Christian Danve M. Castroverde
Department of Biology, Wilfrid Laurier University
Climate change combined with plant diseases pose serious threats to global agriculture and food security. Because the molecular mechanisms by which environmental factors affect plant immunity and disease are poorly understood, my research program aims to address this critical knowledge gap. We have recently reported that salicylic acid (SA) production is a temperature-sensitive pathway in the plant immune system (Nature Communications 2017 vol 8:1808). SA is an important plant hormone mediating immune responses against a broad range of pathogens.
How elevated temperature intercepts the SA pathway is currently unclear, and strategies to counter temperature-mediated suppression of SA production are also lacking. My continued research into this central biological question has shown that elevated temperature has a profound effect on gene expression of a calmodulin-binding master transcription factor (TF) controlling various immune regulators in plants. Remarkably, constitutive gene expression of this master TF was sufficient to recover SA production and immunity at elevated temperature. Global transcriptome analyses revealed that a significant suite of defense-related target genes were downregulated at elevated temperature. My research has identified a crucial temperature-regulated component of the plant immune system.
The upstream mechanisms involved in temperature regulation of this master TF are unknown. Whether temperature-sensitive immunity observed in the model plant Arabidopsis thaliana occurs in other plant species is also unclear. These are important next-level questions that I am currently investigating. By integrating molecular, genetic and biochemical approaches, my research program aims to understand plant-pathogen interactions in a dynamically changing environment, in order to shed light on plant resilience mechanisms.
Special time and place, Room 3110 at 3:30 PM.
The use of plants to remediate contaminated lands is of growing interest to the scientific community because of its ease of implementation, cost effectiveness and ability to stabilize contaminated soils. A novel Populus tremula x Populus alba mutant named fuzzy with an increased trichome density, an elevated growth rate, enhanced pest resistance and a predicted root phenotype was investigated for its ability to tolerate and accumulate arsenic and cadmium in soil. The chlorophyll, hydrogen peroxide and proline contents of fuzzy tissues were assayed, its tissue metal content was measured using ICP-MS and its wet biomass was quantified. Transgenic Arabidopsis thaliana overexpressing homologous gene of that overexpressed in the fuzzy poplar were grown on gel media and their roots were measured to corroborate the root phenotype of fuzzy poplars. The fuzzy poplar was found to have lower levels of hydrogen peroxide in its tissues after arsenic and cadmium exposure than control poplars, suggesting it has a reduced oxidative stress response when exposed to high levels of arsenic and cadmium. This low hydrogen peroxide content was not due to reduced arsenic and cadmium accumulation in fuzzy trees, as they did not accumulate different amounts of arsenic or cadmium than control plants. Proline and chlorophyll levels were not significantly different between metal treatments, or between fuzzy and control poplars. fuzzy poplars exhibited significantly higher root biomass than control poplars, and transgenic Arabidopsis thaliana overexpressing a homologous gene to the one that causes the fuzzy phenotype had significantly longer roots than control plants. All poplars exposed to arsenic and cadmium in this trial contained the majority of these compounds in their tissues in roots. The root biomass phenotype, low hydrogen peroxide content and root metal accumulation in the fuzzy poplar make it an ideal candidate for bioremediation and soil stabilization of contaminated soils.
Tuesday Sept. 17 // Driving metabolic flux and avoiding carbon loss; lessons from opiate alkaloid biosynthesis
Department of Biological Sciences,
Brock University, St. Catharines, ON
Opium poppy has been in use as a medicinal plant since before the dawn of civilization. Today, it remains the only source for natural opiate analgesics, codeine and morphine, and precursors used to synthesize derivatives such as the overdose antidote, naloxone. Total chemical synthesis of opiates is not commercially feasible due to complex stereochemistry. Engineering microbes with alkaloid biosynthetic machinery from opium poppy has the potential of providing a sustainable global supply of opiate pharmaceuticals. However, microbial bioproduction often suffers from carbon loss to alternative pathways. In the latter stages of opiate biosynthesis, thebaine is converted, via codeine, to morphine. When this pathway is simulated in vitro or in microbial systems, two undesirable isomers accumulate: neopine and neomorphine. We addressed this aberrant pathway in two studies: 1) In the penultimate step of morphine biosynthesis COR reduces codeinone to codeine. However, codeinone exists in an apparent equilibrium with its isomeric form, neopinone. We showed that COR irreversibly reduces neopinone to neopine. Using natural and synthetic protein variation we also identified four residues that can confer COR with higher protein stability and performance, improving metabolic flux. 2) We sought an explanation for why the plant does not accumulate the isomeric byproducts. Using a proteomics approach, we found a novel enzyme, neopinone isomerase (NISO) that catalyzes the assumed spontaneous conversion of neopinone to codeinone. NISO provides the substrate for COR to produce codeine and precludes the formation of neopine. Inclusion of NISO in yeast strains engineered to convert thebaine to natural or semisynthetic opiates dramatically enhances formation of the desired products and avoids carbon loss.