Mapping xylan biosynthesis in plant Golgi and teaching biology using example answers

Secondary cell walls (SCWs) containing the hemicellulose xylan are essential for normal plant growth and development. Great strides have been made to identify the many Golgi-localized biosynthetic enzymes that work in concert to make xylan, however, we still understand little about how these critical proteins and their product are organized in the Golgi to facilitate synthesis and trafficking. To address this question, I characterized the Arabidopsis Golgi in cells producing SCWs using a combination of confocal and transmission electron microscopy (TEM). This analysis indicates that the number of Golgi stacks increases significantly with the onset of SCW synthesis, and that during this process the randomly distributed Golgi stacks work together to produce and secrete xylan. Furthermore, nanoscale characterization of Golgi structure revealed significant increases in Golgi diameter, swelling of the cisternal margins, and secretory vesicle size. Loss of the xylan-biosynthetic enzyme IRREGULAR XYLEM 9 (IRX9) resulted in a dramatic increase in cisternal fenestration and a decrease in swollen margins, but did not affect the number or size of Golgi. Finally, immunogold labelling was used to map IRX9-GFP and xylan to different regions of Golgi cisternae, indicating that xylan is abundant in the outer margins of trans-cisternae, IRX9-GFP is abundant in an inner margin of medial-cisternae, and both are absent from cisternal centers. This new concentric circle model of Golgi organization has expanded our understanding of Golgi structure and function and has implications for Golgi function in other cell types and organisms. The second part of this thesis explores problem-solving instruction in undergraduate cell biology classes, by testing how different teaching techniques affect student attitudes and performance. These results demonstrate that worked examples can be effective teaching techniques for cell biology problem-solving, with lower-performing students seeing greater benefits. Furthermore, providing worked examples did not ameliorate student desires for answer keys to practice problems. This work can be used to guide the appropriate level of instructional support for students of different expertise levels in future courses, and across curricula.Science, Faculty ofBotany, Department ofGraduat

Engaging Education for Public Good

Webcast sponsored by the Irving K. Barber Learning Centre. How can education make a positive contribution in and out of the university? Faculty of Education Public Scholars Initiative (PSI) students Ron Darvin and Sereana Naepi and five of their PSI colleagues have seven minutes each to explain their research in this area.Education, Faculty ofGraduate and Postdoctoral StudiesUnreviewedFacultyPostdoctora

Influence of water deficit on the molecular responses of Pinus contorta?×?Pinus banksiana mature trees to infection by the mountain pine beetle fungal associate, Grosmannia clavigera

Conifers exhibit a number of constitutive and induced mechanisms to defend against attack by pests and pathogens such as mountain pine beetle (Dendroctonus ponderosae Hopkins) and their fungal associates. Ecological studies have demonstrated that stressed trees are more susceptible to attack by mountain pine beetle than their healthy counterparts. In this study, we tested the hypothesis that water deficit affects constitutive and induced responses of mature lodgepole pine × jack pine hybrids (Pinus contorta Dougl. ex Loud. var. latifolia Engelm. ex S. Wats. × Pinus banksiana Lamb.) to inoculation with the mountain pine beetle fungal associate Grosmannia clavigera (Robinson-Jeffrey and Davidson) Zipfel, de Beer and Wingfield. The degree of stress induced by the imposed water-deficit treatment was sufficient to reduce photosynthesis. Grosmannia clavigera-induced lesions exhibited significantly reduced dimensions in water-deficit trees relative to well-watered trees at 5 weeks after inoculation. Treatment-associated cellular-level changes in secondary phloem were also observed. Quantitative RT-PCR was used to analyze transcript abundance profiles of 18 genes belonging to four families classically associated with biotic and abiotic stress responses: aquaporins (AQPs), dehydration-responsive element binding (DREB), terpene synthases (TPSs) and chitinases (CHIs). Transcript abundance profiles of a TIP2 AQP and a TINY-like DREB decreased significantly in fungus-inoculated trees, but not in response to water deficit. One TPS, Pcb(+)-3-carene synthase, and the Class II CHIs PcbCHI2.1 and PcbCHI2.2 showed increased expression under water-deficit conditions in the absence of fungal inoculation, while another TPS, Pcb(E)-β-farnesene synthase-like, and two CHIs, PcbCHI1.1 and PcbCHI4.1, showed attenuated expression under water-deficit conditions in the presence of fungal inoculation. The effects were observed both locally and systemically. These results demonstrate that both constitutive and induced carbon- and nitrogen-based defenses are affected by water deficit, suggesting potential consequences for mountain pine beetle dynamics, particularly in novel environments