaction responses. My results reveal that soil compaction inhibits rice root growth by increasing the ethylene response, which then upregulates several abscisic acid (ABA) biosynthesis genes. Testing the functional importance of their upregulation revealed mutations in rice ABA biosynthetic genes like OsMHZ5 disrupt radial cortical expansion in compacted soil, suggesting ABA acts downstream of ethylene to control this adaptive response.

Water stress regulates several root adaptive responses including compaction (focus of Chapter 3). In Chapter 4, I investigate how water stress controls lateral root outgrowth. Lateral root branching and length play essential roles during adaptation to water stress. To identify potential regulators of this adaptive process, GWAS predictions on a root phenotype dataset generated for a maize diversity panel subjected to water stress were analysed. One promising loci predicted by GWAS encoded a suberin synthesis gene. I tested the impact of a loss-of-function mutant allele in Arabidopsis, which exhibited significantly higher lateral root (LR) length compared to wild-type (WT; Col-0). Moreover, mutant roots display a similar longer lateral root phenotype as suberin degradation line pCASP1::CDEF, suggesting there is a link between root surface area and suberin-based water-impermeable barrier formation in roots. The spatial relationship between suberin biosynthesis and lateral root development under environmental stress conditions awaits expressing these transgenic lines in a mutant background.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Bennett, Malcolm J.
Seymour, Graham B.
Fray, Rupert
Keywords: Tomato, Rice, Soil, Root architecture, Ethylene, ABA, Suberin
Subjects: Q Science > QK Botany > QK640 Plant anatomy
Faculties/Schools: UK Campuses > Faculty of Science > School of Biosciences
Item ID: 68891
Depositing User: KILIC, Azad
Date Deposited: 03 Aug 2022 04:40
Last Modified: 16 Aug 2022 14:16
URI: https://eprints.nottingham.ac.uk/id/eprint/68891

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