Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Bernards, Mark A.


Suberin is a heteropolymer comprising a cell wall-bound poly(phenolic) domain (SPPD) covalently linked to a poly(aliphatic) domain (SPAD) that is deposited between the cell wall and plasma membrane. Potato tuber skin contains suberin to protect against water loss and microbial infection. Wounding triggers suberin biosynthesis in usually non-suberized tuber parenchyma, providing a model system to study suberin production. Spatial and temporal coordination of SPPD and SPAD-related metabolism are required for suberization, as the former is produced soon after wounding, and the latter is synthesized later into wound-healing. Many steps involved in suberin biosynthesis remain uncharacterized, and the mechanism(s) that regulate and coordinate SPPD and SPAD production and assembly are not understood. To explore the role of abscisic acid (ABA) in the differential regulation of SPPD and SPAD biosynthesis, I subjected wounded tubers to exogenous treatments including additional ABA, or the ABA biosynthesis inhibitor fluridone. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) expression analysis of SPPD and SPAD biosynthetic genes, coupled with metabolite analyses, revealed that ABA positively influenced SPAD-, but not SPPD-associated, transcript and metabolite accumulation, indicating a role for ABA in the differential induction of wound-induced phenolic and aliphatic metabolism. I took an RNA-seq approach to study broader transcriptional changes that occur during wound-healing. The wound-healing transcriptome time-course illustrated that wounding leads to a substantial reconfiguration of transcription, followed by fine-tuning of responses dominated by suberization. Transcriptome analysis revealed that primary metabolic pathways demonstrate similar temporal expression patterns during wound-healing, but suberin-specific steps display distinct patterns at entire pathway and sub-branch levels. The observed transcriptional changes support a model in which wounding initially alters primary metabolism required to fuel SPPD, and subsequent SPAD, production. This investigation also provided support for uncharacterized biosynthetic steps, and highlighted putative transcription factors and suberin polymer assembly genes (Casparian strip membrane domain proteins and GDSL lipase/esterases) that may play key roles in the regulation and coordination of SPPD and SPAD monomer biosynthesis, polymer assembly and deposition. Overall, my findings offer further insight into the coordination and timing of metabolic and regulatory events involved in wound-healing and associated suberization.

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