Functional and structural analysis of a fungal effector and its host target at plasmodesmata

Turley, Emma K. (2025) Functional and structural analysis of a fungal effector and its host target at plasmodesmata. Doctoral thesis, University of East Anglia.

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Abstract

To establish infection, phytopathogens deploy effector proteins to modify the plant intracellular environment and compromise host defences. Across diverse pathosystems, host proteins with heavy metal-associated (HMA) domains have been repeatedly identified as binding partners of effectors, as well as determinants of infection success. However, the endogenous functions of HMA proteins, including their roles in plant defence, are not well understood.

In this work, I show that ChEC108, a putative secreted effector from the anthracnose fungus, Colletotrichum higginsianum, binds a tandem HMA domain-containing protein from Arabidopsis thaliana called HIPP6. To better understand why HMA proteins are frequently targeted by pathogens, I sought to structurally and functionally characterise the ChEC108-HIPP6 complex.

Using X-ray crystallography, I discovered that ChEC108 is capable of binding either of the HIPP6 HMA domains via a near-identical mechanism, involving coordination of a metal ion at the binding interface. In planta, both ChEC108 and HIPP6 localise to plasmodesmata, and ChEC108 exploits these membrane-lined channels to move between cells. Although I initially hypothesised that ChEC108 might function as a virulence factor, exploiting HIPP6 to promote its intercellular movement, I observed that the effector was dispensable for fungal virulence and remained cell-to-cell mobile even in the absence of HIPP6, suggesting other host factors must facilitate its trafficking. Despite numerous HMA proteins being previously implicated as susceptibility factors in an infection context, my data suggest HIPP6 is more likely to positively regulate defensive processes upon ChEC108 binding. Metal-binding residues of the HIPP6 HMA domains are critical for both plasmodesmal localisation and complex formation with ChEC108, yet the functional implications of HIPP6-metal association are currently unknown.

These findings have uncovered potential new roles for HMA proteins in plasmodesmata-localised signalling during fungal infection, while raising questions surrounding the function of metal-binding proteins at plasmodesmata and in plant immunity more generally.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Chris White
Date Deposited:	29 Jan 2026 09:32
Last Modified:	29 Jan 2026 09:32
URI:	https://ueaeprints.uea.ac.uk/id/eprint/101784
DOI:

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