Changing course: Glucose starvation drives nuclear accumulation of Hexokinase 2 in S. cerevisiae.

Glucose is the preferred carbon source for most eukaryotes, and the first step in its metabolism is phosphorylation to glucose-6-phosphate. This reaction is catalyzed by hexokinases or glucokinases. The yeast Saccharomyces cerevisiae encodes three such enzymes, Hxk1, Hxk2, and Glk1. In yeast and mammals, some isoforms of this enzyme are found in the nucleus, suggesting a possible moonlighting function beyond glucose phosphorylation. In contrast to mammalian hexokinases, yeast Hxk2 has been proposed to shuttle into the nucleus in glucose-replete conditions, where it reportedly moonlights as part of a glucose-repressive transcriptional complex. To achieve its role in glucose repression, Hxk2 reportedly binds the Mig1 transcriptional repressor, is dephosphorylated at serine 15 and requires an N-terminal nuclear localization sequence (NLS). We used high-resolution, quantitative, fluorescent microscopy of live cells to determine the conditions, residues, and regulatory proteins required for Hxk2 nuclear localization. Countering previous yeast studies, we find that Hxk2 is largely excluded from the nucleus under glucose-replete conditions but is retained in the nucleus under glucose-limiting conditions. We find that the Hxk2 N-terminus does not contain an NLS but instead is necessary for nuclear exclusion and regulating multimerization. Amino acid substitutions of the phosphorylated residue, serine 15, disrupt Hxk2 dimerization but have no effect on its glucose-regulated nuclear localization. Alanine substation at nearby lysine 13 affects dimerization and maintenance of nuclear exclusion in glucose-replete conditions. Modeling and simulation provide insight into the molecular mechanisms of this regulation. In contrast to earlier studies, we find that the transcriptional repressor Mig1 and the protein kinase Snf1 have little effect on Hxk2 localization. Instead, the protein kinase Tda1 regulates Hxk2 localization. RNAseq analyses of the yeast transcriptome dispels the idea that Hxk2 moonlights as a transcriptional regulator of glucose repression, demonstrating that Hxk2 has a negligible role in transcriptional regulation in both glucose-replete and limiting conditions. Our studies define a new model of cis- and trans-acting regulators of Hxk2 dimerization and nuclear localization. Based on our data, the nuclear translocation of Hxk2 in yeast occurs in glucose starvation conditions, which aligns well with the nuclear regulation of mammalian orthologs. Our results lay the foundation for future studies of Hxk2 nuclear activity.

Optimization of the fluorogen-activating protein tag for quantitative protein trafficking and colocalization studies in S. cerevisiae.

Spatial and temporal tracking of fluorescent proteins (FPs) in live cells permits visualization of proteome remodeling in response to extracellular cues. Historically, protein dynamics during trafficking have been visualized using constitutively active FPs fused to proteins of interest. While powerful, such FPs label all cellular pools of a protein, potentially masking the dynamics of select subpopulations. To help study protein subpopulations, bioconjugate tags, including the fluorogen activation proteins (FAPs), were developed. FAPs are comprised of two components: a single-chain antibody (SCA) fused to the protein of interest and a malachite-green (MG) derivative, which fluoresces only when bound to the SCA. Importantly, the MG derivatives can be either cell-permeant or -impermeant, thus permitting isolated detection of SCA-tagged proteins at the cell surface and facilitating quantitative endocytic measures. To expand FAP use in yeast, we optimized the SCA for yeast expression, created FAP-tagging plasmids, and generated FAP-tagged organelle markers. To demonstrate FAP efficacy, we coupled the SCA to the yeast G-protein coupled receptor Ste3. We measured Ste3 endocytic dynamics in response to pheromone and characterized cis- and trans-acting regulators of Ste3. Our work significantly expands FAP technology for varied applications in S. cerevisiae.

Optimization of the fluorogen-activating protein tag for quantitative protein trafficking and co-localization studies in S. cerevisiae.

Spatial and temporal tracking of fluorescent proteins in live cells permits visualization of proteome remodeling in response to extracellular cues. Historically, protein dynamics during trafficking have been visualized using constitutively active fluorescent proteins (FPs) fused to proteins of interest. While powerful, such FPs label all cellular pools of a protein, potentially masking the dynamics of select subpopulations. To help study protein subpopulations, bioconjugate tags, including the fluorogen activation proteins (FAPs), were developed. FAPs are comprised of two components: a single-chain antibody (SCA) fused to the protein of interest and a malachite-green (MG) derivative, which fluoresces only when bound to the SCA. Importantly, the MG derivatives can be either cell-permeant or -impermeant, thus permitting isolated detection of SCA-tagged proteins at the cell surface and facilitating quantitative endocytic measures. To expand FAP use in yeast, we optimized the SCA for yeast expression, created FAP-tagging plasmids, and generated FAP-tagged organelle markers. To demonstrate FAP efficacy, we coupled the SCA to the yeast G-protein coupled receptor Ste3. We measured Ste3 endocytic dynamics in response to pheromone and characterized cis- and trans-acting regulators of Ste3. Our work significantly expands FAP technology for varied applications in S. cerevisiae.

Comparative Insecticide Application Techniques (Micro-Sprinkler) Against Drosophila suzukii Matsumura (Diptera: Drosophilidae) in Highbush Blueberry.

Drosophila suzukii (Matsumura), spotted-wing drosophila, is a major pest in small fruit crops including highbush blueberry. Controlling D. suzukii is challenging and chemical control is the main method to manage D. suzukii populations. Growers have expressed interest in using micro-sprinklers as an alternative method to apply insecticides. The current study aimed to evaluate if insecticide applications using micro-sprinklers can be used as an alternative method to protect the fruit from D. suzukii egg-laying. Modeling was used as an additional tool to parameterize the relative insecticide efficacy on oviposition. Field measurements of different treatments were conducted over periods of eleven days on commercial-standard highbush blueberry. Cyantraniliprole and spinetoram were applied using both a micro-sprinkler and a backpack sprayer. Treatments of Chromobacterium subtsugae and zeta-cypermethrin were only applied using a backpack sprayer. Both cyantraniliprole and spinetoram treatments resulted in moderate suppression of D. suzukii egg-laying. No statistical significance was found between micro-sprinkler and backpack sprayer applications for these two insecticides. Zeta-cypermethrin treatments using a backpack sprayer resulted in the most significant suppression of D. suzukii egg-laying over eleven days, while C. subtsugae was less effective at preventing D. suzukii egg-laying. Modeling simulations estimate the impact of the control methods on D. suzukii populations dynamics and simulation outputs indicated that backpack sprayers reduced D. suzukii populations at more pronounced levels compared to micro-sprinkler applications. The present study indicates that there is an underlying value of micro-sprinkler systems as an alternative and rapid spray application technique to help suppress D. suzukii pest populations during high-pressure periods in highbush blueberry production.