Characterizing the maize Xanthomonas vasicola pv. Vasculorum pathosystem: tissue-specific lifestyles and natural variation in tissue-specific resistance

Xanthomonas vasicola pv. vasculorum (Xvv) is a recently emerged bacterial pathogen of maize. Xvv is formally described as a vascular (xylem-colonizing) pathogen of sugarcane and a nonvascular (mesophyll-colonizing) pathogen in maize. However, there were reports of Xvv infected maize exhibiting symptomology typically associated with vascular pathogens. Understanding the host- and tissue-specificity exhibited by Xvv is important for developing strategies to manage the disease. This research characterizes the interaction between maize and Xvv. Pathogen-associated molecular pattern-triggered immunity (PTI) responses are plants’ first line of defense, and is reviewed in chapter 1. The aim of chapter 2 was to examine the role variation in PTI responses plays in conferring resistance to Xvv in maize. The aim of chapter 3 was to determine the extent to which Xvv can behave as a vascular and nonvascular pathogen in maize and whether resistance to xylem and mesophyll colonization is independently inherited. The aim of chapter 4 was to characterize the transcriptomic differences in maize and Xvv during vascular and nonvascular pathogenesis. To accomplish the aims of the four chapters bacterial transformations, fluorescence microscopy, quantitative trait loci (QTL) mapping, and RNA-seq, were used. The results of chapter 2 did not reveal strong correlations between previously measured PTI responses and resistance to Xvv. However, novel resistance QTL were identified. The results of chapter 3 revealed that Xvv can behave as both a vascular and nonvascular pathogen in maize. Additionally, resistance to Xvv in the xylem and mesophyll is controlled by independently segregating loci. The results of chapter 4 revealed a malectin-like receptor kinase may underlie a major xylem-specific resistance locus to Xvv mapped in chapter 3, suggesting that PTI may have a role in vascular resistance to Xvv. Additionally, Xvv modulates the expression of genes relating to virulence and motility depending on whether the bacteria are living in the xylem or the mesophyll. This research is significant because it highlights the importance of genetic variation in tissue-specific host resistance and in shaping the tissue specificity of bacterial pathogens. Furthermore, the maize-Xvv pathosystem can be developed as a model for understanding the genetic mechanisms underlying tissue-specific resistance and bacterial colonization.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Mullens, Alexander Craig

Contributors dc:contributor

• Jamann, Tiffany
• Hind, Sarah
• Schroeder, Nathan
• Lipka, Alexander

• Tissue-specific host resistance
• pattern-triggered immunity
• Quantitative trait loci mapping
• Dual RNA-seq
• Maize
• Xanthomonas

Statement dc:rights

• Copyright 2025 Alexander Mullens

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129538

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129538