H2020 FOUNDATION Project: Fusarium oxysporum-mediated basis of cell-type-specific modulation of multi-host interactions
- Type Project
- Status Filled
- Execution 2018 -2020
- Assigned Budget 170.121,6 €
- Scope Europeo
- Main source of financing H2020
- Project website FOUNDATION
Since F. oxysporum grows primarily intercellularly during its early stages, we hypothesized that the pathogen might secrete pathogenicity proteins, known as effectors, into this intercellular space to determine overall compatibility and manage host immunity. As part of my MSCA fellowship, I primarily established the isolation of apoplastic fluid from infected tomato roots and used discovery proteomics to identify effectors.
These identified “core apoplastic effectors” encode hypothetical small, secreted, cysteine-rich proteins that are conserved across the Fusarium species complex (Redkar et al., in prep.). These core effectors, termed (ERC: Effector for Root Compatibility ERC1-3), are induced in planta upon host/non-host colonization and contribute to virulence. I also performed a comprehensive RNA-Seq analysis during the early stages of F. oxysporum colonization and found that a significant proportion of the secretome encodes primarily effectors that are conserved across the Fusarium-specific complex. This suggests that Fusarium relies on a conserved repertoire of effectors to establish compatibility in hosts and non-hosts, and then host-specific determinants may primarily play a role in determining wilting, which is host-specific.
We also investigated the nature of the active intercellular root proteome during Fusarium colonization and how its activity triggers defense signaling. Infected apoplastic fluid was used for Activity-Based Protein Profiling (ABPP), which indicated that Fusarium is capable of suppressing different classes of proteases. Based on these findings and our interest in apoplastic immunity, I led a featured research article in Trends in Plant Science (doi.org/10.1016/j.tplants.2019.06.009). The article highlights work on the Ustilago maydis effector Pit2, which has a protease inhibitory domain and mimics the protease substrate. Additionally, I co-authored a review on the current knowledge of the molecular interactions of smut fungi and their hosts in Annual Reviews (doi: 10.1146/annurev-phyto-082718-100139). This has influenced ongoing research in the field of plant-pathogen interactions.
Furthermore, I have used the Arabidopsis-Fusarium pathosystem to understand the host-derived signals that the fungus detects upon reaching the xylem. The root endodermis is a protective cellular layer that separates the cortical zone and the vasculature. The space between endodermal cells is permeated with a lignin-based hydrophobic polymer, termed the Casparian band (CS), and acts as a selective barrier. Cell wall-associated membrane proteins (CASPs) fuse to form a continuous band that is guided by the well-defined Schengen pathway (SGN). I hypothesize that vascular wilts likely interfere with different components of the SGN pathway to sense the vasculature. We used a collection of Arabidopsis mutants in the SGN pathway, which display varying degrees of pathogenicity phenotype with F. oxysporum Fo5176. Therefore, the CS pathway appears to be involved in guiding Fusarium to the vasculature. The results of my project were presented in research seminars at the CEPLAS Fellows Conference at the University of Düsseldorf (Germany) and IISER (Pune, India).
Moving forward, I will continue in my host laboratory thanks to the Juan de la Cierva fellowship. I am working on the functional characterization of the CORE effectors identified in Fusarium. I will also explore the intriguing insights into Fusarium's interference with the Casparian Strip pathway in vascular sensing. Upon completion, my goal is to publish two research papers detailing my findings.
In addition to the proposed work, I was also the corresponding author on two commentary articles: one describing how root pathogens have evolved to target master transcriptional regulators of the salicylic acid pathway (doi: 10.1098/rstb.2015.0459) and another providing an overview of how pathogens have evolved to utilize transporter proteins for virulence functions (doi: 10.1111/nph.14137).
Pathogenic fungi have a drastic impact on human nutrition by reducing crop productivity. Many fungal-plant interactions occur in the soil and crucially affect plant health. Very little is known about how soil-borne pathogens infect roots and impair host immunity. A particularly destructive group of root-infecting fungi causes vascular wilt, which attacks many crops, colonizes the roots, and causes progressive wilting. These diseases are among the most difficult to control, as the pathogens are often inaccessible to chemicals present in the roots. Therefore, they are controlled with nonspecific spray compounds that have a detrimental effect. To develop a sustainable solution against these fungi, it is crucial to fully understand how these pathogens establish compatibility with various hosts and the plant processes they target.
