Role of kinases and an epigenetically regulated gene in soybean cyst nematode resistance

Soybean cyst nematode (SCN) is the most devastating and economically important pathogen of soybean across the United States and globally. The current primary control for SCN is with the use of resistant cultivars, however, SCN populations are shifting to overcome most common sources of soybean resistance. This research was conducted to identify novel sources of genetic resistance to SCN. First, I functionally characterized two protein kinase hub genes whose function are predicted to be essential for mediating soybean susceptibility to SCN. I generated kinase-dead variants by mutating two amino acids required for the kinase enzymatic activity. Overexpression of the kinase-dead variants resulted in significant decreases in plant susceptibility to SCN. Furthermore, transcriptome analysis revealed that both protein kinases act as negative regulators of various defense and immunity pathways. Through quantitative phosphoproteomic analysis, I found that one of these two kinases, BAK1-INTERACTING RECEPTOR LIKE KINASE1 (BIR1), contributes to plant susceptibility by modulating alternative splicing events upon SCN infection. The second protein kinase, mitogen-activated protein kinase kinase 2 (MKK2), was found to negatively regulate plant defense and immunity signaling pathways during SCN infection by regulating transcription and translation initiation factors. I also functionally characterized an epigenetically regulated gene encoding a SNARE-associated vacuole membrane protein (GmVMP1). Overexpression of GmVMP1 resulted in complete resistance to SCN in susceptible soybean cultivars, establishing GmVMP1 as a major SCN resistance gene. Further experimental assays revealed that GmVMP1 interacts with proteins involved in diverse biological processes, including autophagy, vesicle trafficking, cell wall biosynthesis, and defense signaling, a finding that may explain the robust function of GmVMP1 in suppressing SCN parasitism of soybean. These newly identified sources of SCN resistance in this dissertation are expected to provide effective and durable avenues for generating SCN-resistant soybean cultivars.