Roberts, Jemma (2022) Characterisation of plant beneficial effectors from the mutualist, Serendipita indica. PhD thesis, University of Warwick.

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Abstract

The root and shoot systems of plants are in constant contact with a plethora of microbe species. Some of these microbes are disease causing pathogenic microbes and some are mutualistic, benefiting the host plants’ growth. All microbes secrete small proteins, termed effectors, into the host plant. These effectors are commonly used to subvert plant immune responses that attempt to cease colonisation of the microorganism. Effectors have been implicated in manipulation of many plant signaling cascades including the control of phytohormone signaling. Research into pathogenic species effectors is useful in conferring disease resistance. However, not all microorganisms are causative of disease, research into mutualist effectors and their functions on the host plant is limited. The endophyte Serendipita indica is a mutualist that confers many beneficial effects to the host plants. These include an increase in yield, abiotic tolerance, and biotic resistance. Effectors from S. indica are not well characterised and those that are generally function within the apoplastic space and not intracellularly on plant signaling. The effectors of S. indica may be causative of the beneficial effects we see when plants are colonised. This thesis aims to characterise S. indica effector candidates further and examine how they alter host plant signaling cascades. In studying the mechanisms by which S. indica effectors confer beneficial traits to the host plant, the results can be reproduced synthetically. In this way crops could be modified to enhance beneficial traits and improve crop productivity without the limitations of bio-controls. 150 S. indica effector candidates were characterised using several approaches. Investigation into cytokinin signaling was undertaken to understand how 20 selected S. indica effectors may be altering this phytohormonal pathway. Phenotypic analysis of root lengths and qPCR uncovered several S. indica effector candidates that alter cytokinin signalling. Split luciferase assays and affinity purification coupled mass spectrometry added confidence to interaction partners screened of two effector candidates. Root length assays of plants expressing effector candidates were screened for salt and drought tolerant traits. These combined experimental approaches identified an effector candidate (deemed SIE108) that had a unique plant target protein (RACK) not shared by other pathogens and that conferred salt and drought tolerance when over expressed within the host plant. This effector candidate and its plant target were further characterised using protein purification, structure prediction and further AP-MS experiments. The binding of SIE108 to plant target RACK proteins interfered with numerous proteins that would normally bind to RACK in control conditions. The conferment of drought and salt tolerance may be linked to a specific phosphorylation site of RACK that SIE108 interferes with. This information can be used to synthetically alter RACK or design applicable small molecules to confer drought and salt tolerance to plants without the limitations of added bio-controls.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QK Botany
Library of Congress Subject Headings (LCSH):	Roots (Botany), Plant-microbe relationships, Endophytes, Plant-fungus relationships, Cytokinins
Official Date:	February 2022
Dates:	Date Event February 2022 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	School of Life Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Crow, Allister ; Schäfer, Patrick ; Jones, Alexandra M.
Sponsors:	Biotechnology and Biological Sciences Research Council (Great Britain) ; BASF SE
Format of File:	pdf
Extent:	xi, 114 leaves : colour illustrations, charts
Language:	eng

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