Tricking plants into starvation responses to gain virulence: Targeting novel effectors of Magnaporthe oryzae by single-cell analysis of infected rice cells and capturing the transcriptome of invasive hyphae.

• Applicant: Professor Dr. Ulrich Schaffrath
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems ; Plant Physiology ; Plant Breeding and Plant Pathology
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 410278620

The pathogen Magnaporthe oryzae is a major threat to important crop plants. The life cycle of the pathogen consists of an initial biotrophic phase, during which the fungus asymptomatically colonizes living host tissue, followed by a necrotrophic phase characterized by the induction of host cell death. The pathogen secretes during both stages molecules, known as effectors, that manipulate host defenses to facilitate infection. Our previous research has demonstrated that M. oryzae secretes a Nudix hydrolase effector (MoNudix) during the transition from the biotrophic to necrotrophic phase. Gene deletion mutants showed a prolonged biotrophic stage, resulting in reduced disease symptoms. This compromised virulence is associated with the induction of the phosphate starvation response (PSR). Similar Nudix effectors are also secreted by other hemibiotrophic pathogens, suggesting that the induction of PSR to suppress plant defense is a conserved virulence strategy. While recent studies have shown that PSR induction in the host also involves Nudix hydrolases and is associated with suppression of defense genes, the link between PSR activation and modulation of plant immunity remains unclear. This project aims to elucidate how M. oryzae and other hemibiotrophic pathogens manipulate host metabolic pathways, such as PSR, to their advantage. Using single-cell transcriptomics, we will analyze gene expression profiles in both the rice host and the invading pathogen. This will resolve the transcriptome of invasive hyphae, which are specialized infection structures formed in host cells during the biotrophic phase. By comparing transcriptome data from M. oryzae wild type isolates and the MoNUDIX gene deletion mutant on different host genotypes, we aim to obtain mechanistic insights into manipulation of metabolic pathways and immune suppression. The project will firstly answer the question whether invasive hyphae of M. oryzae have an infection structure-specific effectome. Because the induction of PSR led only to a quantitatively reduced resistance to M. oryzae, we hypothesize that triggering immune suppression by the concerted activation of multiple starvation pathways is key to full compatibility. Thus, we secondly will address whether other effectors, concomitantly secreted with MoNudix, will activate other metabolic responses such as nitrogen starvation. Thirdly, using single-cell transcriptomics of infected cells from a rice genotype insensitive to MoNudix-induced PSR, we aim to elucidate the link between PSR induction and immune suppression. Here, for functional analyses, and considering time constraints, we will utilize the Arabidopsis / Colletotrichum higginsianum pathosystem as a model. The results of this project will provide a comprehensive understanding of how M. oryzae and related pathogens manipulate host starvation responses to suppress immunity, offering potential targets for the development of sustainable plant protection strategies.

• DFG Programme: Research Grants