Wheat can control a fungus to get better plant protection

The research was carried out at the Department of Forest Mycology and Plant Pathology in Uppsala and the Department of Plant Breeding in Alnarp, both at SLU. The study was recently published in the journal BMC Biology.

– The Nobel Prize for the discovery of microRNA highlights how small discoveries can have big consequences. Ambros and Ruvkun's work has laid the foundation for an understanding of gene regulation that we now apply in agriculture. Their discovery is an inspiration in our efforts to develop innovative solutions for crop protection and promote sustainable methods for the future, says Ramesh Vetukuri, one of the SLU researchers behind the study.

Some fungi live as parasites on other fungi, and some of these species have started to be used to control harmful fungi that cause disease in crops. To be able to improve and make this type of biological control more efficient, researchers at SLU are trying to gain a deeper understanding of the mechanisms involved.

A new mechanism for communication

In this work, they have now discovered a completely new mechanism for how plants and fungi communicate. The discovery was made in studies of wheat and the fungus Clonostachys rosea – a parasitic fungus that can attack wheat pests and therefore can be used as a biological pesticide. In addition, this beneficial fungus has properties that promote the growth of wheat.

The communication takes place with the help of small RNA molecules, sRNA, which move from the wheat roots into the fungal cells where they then regulate important genes in the fungus. The wheat can thus switch off, or silence, a gene that affects a certain characteristic of the fungus. This is the very first study where sRNA molecules have been shown to be transported from a plant to a biological control organism.

– This is a big step forward for research into environmentally friendly pesticides in agriculture. If we can influence how the sRNA molecules are sent in the future, we can use it to optimize our crop protection not only in wheat but also in other crops, says Mukesh Dubey.

The wheat controls the effectiveness of the fungus’ defense

The researchers used both microscopy and molecular methods to demonstrate how two different sRNA molecules moved between wheat roots and fungal cells. Once inside the fungal cells, the sRNA switches off important fungal genes. In this case, it was for example a gene that contributes to the production of a protein that helps C. rosea fight harmful fungi.

– The downregulation of the gene suggests that the wheat can control C. rosea's biochemical processes and influence how effective it is as a protection against plant pests. In this case, it may have been more important for the wheat to focus on growth rather than pest control – because there was no pest on the wheat in our study, says Edoardo Piombo.

An enzyme regulates the fungus’ colonization degree

The team also looked at a so-called dicer enzyme that plays an important role in sRNA transport. Dicer enzyme cleaves double-stranded RNA into sRNA. When the researchers produced fungal mutants lacking a dicer enzyme, the colonization of C. rosea on the wheat roots increased. This mechanism thus plays an important role in the regulation of the interaction of the fungus with the wheat roots and it affects both the colonization and the defense mechanisms.

When looking at all the RNA produced, the researchers found that the wheat responds to the beneficial fungus' presence by increasing the activity of genes involved in stress response and defense. At the same time, genes responsible for growth and development were suppressed. This is a well-known trade-off between growth and defense when plants interact with beneficial microorganisms.

– It is very exciting to see how plants and beneficial fungi can communicate in this way. This discovery brings us one step closer to a future where we can develop crops that have stronger defense systems of their own. It would be a perfect way to make biological control organisms more effective and agriculture less dependent on chemical pesticides, concludes Ramesh Vetukuri.