Analysis of the molecular mechanisms of plant defense against microbial pathogens

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Sensing and defending against microbial infection is essential to the survival of multicellular organisms. Plants mainly use two types of immune receptors to recognize pathogens and activate downstream defense responses. Transmembrane receptors are used to recognize conserved features of microbes such as bacterial flagellin, whereas intracellular receptors with nucleotide binding and leucine-rich repeats domains (NLRs) are used to detect specific proteins from pathogens that are secreted into the plant cell to promote colonization. The proposed research aims to understand how immunity mediated by these two types of immune receptors is regulated at molecular level.*** *** Activation of plant immunity leads to rapid transcriptional reprogramming. Our previous studies identified SAR Deficient 1 (SARD1) as a master transcription factor which regulates the expression of a large number of key immune regulators. The expression of SARD1 is strongly induced by pathogen infection and increase in SARD1 expression is sufficient to activate plant defense against pathogens. One big question we are going to address is how defense signals are transduced from plasma membrane-localized immune receptors to activate the expression of SARD1 in the nucleus. We are going to use a combination of molecular genetic, genomic and biochemical approaches to identify and characterize regulatory components involved in the this process. Another question related to immunity mediated by transmembrane immune receptors which we are going to address is how heterotrimeric G proteins regulate the protein level of a critical signaling component downstream of the receptors. ****** Since the first report of NLR receptors in Arabidopsis about two decades ago, many plant NLR proteins have been identified and tremendous progress has been made on how they recognize pathogens. However, there is still very little known about how NLR receptors activate downstream defense responses. Our previous studies identified several proteins that are involved in immunity mediated by the NLR receptor SUMM2. We are going to test whether they function downstream of SUMM2 to transduce defense signals and determine how they regulate plant immunity. This investigation may lend insights on how defense signals are transduced from NLR receptors to activate plant defense.****** Our research is crucial for advancing our knowledge of how plant immunity is regulated. New regulators and signaling mechanisms involved in plant defense responses will be discovered. The knowledge obtained will contribute to the development of better strategies to control plant diseases through environmentally friendly means. **