Plant diseases are a major source of agricultural yield loss every year, despite use of current and somewhat successful disease control methods. An understanding of the molecular mechanisms that plants use to respond to pathogen infections can contribute to our long-term ability to more successfully manage plant diseases (for example by improved plant breeding, or by chemical or biotechnology approaches that stimulate better disease resistance). The investigators have discovered that poly(ADP-ribosyl)ation processes are active in infected plants and that manipulation of these processes alters the plant defense response. In the present project, molecular genetics and biochemistry/cell biology approaches will be used to investigate two main Specific Aims: 1) Determine how pathogen-elicited plant cell wall reinforcement is impacted by poly(ADP-ribosyl)ation, and 2) Dissect additional roles of poly(ADP-ribosyl)ation in defense-associated DNA repair and in apoptosis, using recent findings to discover new genes and pathways with functional roles in plant immunity. Broader Impacts of this study will arise foremost through better understanding of this previously undiscovered component of plant immunity. Accommodation of DNA damage and related stresses, a main role of poly(ADP-ribosyl)ation in other organisms, is highly relevant in an era of ozone depletion and climate change, where there can be synergy between stress caused by pathogens and stress caused by the abiotic environment. In addition, plant cell wall biology is a subject of high interest due to its relevance to biofuels (cell wall reinforcement in response to pathogens is altered when poly(ADP-ribosyl)ation is altered). Broader impacts of the project will also arise through education/outreach activities that engage college and high school students in research, including under-represented minorities, and that train graduate students and postdocs in effective mentoring of younger students to create research experiences that get students engaged and excited about science.
Organisms must maintain the integrity of their DNA as they experience environmental stresses caused by pathogen infections or non-biological hardships such as drought or exposure to intense light. Plants do not handle these stresses in the same way as animals. During the current NSF-funded project our research group made the major discovery that microbial plant pathogens impose significant DNA damage on host plant cells, which must be mitigated. Poly(ADP-ribosyl)ation plays significant roles in repair of DNA damage in animals, and our research group had already identified poly(ADP-ribosyl)ation as an important contributor to successful plant defense responses, hence the above discoveries are logically connected. We also discovered that the plant enzyme PARP2 makes the greatest contribution to poly(ADP-ribose) polymerase activity and organismal viability in response to DNA damaging stresses, and that PARP2 also makes stronger contributions than PARP1 to plant immune responses. This revealed that core aspects of plant poly(ADP-ribosyl)ation are mediated by substantially different enzymes than in animals, suggesting substantial differences in regulation of plant poly(ADP-ribosyl)ation and DNA repair. Our research group had also previously discovered that pathogen-elicited callose deposition (a plant cell wall reinforcement process that is a core component of plant immune responses) is impacted by inhibitors of poly(ADP-ribosyl)ation. During the present project we made further progress in understanding the specific cellular/physiological stage at which this altered cell wall reinforcement is regulated. This study therefore revealed basic mechanisms by which plants - crucial organisms for human food, fiber, oxygen, carbon capture and numerous other ecosystem services - respond effectively to environmental stresses. In addition to the above scientific contributions, the project provided broader societal impacts by attracting to scientific research, and training, multiple undergraduate student researchers, including students from primarily undergraduate institutiions. We also further developed the scientific mentoring skills of four Ph.D.-level scientists to raise their effectiveness in attracting and retaining future generations of scientists.
