How fungi colonize plant roots

In nature, plant roots are always colonized by fungi. This interaction can be either mutualistic, benefiting both the plant and the fungus, or pathogenic, where the fungus harms the host plant. A research group led by Professor Dr Alga Zuccaro at the CEPLAS Cluster of Excellence has now deciphered how the beneficial root fungus Serendipita indica successfully colonizes plant roots of the model plant Arabidopsis thaliana. Initially, the fungus colonizes living root cells. Subsequently, limited cell death is triggered in the host plant, facilitating successful colonization without causing significant harm. The mechanisms controlling this host cell death are largely unknown. The team discovered now that Serendipita indica secretes two enzymes, NucA and E5NT, which produce the molecule deoxyadenosine (dAdo). This molecule activates a regulated cell death in plants, enabling the fungus to colonize the root system. The study 'A nucleoside signal generated by fungal endophyte regulates host cell death and promotes root colonization' was published in Cell Host & Microbe.

The researchers show that dAdo is initially produced in the apoplast, an extracellular space outside the host cells. In a subsequent step, dAdo enters the plant cell through the membrane transporter ENT3, where it hijacks the host's immune system to induce cell death. This phenomenon, as described by Professor Zuccaro's team, is not limited to plants. A similar process occurs in human patients during interactions between the pathogenic bacterium Staphylococcus aureus and human immune cells.

'We found that the beneficial root fungus Serendipita indica uses two enzymes to produce dAdo, much like S. aureus, to induce cell death and enable successful colonization. This demonstrates that the mechanism is conserved across different microbes and lifestyles,' said Professor Alga Zuccaro. The findings underscore the crucial interplay between microbial colonization and the host's immune metabolism, paving the way for new strategies in medicine and agriculture. 'By understanding these shared mechanisms, we can develop more effective approaches to manage both harmful and beneficial microbes in human health and crop production.'