Interrupting virus replication
How blocking interaction of a virus protein with plant proteins stops virus reproduction
Just like us humans, plants are also infected by viruses. These can cause lots of damage. Therefore, researchers like to know how these viruses work, so they can stop them where possible.
One of those damaging viruses is the tomato yellow leaf curl virus. This virus and others from the same group manipulate the infected plants so that it reproduces their DNA. One crucial protein for this is: Rep. Rep recruits host proteins that its needs for the reproduction of its DNA. Rep does this through manipulation of the signals that proteins give each other.
A new study by Dutch researchers analysed how Rep does this. The first thing they did was testing which plant proteins interact with Rep. This they first did through an assay in yeast, followed up by an assay in plants whereby they gave Rep and its potential binding proteins each one half of a fluorescent protein. Only when Rep and the potential binding protein were so close that they most probably bind, then the two halves of the fluorescent protein came together and did the fluorescent protein light up.
Binding via SIM motif
For both assays the researchers observed that Rep binds to SUMO1 and SCE1. Both SUMO1 and SCE1 are involved in the attachment of the signals proteins give to each other.Although subsequent analysis showed that the interaction between SCE and Rep probably occurs via SUMO1.
The next question the researchers had was if Rep binds SUMO1 in a similar way as plants proteins bind SUMO1, via a SIM motif. To analyse this the researchers adapted SUMO1 in such a way that it can no longer bind a SIM motif. As a consequence, it turned out, SUMO1 could no longer bind Rep.
Subsequently the researchers searched in the Rep protein for the SIM motif. They found this motif laying nearby the ATPase domain of the protein. To confirm that this SIM motif is indeed needed for binding SUMO1, the researchers mutated three core amino acids of this motif. Changing one of those three amino acids did not interfere with the binding to SUMO1 but changing two or three amino acids prevented the binding between Rep and SUMO1.
Reduced virus reproduction
This, they found after testing, also had consequences for the rate of virus reproduction. Viruses in which all three SIM amino acids were mutated in Rep hardly multiplied at all.
Because the SIM motif is nearby the ATPase domain of the protein, the researchers wondered if changes in the SIM motif also affected the ATPase activity of Rep. After testing, it turned out that this was indeed the case, Rep with a mutated SIM motif had lower activity than Rep without a mutated SIM motif.
The question that remains is whether the reduced reproduction of the virus is due to the absence of the interaction between Rep and SUMO1, or because the changes in SIM also reduced the ATPase activity. An answer on this question is needed when researched want to decide if it is worthwhile to introduce changes in SUMO1 to make plants resistant to the tomato yellow leaf curl virus and related viruses.
Literature
Gaertner NF, Maio F, Arroyo-Mateos M, Luna AP, Sabarit B, Kwaaitaal M, Eltschkner S, Prins M, Bejarano ER, van den Burg HA. 2025, A SUMO interacting motif in the replication initiator protein of tomato yellow leaf curl virus is required for viral replication. J Virol 0:e01286-25. https://doi.org/10.1128/jvi.01286-25