Ecological systems can have alternative stable states, in which transitions between these states are triggered by impulsive disturbances (e.g., annual harvesting), environmental degradation (e.g., continual loss of habitat), or both. These stable states may be desirable (e.g., higher densities of a threatened species) or undesirable (e.g., extinction or low densities). This project aims to understand the resilience of bistable systems to environmental degradation and impulse disturbances. To this end, we constructed an ordinary differential metapopulation model with alternative stable states to analyze the dynamics of these systems. Firstly, we analyzed the model without disturbances to understand its baseline dynamics. Next, we introduced an environmental degradation parameter, which linearly decreases the proportion of habitable land. With this introduced, we identified a rate-dependent region in the state space for which rate-induced tipping could occur. These results suggest that though rate-induced tipping is possible, it is limited to a small region of the state space. For ecological systems, this illustrates the window in which the rate of environmental degradation affects long-term survivability. Secondly, with the base model, we utilized a flow-kick framework with the metapopulation model and a constant kick size to model impulse disturbances applied over fixed time intervals. With the flow-kick framework, we described the disturbance regimes in which the system can persist and those that are too extreme for persistence. For ecological systems, this provides a basis to understand the behavior of a system undergoing periodic impulse disturbances, such as its ability to survive or go extinct.

Common rust of corn (Zea mays), caused by the biotrophic fungus Puccinia sorghi, is an economically significant foliar disease that challenges production across major growing regions. Despite the agricultural importance of common rust, the molecular mechanisms underlying its pathogenicity remain largely unknown. Plant active immunity relies heavily on intracellular defense responses, which rust fungi suppress or manipulate through secreted effector proteins. Building on previous work that isolated candidate P. sorghi effectors, this study aims to systematically characterize approximately 20 of these proteins to elucidate their specific roles in virulence. Candidate effectors are being molecularly cloned into expression vectors utilizing the GreenGate system. To determine their spatial distribution within host cells, Agrobacterium tumefaciens-mediated transient expression was performed in the model plant Nicotiana benthamiana. Subcellular localization was visualized using a BioRad ZOE cell imager and confocal microscopy to identify effectors targeting key compartments, such as the nucleus, where they may modulate host transcription or defense signaling. To validate protein expression and assess virulence functions in the native host, downstream steps include Western blot verification and disease-assessment assays using heterologous expression in maize. Characterizing these spatial and functional dynamics will provide critical insights into how rust effectors manipulate host machinery, ultimately aiding the identification and engineering of robust resistance targets in corn.

The purpose of this study is to understand the interactions between the gap genes kruppel (kr) and hunchback (hb) during embryological development in non-model insects, specifically in the western corn rootworm, Diabrotica virgifera virgifera Le Conte. Gap genes are a class of genes involved in the development of segmentation of the body in the embryological development of insects. These genes and their interactions are well understood in model organisms such as Drosophila melanogaster and Tribolium castaneum but are poorly characterized in non-model species. Hb and kr are essential transcription factors for specifying the anterior/posterior body axis in insects. The interactions between these gap genes were studied through RNA interference (RNAi). RNAi is a post-transcriptional gene silencing mechanism widely used to study gene function In this study, hb specific double-stranded RNA was fed to adult western corn rootworms and females were allowed to lay eggs to evaluate for larval phenotype. The eggs were flash-frozen, collected, and analyzed using quantitative real-time PCR to measure the expression of hb and kr. The data was analyzed with RStudio using a one-way analysis of variance, and the means of the treatments were compared using Student’s t-test with Dunnett’s adjustment. Based on prior research, we expect that the silencing of hb will cause the embryos to fail to develop proper thoracic and anterior segments in the abdominal region and will affect the expression of kr.

Phenylpropanoids are secondary metabolites produced by plants that are important for both plant and human sustenance. Phenylalanine ammonia lyase (PAL) catalyzes the entry step of the phenylpropanoid pathway by converting phenylalanine to trans-cinnamic acid. PAL interacts with the next enzyme in the pathway, cinnamate-4-hydroxylase (C4H), which converts trans-cinnamic acid to p-coumaric acid. Phenylalanine/tyrosine ammonia lyase (PTAL) enzymes are found in grasses. They can convert tyrosine to p-coumaric acid in one step, while retaining the ability to convert phenylalanine to trans-cinnamic acid. While this “metabolically flexible” PTAL has been shown to function in the Nicotiana benthamiana transient expression system, the effects of this enzyme when stably expressed in Arabidopsis thaliana are unknown. This study will create stable transgenic Arabidopsis plants expressing PTAL and analyze the effects on the phenotype and metabolite profile. Although Arabidopsis typically does not accumulate high levels of tyrosine, we will express deregulated tyrosine together with PTAL in our plants. I hypothesize that expressing this enzyme in Arabidopsis in a background high in tyrosine will allow us to increase and direct phenylpropanoid production in these plants. Studying PTAL function in Arabidopsis will help us take one step toward increasing overall phenylpropanoid production in plants.