A new understanding of fungal plant pathogens
Fungal pathogens present a widespread and significant threat to global crop production, affecting the yields of many economically relevant plants. Biotrophic fungal pathogens colonise living plant tissue, and secrete proteins known as effectors into the plant to hijack and manipulate cellular processes. Understanding the exact processes by which these fungal pathogens infect plants is critical for future agriculture and food security. Yet synthetically reconstructing eukaryotic plant pathogens is challenging, due to both technological issues and a lack of knowledge. “Eukaryotic pathogens have a very high number of (potential) virulence factors, which are not even close to being understood in their functions,” explains Gunther Doehlemann, professor of Plant Biology at the University of Cologne and conVIRgens project coordinator. Nevertheless, in the conVIRgens project, which was funded by the European Research Council, Doehlemann and his team sought to synthetically reconstruct the virulence strategies of eukaryotic fungal pathogens to better understand how they attack plants.
Using gene editing to dissect fungal virulence strategies
Certain biotrophs such as rusts and powdery mildew are difficult to study, as they are obligate pathogens (and therefore require hosts to fulfil their life cycle), making them tricky to cultivate. Yet some smut fungi, such as Ustilago maydis (the cause of corn smut disease), have a yeast stage, which allows scientists to more easily recreate them in the lab. The original strategy was to disarm U. maydis by mutating the pathogen’s effectors using CRISPR-Cas9 gene editing technology. “We actually have generated multiple CRISPR-Cas9 mutant strains of Ustilago, which are impaired in their virulence and which are used to understand the molecular functions of effector proteins,” says Doehlemann. The team also found an alternative strategy during the project, by successfully constructing a hybrid strain of U. maydis, which they could exploit using CRISPR-Cas9 to uncover the underlying virulence repertoire. Some of the surprising results from this new technique will be available when the research is published later this year.
Practical applications in countering crop yield losses
The conVIRgens team hope their results could benefit the wider scientific community, including through practical applications of the research in countering crop yield losses. “The dissection of the U. maydis effector repertoire actually revealed the set of virulence factors that is needed to generate tumours in plants,” notes Doehlemann. “This was a major goal of the project and we think this is a great benefit for the scientific community.” The project established U. maydis as a tool for functionally characterising effectors from obligate biotrophic fungi, such as rust fungi, and powdery mildew fungi. “Our approach helped to better characterise the virulence arsenals of these organisms, which has a direct implication for research on countering crop yield losses,” he adds.
Future research into the molecular functions of pathogen effectors
The researchers plan to use the knowledge and methods developed in the project to gain more functional insights into the molecular functions of pathogen effectors. A prime example is transcriptional activator effectors, which the team identified in the course of the project. “We will investigate how these effectors function in diverse plant pathogens,” says Doehlemann. The team also discovered that fungal effectors are involved in the competition of fungal pathogens with other microbes, which opened up a new research line the team plans to pursue.
Keywords
conVIRgens, gene editing, fungal virulence, strategies, molecular, functions, pathogens, effectors, CRISPR-Cas9, crop, yield
