Plant cell under attack, activated Rx1 receptors with damaged DNA.

Unlocking Immunity: How Activation of Immune Receptor Rx1 Reveals the Secrets to Cell Death

Lena Voss in Science & Nature July 2025 • 4 min read.

"Discover the groundbreaking research on immune receptor Rx1 and its critical role in triggering distinct immune responses that lead to cell death, potentially revolutionizing plant immunity and disease resistance strategies."

In the ongoing battle between plants and pathogens, the immune system plays a pivotal role. Plants, like humans, have evolved sophisticated defense mechanisms to recognize and neutralize threats. Central to this defense are intracellular NLR (nucleotide-binding leucine-rich repeat) immune receptors, which act as sentinels, detecting pathogen invasions and triggering protective responses.

Understanding how these immune receptors function is crucial for developing strategies to enhance plant immunity and protect crops from devastating diseases. However, studying these receptors is challenging. The activation of immune responses is often non-uniform and asynchronous, making it difficult to dissect the precise sequence of events and their cellular effects.

To overcome these challenges, researchers have developed innovative systems to synchronize and control immune receptor activation. One such system, called CESSNA (Controlled Expression of effectors for Synchronized and Systemic NLR Activation), allows scientists to study immune responses in a more controlled and systematic manner.

Rx1: A Deep Dive into Immune Activation

Plant cell under attack, activated Rx1 receptors with damaged DNA.

A recent study delved into the activation of the Rx1 immune receptor in potatoes using the CESSNA platform. Rx1 is known for its role in providing extreme resistance to Potato Virus X (PVX). The study aimed to unravel the precise sequence of events that occur following Rx1 activation, leading to a deeper understanding of its function and the broader implications for plant immunity.

The researchers found that Rx1 activation triggers a cascade of distinct immune responses, each occurring at specific time points. This precise timing is crucial for orchestrating an effective defense response. Here's a breakdown of the key events:

ROS Burst and Ion Leakage (Within 1 Hour): Rx1 activation triggers a rapid burst of Reactive Oxygen Species (ROS) and ion leakage, indicating an early response to the perceived threat.
Autofluorescence Change and HIN1 Expression (2 Hours): Changes in autofluorescence and increased expression of the HIN1 gene, a marker for cell death, signal the progression of the immune response.
DNA Damage (2-3 Hours): Single-strand DNA damage becomes apparent, followed by double-strand DNA damage, indicating cellular stress and the activation of DNA repair mechanisms.
Defense Gene Expression and Cell Death (4 Hours): Increased expression of defense-related genes, such as PR-1a, LOX, ERF1, and AOX1B, culminates in cell death, effectively containing the infection.

Interestingly, the study also explored the impact of Rx1 localization within the cell. They found that nuclear exclusion of Rx1 led to increased basal levels of ROS and permitted Rx1 activation by a Rx1-breaking CP variant. In contrast, nuclear-targeted Rx1 showed diminished basal ROS levels, and only wildtype CP could trigger a compromised ROS production. This highlights the importance of Rx1's dynamic distribution between the cytosol and nucleus for its proper function.

The Future of Plant Immunity

This research provides valuable insights into the intricate mechanisms of Rx1 activation and its role in triggering immune responses leading to cell death. By understanding the precise timing and location of these events, scientists can develop more effective strategies to enhance plant immunity and protect crops from disease. The CESSNA system offers a powerful tool for dissecting the complexities of plant immunity, paving the way for future discoveries and innovative solutions.

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Everything You Need To Know

What cascade of events does the activation of the immune receptor Rx1 trigger in plant cells?

The activation of the immune receptor Rx1 triggers a cascade of events. Initially, there's a rapid burst of Reactive Oxygen Species (ROS) and ion leakage within an hour. Around two hours, changes in autofluorescence occur alongside increased expression of the HIN1 gene, which is a marker for cell death. By 2-3 hours, single-strand, and then double-strand DNA damage become apparent. Finally, at about four hours, there's increased expression of defense-related genes like PR-1a, LOX, ERF1, and AOX1B, culminating in cell death to contain the infection.

What is the purpose of the CESSNA system in studying plant immunity?

The CESSNA (Controlled Expression of effectors for Synchronized and Systemic NLR Activation) system enables researchers to synchronize and control immune receptor activation in plants. This is crucial because it allows scientists to study immune responses, like those triggered by Rx1, in a more controlled and systematic way, making it easier to dissect the precise sequence of events and their cellular effects. It helps overcome the challenges posed by the often non-uniform and asynchronous nature of immune responses in plants.

What are NLR immune receptors, and why are they important for plant defense?

NLR (nucleotide-binding leucine-rich repeat) immune receptors, like Rx1, function as intracellular sentinels within plant cells. They recognize pathogen invasions and trigger protective responses. They are essential components of a plant's defense mechanism, similar to the immune system in humans. By understanding how these receptors function, scientists can develop strategies to enhance plant immunity and protect crops from devastating diseases. However, NLRs are only one component of plant immunity, future research is needed to understand how they work with other immune components.

How does the location of the Rx1 immune receptor within the cell affect its function and activation?

The study revealed that the localization of the Rx1 immune receptor within the cell impacts its function. When Rx1 was excluded from the nucleus, basal levels of Reactive Oxygen Species (ROS) increased, and Rx1 could be activated by a Rx1-breaking CP variant. Conversely, when Rx1 was targeted to the nucleus, basal ROS levels decreased, and only wildtype CP could trigger a compromised ROS production. This dynamic distribution between the cytosol and nucleus is important for Rx1 to function correctly.

What are the broader implications of understanding the Rx1 activation mechanism for improving plant immunity and disease resistance?

Understanding the activation mechanism of the Rx1 immune receptor and the downstream defense responses, including the burst of Reactive Oxygen Species (ROS), activation of HIN1, DNA damage, and expression of defense genes like PR-1a, LOX, ERF1, and AOX1B, leading to cell death, provides a foundation for developing strategies to enhance plant immunity. This knowledge may enable scientists to manipulate these pathways to create plants with enhanced disease resistance. Furthermore, the CESSNA system offers a valuable tool for future research in this field.