Degree Name
PhD (Doctor of Philosophy)
Program
Biomedical Sciences
Date of Award
8-2026
Committee Chair or Co-Chairs
Dhirendra Kumar
Committee Members
Tianhu Sun, Ranjan Chakraborty, Robert F. Standaert, Patrick Bradshaw, Gregory W. Bishop
Abstract
Plants are frequently exposed to abiotic and biotic stresses that negatively affect their growth and productivity. To withstand these adverse conditions, plants rely on complex signaling networks involving phytohormones, reactive oxygen species (ROS), and stress-responsive proteins. UDP-glucosyltransferases (UGTs) are key enzymes that regulate small signaling molecules through glycosylation, contributing to stress adaptation and immunity. This study functionally characterized the tobacco UDP-glucosyltransferase enzyme, SIP68, and investigated its role in plant defense, abiotic stress tolerance, and hormonal signaling. In silico analyses confirmed that SIP68 contains a conserved PSPG box typical of family 1 glycosyltransferases and shares strong sequence similarity with plant homologs. SIP68 was found to localize predominantly in the chloroplast and interacts with salicylic acid-binding protein 2 (SABP2), a key regulator of systemic acquired resistance (SAR), as confirmed by Bimolecular Fluorescence Complementation (BiFC) and protein–protein docking analysis. Molecular docking further revealed favorable binding between SIP68 and trans-zeatin, delphinidin, and esculin. Functional analyses of SIP68-silenced tobacco plants demonstrated impaired performance under salinity and osmotic stress, including reduced seed germination, root growth, chlorophyll content, and shoot biomass. Altered catalase and peroxidase activities indicated a role for SIP68 in ROS homeostasis. Under biotic stress, SIP68-silenced plants showed more susceptibility to Tobacco mosaic virus (TMV) and Pseudomonas syringae pv. tabaci, along with compromised SAR, confirming that SIP68 positively regulates SA-mediated defense. Hormonal treatment experiments suggested that SIP68 operates through salicylic acid and cytokinin signaling pathways. Biochemical characterization of recombinant SIP68 expressed in Pichia pastoris and3 analyzed via HPLC-coupled glucosyltransferase assays supported its involvement in trans-zeatin glucosylation and cytokinin homeostasis.
Document Type
Dissertation - embargo
Recommended Citation
Mahmud, Fateh Ali, "Functional Characterization of the Tobacco UDP-Glucosyltransferase SIP68 in Plant Immunity and Growth Responses" (2026). Electronic Theses and Dissertations. Paper 4747. https://dc.etsu.edu/etd/4747
Copyright
Copyright by the authors.
Included in
Biochemistry Commons, Cell Biology Commons, Molecular Biology Commons, Structural Biology Commons
