Dr. Greg Martin is studying the interactions between plants and pathogens during attempted infections to gain insight into the plant immune system. Using a two-pronged approach--one focused on the plant's immune responses to invaders and the other centered on the ways a pathogen undermines those responses--he is uncovering both general and specific principles that have implications for plant and human health. From the plant perspective, understanding the details of pathogen infections will lead to the mitigation of crop damage without needing as many pesticides or other disease control methods. Instead, the natural genetic variation of plants can be used to develop plants that are inherently more resistant to diseases. Because the plant's initial immune response is similar in nature to human innate immunity, knowledge of the general aspects of pathogen attack, specifically bacterial infection, can also be applied to studies of the human immune system, potentially leading to better treatments to combat infection.

Dr. Greg Martin, Boyce Schulze Downey Professor at the Boyce Thompson Institute for Plant Research and Professor of Plant Pathology and Plant-Microbe Biology at Cornell University, is studying the interactions between pathogens and the plant immune system to uncover information about how pathogens infect plants. Studying the plant-pathogen system, specifically the genes and proteins involved, leads to new knowledge about how bacteria cause diseases in plants. These observations often apply to pathogens infecting both plants and humans and therefore have implications for the development of strategies that will be useful in targeting pathogens in both agricultural and medical settings. At the same time, Dr. Martin is learning principles about the plant immune system that in some cases are also relevant to understanding the human immune system. Plants have many experimental advantages compared to humans, and performing experiments with them leads to discoveries that might be difficult or impossible to learn using other systems.

In the coming year, Dr. Martin's lab will focus on four areas of research related to bacterial pathogens and the plant immune system:

1. When a pathogen is in the presence of a plant, the plant has the interesting ability to use extracellular protein receptors to detect the microbe by identifying highly conserved molecules, e.g., flagellum, cell wall fragments, specific proteins, that the pathogen generally needs for its lifestyle. These host receptors are partly outside and partly inside the cell, and upon detecting a threat they transmit a signal, which in turn triggers an immune response within the plant cell. In fact, humans share this stage of the immune system response in our innate immunity. This is similar to a guard posted at a turret in a castle, who signals a warning in the face of an invasion threat. In response to this warning, the warriors prepare for battle representing the plant's triggered initial immune response. Dr. Martin is working to identify which protein receptors plants have, and which components of the pathogen threat are being recognized.

2. Despite the plant activating an immune response, many pathogens have devised methods to undermine that initial plant immune response. In order to infect the plant, the pathogen must interfere with the immune response. They do so by using a "syringe-like" device to poke through the plant cell wall and inject virulence proteins, so called because they promote pathogen virulence, into the plant cells, that focus on specific host "targets." This subversion of the plant's defenses can be likened to using a Trojan horse to sneak an invading army through the gates of an armed defense. Dr. Martin is identifying the ways a pathogen infects the plant by identifying which proteins are being injected and how they are interfering with the host cell's natural biological functions.

3. In a step unique to the plant immune system, plants have discovered a method of launching a second, super-strong immune response by detecting specific virulence proteins. Although some 30 or so virulence proteins may be injected, the plant cell only needs to identify one to activate this secondary response, which has the potential to completely shut down the pathogen infection. Following the castle analogy, the host (plant) is now focusing its defenses on the invading army (pathogen virulence proteins) that are flooding out of the Trojan horse. Dr. Martin is working to discover which of the virulence proteins are triggering the plant's second immune response, what are the host proteins that are associated with the second immune response, and how do they combat the pathogen threat.

4. At this stage, it appears as though the plant's defenses have won and have successfully pacified the bacterial attack. Common sense though will tell us by looking at an infected plant that this is not the end of the plant-pathogen battle. As it turns out, some pathogens have evolved further and now possess the ability to undermine even this second super-strong immune response. Though relatively rare, there are a few pathogen proteins that can do this. This back-and-forth battle is comparable to the invading army retreating with a few straggling soldiers, only to rebuild, preparing for another future fight. At this stage, Dr. Martin is identifying which pathogen proteins can undermine the plant's second immune response, and how are they able to further evolve to combat the second response.