The fungal genus Fusarium contains many soil-borne pathogens that cause wilt diseases in numerous crops. Currently, there is little information about the crucial biotrophic infection stage (life phase) of Fusarium. The fungus penetrates roots and eventually colonizes the xylem, resulting in death or absence of death, and even endophytic lifestyles. Therefore, Fusarium is an excellent model for investigating multihost compatibility and immunosuppression. Controlling soil-borne plant pathogens is very difficult due to their high persistence and remarkable ability to adapt to the host plant and the environment.
Since most soil-based fungicides are banned by EU legislation, there is an urgent need to develop new control strategies that are efficient, long-lasting, and environmentally friendly. Identifying the molecular events that underpin disease development in diverse hosts addresses the long-standing question of how these fungi sense the host vascular system. This is of fundamental interest in microbial interactions. The overall objective of my proposal is to understand the mechanisms underlying plant colonization by F. oxysporum to conquer a wide range of hosts. I hypothesize that alteration of the intercellular space (apoplast) where the pathogen primarily resides during biotrophic stages in the host/non-host will serve as a site of action for "core" pathogenicity determinants to colonize a broad spectrum of agronomically important crops.
Fungi have a devastating impact on human nutrition and health. Each year, pathogenic fungi cause enormous agricultural losses in crop plants and contaminate food with harmful mycotoxins. The soil-borne fungal pathogen, Fusarium oxysporum, infects plant roots and vascular tissue, causing wilt diseases in more than 100 different crops, including dicots and monocots. A particularly aggressive strain of this pathogen, tropical race 4, is threatening banana plantations worldwide. Currently, there is little information on the crucial stage of biotrophic infection by vascular pathogens, from root penetration to xylem vessel colonization. Fusarium provides an excellent model for investigating the detection, adaptation, and suppression of plant immunity specific to cells related to the early stages of infection. The host group recently reported on the chemotrophic sensing mechanism used by this pathogen and identified the host plant cues perceived by Fusarium in the soil. Furthermore, their work revealed a combined action of enzymes involved in fungal cell wall remodeling and plant cell wall degradation, which contributes to the virulence of this pathogen. In this project, we aim to identify the cell-specific virulence genes that F. oxysporum uses to colonize a dicot (Arabidopsis) versus monocot (Banana) host that has fundamentally distinct vascular tissue architecture. We will use dual RNA-Seq coupled with laser capture microdissection (LCM) to identify core compatibility components in both the pathogen and the plant, which are essential for establishing the wilt disease. This will lead to the identification and characterization of potential targets in this interaction that could be used to develop new resistance strategies in ongoing banana breeding efforts. Therefore, this project will advance fundamental knowledge of how a fungus senses and colonizes such a wide range of hosts, while creating new opportunities for crop protection by dissecting the interaction at cell-type-specific resolution.
The findings of my MSCA project have generated new insights into the colonization strategies of root pathogens. The identification of conserved effectors in Fusarium that likely mediate compatibility will allow us to better understand the molecular mechanisms underlying the requirement for a short biotrophic phase in the pathogens' life cycle. Furthermore, identifying the plant apoplastic processes that pathogens like Fusarium manipulate will provide new avenues for understanding molecular interaction and contribute to the development of resistance. Overall, I believe the results of my project will have broad implications, as they offer a first glimpse into the crucial asymptomatic infection phases of these important fungal pathogens.
Likewise, by promoting my research through general articles and interacting with school students via Skype with Scientist, I've been able to reach a broader audience. This has provided me with an excellent platform to promote my work and make my research known to the public. Furthermore, my participation in conferences has allowed me to expand my professional network, increasing my opportunities to become a successful principal investigator.
- UNIVERSIDAD DE CORDOBA (UCO)
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