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Deciphering the guard cell metabolome in plant pathogen defense


Crops are constantly challenged by bacterial pathogens, which cause huge losses in yield and economical value every year. The pathogens enter the plant body through wounds and through tiny pores on leaf surfaces. These pores are called stomata, and are formed by highly specialized cells called guard cells. Stomatal opening mediated by the guard cells allows carbon dioxide uptake. After uptake, carbon dioxide is captured by photosynthesis, generating organic materials such as carbohydrates; therefore stomatal opening is critical for agricultural yield and bioenergy production. However, the open stomatal pores also allow water vapor loss, and create entries for pathogens, which are liabilities for plants. It is known that when guard cells sense pathogens, they close stomata within an hour as an immune response. However, subsequently, the stomata open again and pathogens go in. This project aims to elucidate how lipids and fatty acids function in regulating the stomatal closure and opening during pathogen infection. This research will enable scientists to gain an in-depth understanding of guard cell lipid metabolites important for pathogen triggered stomatal closing and opening. The outcome of the research has broad societal impact, e.g., for informing rational crop breeding to enhance pathogen defense and crop yield. The results will be made available to the public via community repositories and no-cost publications (e.g. Metabolight, the Plant Journal). The project will also enable cross-disciplinary training of students at different levels, including women and under-represented students. Training the next generation of scientists and citizens has far-reaching positive impacts for society and the world.<br/><br/>The Chen lab has observed significant lipid metabolite changes in guard cells in response to treatment with a bacterial elicitor comprised of the flagellin N-terminal 22 amino acid peptide (flg22). The Assmann lab has previously demonstrated the effect of the lipid metabolite sphingosine-1-phosphate (S1P) as a component of abscisic acid signaling. However, the roles of S1P and other lipids and fatty acids in stomatal immunity against Pseudomonas syringe pv. tomatao (Pst DC3000) are not known. Here the hypothesis is that lipid metabolites function as important regulators of guard cell pathogen signaling. The goals are to: 1) determine dynamic changes of lipids and fatty acids in guard cells during Pst DC3000 triggered stomatal movement; 2) determine stomatal movement triggered by Pst DC3000 in relevant mutants of lipid biosynthesis and metabolism implicated from the lipidomics analyses, and characterize the effects of lipid metabolites as signaling molecules in triggering stomatal movement. Approaches to be used include lipidomics, cell biology, genetics and biochemistry. This focused project specially targets the functions of lipids and fatty acids in stomatal immunity against Pst DC3000. The results are expected to reveal novel lipid metabolite functions, boost understanding of molecular mechanisms that underlie stomatal immunity, and illustrate the power of integrated approaches involving lipidomics to reveal novel biological mechanisms<br/><br/>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.

Sixue Chen; Sarah Assmann
University of Florida
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