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UBC Theses and Dissertations

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UBC Theses and Dissertations

Investigating Golgi retrograde dynamics through the xylan synthase complex in Arabidopsis thaliana Arnott, Araliya Kenzie

Abstract

Xylan is a key hemicellulose in the plant secondary cell wall that contributes to structural integrity. As the third most abundant biopolymer in the world, xylan is an environmental cornerstone in woody species, thus it is important to understand the proteins that manufacture xylan. The xylan synthase complex (XSC), the enzymatic complex responsible for manufacture of the xylan backbone, is a group of Golgi resident proteins that maintains its position in the medial to trans-Golgi through unknown Golgi retrograde activity. To evaluate potential models of retrograde activity, two prevalent endomembrane transport systems were investigated: inter- Golgi tubule connections and coat protein 1 (COPI) vesicles. The effect of COPI vesicle inhibition was assessed by measuring secondary cell wall deposition and the growth phenotype of mutants of the small GTPase ARF1, which is required for COPI vesicle recruitment. COPI inhibition did not impact secondary cell wall formation. The drug brefeldin A (BFA) was also used to inhibit COPI vesicle formation, and the effect monitored with live cell imaging, but no change in the xylan biosynthetic enzyme was observed. Golgi resident protein dynamics were also investigated to determine the ability for proteins to move between Golgi stacks. Using a photoconvertible fluorophore, mEos, tagged to a component of the XSC, IRREGULAR XYLEM 9 (IRX9), sub-populations of the protein complex in individual Golgi could be tracked within a single cell. This tracking revealed the ability for resident proteins to move across Golgi stacks through an unknown trafficking method. This research reframes inter-Golgi trafficking models away from COPI and highlights the possibility that xylan biosynthetic enzymes can move between the scattered stacks of the plant Golgi.

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