New Research Uncovers How Plant Cells Defend Against Pathogens

In the realm of biology, the defense mechanisms of living organisms against threats are a subject of great interest. While the human body deploys a diverse array of immune cells that circulate throughout the body, safeguarding against everything from minor cuts to complex diseases like cancer, plants face a different set of challenges. Plant cells are immobile, compelling each individual cell to handle its own immunity while simultaneously fulfilling other crucial functions such as photosynthesis and growth. Until recently, the exact processes by which these multitasking plant cells detect threats, communicate them, and mount an effective response remained a mystery.

Scientists at the Salk Institute have now made a significant breakthrough. Their research, published in Nature on January 8, 2025, reveals how plant cells adapt to protect themselves from pathogens. When a threat is detected, plant cells enter a specialized immune state and transform into PRimary IMmunE Responder (PRIMER) cells. These PRIMER cells are a newly identified cell population that serves as a central point to initiate the immune response.

The researchers also found that PRIMER cells are surrounded by another group of cells, which they named bystander cells. These bystander cells seem to play a vital role in transmitting the immune response throughout the entire plant.

Professor Joseph Ecker, the senior author of the study, Salk International Council Chair in Genetics, and Howard Hughes Medical Institute investigator, emphasizes the importance of a well - functioning immune system in plants. In nature, plants are constantly under attack from various pathogens, yet they lack mobile, specialized immune cells like humans. Instead, they have developed a unique system where every cell can respond to immune threats without neglecting its other functions. However, until this study, the exact mechanism of how plants achieved this balance was unclear.

Plants encounter a wide variety of pathogens. Bacteria can infiltrate through the pores on the leaf surface, while fungi may directly invade plant "skin" cells. Given that plant cells are stationary, each cell becomes solely responsible for responding to pathogens and alerting nearby cells when an attack occurs. Moreover, different pathogens can enter a plant at different times and locations, resulting in various immune response stages happening simultaneously across the plant.

To unravel the complex immune response of plants, the Salk team utilized two sophisticated cell profiling techniques: time - resolved single - cell multiomics and spatial transcriptomics. By combining these two methods, the researchers were able to capture the plant immune response in each cell with an unprecedented level of spatiotemporal resolution.

The research team introduced bacterial pathogens to the leaves of Arabidopsis thaliana, a commonly used model plant in research. After analyzing the plant's response, they comprehensively identified the state of each cell upon infection. This analysis led to the discovery of a novel immune response state, the PRIMER cells, which emerged at specific immune hotspots within the plant. These PRIMER cells expressed a new transcription factor called GT - 3a. This protein likely acts as an important upstream signal, alerting other cells to the presence of an active immune response.

Equally significant were the bystander cells surrounding the PRIMER cells. These neighboring cells were found to express genes that enable long - distance cell - to - cell communication. Although the researchers plan to further explore this relationship in future studies, they currently suspect that the interactions between PRIMER and bystander cells are essential for spreading the immune response across the leaf.

The new spatiotemporal, cell - specific insights into the plant immune response have been compiled into a reference database that is now publicly available to researchers worldwide. In a world where pathogens are evolving and spreading due to climate - related environmental changes and increasing antibiotic resistance, this database provides a crucial starting point for ensuring the health of plants and crops.

Ecker expresses excitement about creating a publicly available cell atlas, given the current high demand for such detailed resources. He believes that this atlas could lead to numerous new discoveries about how individual plant cells respond to environmental stressors, which is essential for developing more climate - resilient crops.

The research was a collaborative effort. Other authors include Joseph Nery of Salk; Alexander Monell of Salk and UC San Diego; Travis Lee of Salk and Howard Hughes Medical Institute; Yuka Sakata, Shoma Shirahama, and Akira Mine of the University of Kyoto in Japan. The work was supported by the Howard Hughes Medical Institute and the Human Frontiers Science Program.