The biochemical basis of plant ATG8 substrate specificity

Zess, Erin (2019) The biochemical basis of plant ATG8 substrate specificity. Doctoral thesis, University of East Anglia.

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Autophagy is an essential eukaryotic cellular quality control pathway that involves the degradation of self- and non-self macromolecules , with multiple layers of specificity defining the dynamics of substrate uptake, sub-cellular trafficking, and turnover. ATG8 is a highly-conserved ubiquitin-like protein that is central to the selectivity of the autophagy pathway, directly or indirectly binding desired autophagic cargo. Throughout plant evolution, ATG8 has expanded from a single protein in algae to multiple isoforms in higher plants. However, the degree to which ATG8 isoforms have functionally specialized to bind distinct proteins is unclear. In this thesis, I described the potato ATG8 interactome using in planta immunoprecipitation followed by mass spectrometry, discovering that potato ATG8 isoforms bind distinct sets of plant proteins with varying degrees of overlap. In addition, I defined the biochemical basis of potato ATG8 specialization. I revealed that the ATG8 N-terminal β-strand underpins binding specificity to substrates that contain ATG8-interacting motifs (AIMs), including the ATG8targetting effector from the potato late blight pathogen Phytophthora infestans, PexRD54. To approach the question of ATG8 substrate specificity from the opposing direction, I also explored the evolutionary dynamics of PexRD54 in different host-specific lineages of Phytophthora. I found that the PexRD54 ortholog from P. mirabilis, a closely related species to P. infestans, has a polymorphism in its AIM which nearly abolishes binding to the ATG8s of its host, Mirabilis jalapa. These results provide insights into the requirements of a functional ATG8-interacting motif, as well as raise questions as to whether specific selective pressures of the M. jalapa host environment have shaped the evolution the P. mirabilis PexRD54.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Katherine Whittaker
Date Deposited: 14 Feb 2020 09:26
Last Modified: 14 Feb 2020 09:26

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