LAUSR

Infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry imaging is a useful tool for identifying important meta-metabolomic features pertinent for enhancing our understanding of biological systems. Magnaporthe oryzae (M. oryzae) is a filamentous fungus that is the primary cause of rice blast disease. True to its name, M. oryzae primarily destroys rice crops and can also destroy other cereal crops as well. In a previous study, the F-box E3 ligase protein in M. oryzae was noted to be crucial for its growth and pathogenicity. In this study, we inoculated three separate sets of barley with wild-type M. oryzae, an F-box E3 ligase protein knock out of M. oryzae, and a control solution. Over the course of the infection (8 days), we imaged each treatment after development of an advanced polarity switching method, which allowed for the detection of low and high molecular weight compounds that ionize in positive or negative polarities. A set of features from initial experiments were chosen for another analysis using tandem mass spectrometry. Serotonin, a barley defense metabolite, was a compound identified in both positive and negative modes. Serotonin was putatively identified using MS1 data including carbon estimation and sulfur counting then confirmed based on tandem mass spectrometry fragmentation patterns. Metabolites in the melanin pathway, important for infection development of M. oryzae, were also identified using MS1 data but were unable to be confirmed with MS/MS due to their low abundances.