Bacterial Toxin Hijacks Plant Hormone Signaling

Bacterial Toxin Mimics Plant Hormone to Hijack Signaling Pathway

This study investigates how a bacterial toxin called

can mimic a plant hormone called

jasmonoyl isoleucine (JA-Ile)

Jasmonoyl isoleucine (JA-Ile) is a plant hormone that plays an important role in the plant's defense against diseases and other stresses.

 

to manipulate the plant's defense mechanisms and promote disease.

Coronatine Targets the JA-Ile Signaling Pathway

The researchers found that

, a virulence factor produced by the bacterial pathogen

Pseudomonas syringae

Pseudomonas syringae is a type of bacteria that can infect and cause disease in plants.

 

, can bind to and activate the same plant proteins that normally respond to the hormone JA-Ile. Specifically, coronatine interacts with the

F-box protein COI1

COI1 is a protein in plants that acts as a receptor for the plant hormone JA-Ile and the bacterial compound coronatine. When COI1 binds to these molecules, it can interact with other proteins to activate the plant's defense response.

 

and causes it to bind to

JAZ repressor proteins

JAZ proteins are a group of proteins in plants that normally act to repress or block the plant's defense response. When JA-Ile or coronatine binds to COI1, it can cause the JAZ proteins to be degraded, allowing the defense response to be activated.

 

in the plant

Arabidopsis

Arabidopsis is a small flowering plant that is commonly used as a model organism in plant biology research.

 

.

The Jas Motif is Critical for COI1-JAZ Interactions

The researchers determined that the critical region for this interaction is the

at the C-terminus of the JAZ proteins, rather than the

N-terminal

The N-terminal refers to the end of a protein that has the amino acid nitrogen (N) group.

 

or

ZIM domain

The ZIM domain is a region within the JAZ proteins that is involved in their ability to repress the plant's defense response.

 

. They found that two specific positively charged amino acid residues (R205 and R206) within the Jas domain of the JAZ1 protein, and the corresponding residues (R223 and K224) in JAZ9, are essential for the coronatine-mediated COI1-JAZ interaction.

Disrupting the COI1-JAZ Interaction Enhances Plant Resistance

Interestingly, plants expressing mutant JAZ1 proteins with changes to these critical basic residues exhibited JA-insensitive phenotypes, including enhanced resistance to infection by P. syringae. This suggests that the bacterial toxin coronatine targets the physical interaction between COI1 and the Jas domain of JAZ repressors as a mechanism to hijack the plant's jasmonate signaling pathway and promote disease.

Jasmonate Signaling Pathway Regulation

In the absence of JA-Ile or coronatine, the C-terminus of JAZ proteins binds to and represses transcription factors like

. However, the binding of JA-Ile or coronatine to COI1 triggers the degradation of JAZ proteins, allowing the transcription factors to activate JA-responsive genes and initiate the plant's defense response.

Conclusion

This study provides important insights into the molecular mechanisms underlying jasmonate signaling in plants. The researchers have identified a critical role for the Jas motif in the COI1-JAZ interaction, and have shown how the bacterial toxin coronatine can exploit this interaction to manipulate the plant's defense system. Understanding these mechanisms can help develop strategies to improve plant resistance against pathogens.