Uncovering the molecular mechanisms of Joka2-mediated plant immunity
File(s)
Author(s)
Arellano Dominguez, Gonzalo
Type
Thesis or dissertation
Abstract
Autophagy is a conserved eukaryotic mechanism essential for cellular homeostasis and immunity. In plants autophagy serves as a crucial defense layer against pathogens. The autophagy cargo receptor Joka2 plays a vital role in plant immunity, particularly in defense against Phytophthora infestans, although its precise mechanisms remain poorly understood.
This thesis investigates the molecular mechanisms through which Joka2 contributes to plant immunity. Using biochemical and cell biological approaches, I characterized three distinct aspects of Joka2 function. First, I demonstrated that Joka2 acts as a scaffolding protein for MAP kinase signaling cascades. Through detailed domain mapping, I showed that MAPK3, MAPK6, and MEK2 all bind to a specific region encompassing the NBR1, bZN, and ZZ domains. The NBR1 domain proved essential for MAPK6 phosphorylation, suggesting Joka2 facilitates signal transduction during immune responses. Second, I uncovered a novel redox-dependent property of Joka2 mediated by its newly identified helical bundle (HB) domain. Unlike its mammalian ortholog p62, Joka2 becomes more soluble under oxidizing conditions. This behavior is triggered by both direct oxidation and pathogen-associated molecular pattern (PAMP) treatment, suggesting a role in early immune responses. Finally, I established that Joka2 regulates defense-related gene expression during immunity. RNA-sequencing and subsequent validation revealed several Joka2-dependent defense genes, including key transcription factors. This regulation requires the NBR1 domain. I also discovered that the resistance Joka2 conferrs against Phytophthora infestans is independent of both the HB domain's redox sensitivity and conserved phosphorylation sites. Surprisingly, I found that Joka2 maintains simultaneous interactions with both autophagy machinery and MAP kinases regardless of immune activation, suggesting parallel rather than switching functions.
Together, these findings reveal Joka2 as a multifunctional protein that integrates autophagy, signal transduction, and transcriptional regulation during plant immunity. This work provides new insights into plant defense mechanisms and suggests potential strategies for enhancing crop resistance to pathogens.
This thesis investigates the molecular mechanisms through which Joka2 contributes to plant immunity. Using biochemical and cell biological approaches, I characterized three distinct aspects of Joka2 function. First, I demonstrated that Joka2 acts as a scaffolding protein for MAP kinase signaling cascades. Through detailed domain mapping, I showed that MAPK3, MAPK6, and MEK2 all bind to a specific region encompassing the NBR1, bZN, and ZZ domains. The NBR1 domain proved essential for MAPK6 phosphorylation, suggesting Joka2 facilitates signal transduction during immune responses. Second, I uncovered a novel redox-dependent property of Joka2 mediated by its newly identified helical bundle (HB) domain. Unlike its mammalian ortholog p62, Joka2 becomes more soluble under oxidizing conditions. This behavior is triggered by both direct oxidation and pathogen-associated molecular pattern (PAMP) treatment, suggesting a role in early immune responses. Finally, I established that Joka2 regulates defense-related gene expression during immunity. RNA-sequencing and subsequent validation revealed several Joka2-dependent defense genes, including key transcription factors. This regulation requires the NBR1 domain. I also discovered that the resistance Joka2 conferrs against Phytophthora infestans is independent of both the HB domain's redox sensitivity and conserved phosphorylation sites. Surprisingly, I found that Joka2 maintains simultaneous interactions with both autophagy machinery and MAP kinases regardless of immune activation, suggesting parallel rather than switching functions.
Together, these findings reveal Joka2 as a multifunctional protein that integrates autophagy, signal transduction, and transcriptional regulation during plant immunity. This work provides new insights into plant defense mechanisms and suggests potential strategies for enhancing crop resistance to pathogens.
Version
Open Access
Date Issued
2025-01-31
Date Awarded
2026-06-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Bozkurt, Tolga
Sponsor
UK Research and Innovation
Publisher Department
Department of Life Sciences
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)