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Updated: Jul 19, 2026

Assaying Proteasomal Degradation in a Cell-free System in Plants
Published on: March 26, 2014
'Candidatus Phytoplasma mali' Genome Encodes a Protein that Functions as an E3 Ubiquitin Ligase and Could Inhibit
Alisa Strohmayer1, Mirko Moser2, Azeddine Si-Ammour2
1RLP AgroScience GmbH, AlPlanta-Institute for Plant Research, Breitenweg 71, 67435 Neustadt an der Weinstraße, Germany.
Abstract:
Phytoplasmas are the causative agent of numerous diseases of plant species all over the world, including important food crops. The mode by which phytoplasmas multiply and behave in their host is poorly understood and often based on genomic data. We used yeast two-hybrid screening to find new protein-protein interactions between the causal agent of apple proliferation 'Candidatus Phytoplasma mali' and its host plant. Here, we report that the 'Ca. P. mali' strain PM19 genome encodes a protein PM19_00185 that interacts with at least six different ubiquitin-conjugating enzymes (UBC; E2) of Arabidopsis thaliana. An in vitro ubiquitination assay showed that PM19_00185 is enzymatically active as E3 ligase with A. thaliana E2 UBC09 and Malus domestica E2 UBC10. We show that a nonhost bacteria (Pseudomonas syringae pv. tabaci) can grow in transgenic A. thaliana plant lines expressing PM19_00185. A connection of phytoplasma effector proteins with the proteasome proteolytic pathway has been reported before. However, this is, to our knowledge, the first time that a phytoplasma effector protein with E3 ligase activity has been reported.
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