CAREER:Exploring apoplastic sulfate restriction and stress response mis-regulation as major mechanisms of pattern-triggered immune action on bacteria

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Plants are constantly challenged by invading microbes. To counter these invaders, plants deploy a robust and effective immune system capable of detecting, appropriately responding to and restricting the proliferation of most microbes. While the molecular mechanisms underlying the detection of microbes and the signaling mechanisms associated with the induction of immunity are understood in ever increasing detail, the molecular mechanism(s) by which microbial proliferation is restricted by immune functions have been elusive. The long-term goal of this project is to understand the bacterial mechanisms targeted by plant immune action. Immune-activated plants appear to limit available sulfur, an essential element for life, thus blocking bacterial proliferation. Plant immunity also interferes with conserved bacterial responses to stress, resulting in the increased sensitization of bacteria to immune outputs. Characterizing these potential modes of immune action will have broad implications for our understanding of plant immunity and provide new targets and practical strategies to manage plant diseases. The project's broad educational goals include increasing pre-graduate competency in plant pathology, teaching plant and plant disease science to students from all backgrounds, including non-science majors, and enhancing scientific understanding through inquiry-based learning. The project's broader impacts expand public knowledge of plant diseases and may suggest new crop protection solutions. Driven by host recognition of conserved microbe-associated molecular patterns, Pattern Triggered Immunity (PTI) is the first line of induced immune defenses used by plants against invading pathogens. PTI plays a key role in restricting the unchecked growth of microbes. However, the mechanisms by which PTI restricts the growth of broad classes of microbes are unclear. The transcriptional response of bacterial pathogens to PTI is the basis for this project's focus on mechanisms of PTI action that restrict pathogen growth. Deploying plant genetics, forward and reverse bacterial genetics, chemical and protein analysis, and bacterial transcriptomics, this CAREER project will test the following hypotheses: 1) Apoplastic sulfate sequestration restricts bacterial proliferation during PTI; 2) PTI outputs interfere with activation of the AlgU bacterial stress response cascade, resulting in increased bacterial sensitization to immune-associated stressors; and 3) although PTI outputs are multifaceted and semi-redundant, bacterial responses to PTI can be used to delineate and link specific outputs to sectors of the plant defense network. This project incorporates educational activities aimed at raising public knowledge about plant diseases and immunity and will focus on the education of non-specialist students. These goals will be achieved by the development of two undergraduate inquiry-based learning courses incorporating plant disease agricultural biotechnology concepts and targeted towards non-science majors, and by piloting peer-mentored, inquiry-based learning lesson plans about plant-microbe interactions for teachers in Athens-Clarke County, Georgia, middle schools.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.