Date of Award

Spring 6-10-2017

Document Type

Honors Project

University Scholars Director

Dr. Jeff Keuss

First Advisor/Committee Member

Dr. Derek Wood

Second Advisor/Committee Member

Dr. Tim Nelson

Keywords

epigenetics, agrobacterium, ti plasmid, acetosyringone

Abstract

The plant pathogen Agrobacterium tumefaciens C58 can transfer a portion of its tumor-inducing (Ti) plasmid to plant hosts in response to the plant wound signals, including Acetosyringone. The portion transferred is aptly titled Transfer DNA (T-DNA) which encode genes involved in tumor production and biosynthesis of a unique bacterial food source called opines that provide an advantage to the inducing Agrobacterium. The Ti plasmid contains a number of genes, including the virulence region that enables T-DNA transfer. Epigenetics investigates how chemical modifications to DNA that don’t alter sequence are used to control gene expression (for example, genes involved in pathogen virulence). Epigenetic modifications can be detected by a next generation sequencing technology called Single Molecule Real Time (SMRT) sequencing. SMRT detects these modifications by tracking kinetic shifts during DNA synthesis. Given the unique inter-kingdom DNA transfer, and the importance of epigenetic regulation in other bacteria and plant species, a comparative exploration of methylation patterns of the Ti plasmid under conditions that induce virulence was undertaken. Over a dozen genes with a variety of purposes (virulence regulation, ion transport, DNA replication, etc.) lost methylation following exposure to the virulence inducing molecule acetosyringone, suggesting increased transcription. Three genes, VirD5, TraM and a phosphate/sodium symporter gained methylation throughout the gene, suggesting down regulation. The patterns discovered, while intriguing, sre limited by possible methodological flaws in SMRT sequencing due to incongruities between reported findings and those described in the literature. A further examination of the expression profiles of these genes is warranted given these findings.

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