It works differently than expected

What happens at the molecular level when plants defend against invading pathogens? Previously, it was assumed that the processes were about the same in all plants. However, such is not the case, as demonstrated by a team of biologists from the Martin Luther University of Halle-Wittenberg (MLU) in a new study published in the scientific journal The plant cell. Researchers studied defense processes in wild tobacco N. benthamiana and found that processes work quite differently than previously thought. The team also described in the study how they discovered this complex interaction using CRISPR / Cas9 genome editing techniques.

When they avoid pathogens, the plants only have their innate immune system on which to fold. "The immune system of a plant is quite simple – special proteins on the surface of plant cells can recognize pathogens and fight them, which induces a weak immune response," says Dr. Johannes Stuttmann of the Institute of Biology MLU. However, some bacteria have found a way to overcome this defense mechanism: they inject so-called effector proteins directly into the plant cell to suppress defense responses. During the course of evolution, the plants have adapted to this trick and have developed other receptor proteins. These proteins recognize the invaders of the cell via the effector proteins and quickly trigger a strong immune reaction. "Since plants do not have immune cells or antibodies, intracellular receptor proteins play a key role in the plant's immune response," says Stuttmann.

Until now, the fundamental principles of plant immune systems have been mainly studied in thals (Arabidopsis thaliana), a relatively simple model organism. The Stuttmann group now wanted to know if these results could also be transferred to the tobacco factory N. benthamiana. According to Stuttmann, his genome is considerably more complex and has not yet been completely sequenced. However, this installation has several advantages that make it interesting for future research.

The team studied a special class of receptors inside the cell, TNL receptors. This class of immune receptors is known to function properly only with a specific protein complex. In order to determine if the same genes are responsible for the immune system of both plant species, the researchers first neutralized several tobacco candidate genes using genome editing techniques and then exchanged genes between the two species. They then checked if the plants were still reacting to parasites. "Unexpected complexity was discovered: a LNP receptor in tobacco also worked in watercress, but this did not apply to the genes in the protein complex.In fact, tobacco plants need a different protein complex Receptor-mediated immune response The signaling pathways for immune responses in different plants seem to vary, "says Stuttmann. This is surprising since it was previously assumed that these processes were largely identical in plants because the proteins involved have changed relatively little during the course of the plant's evolution.

"The widespread notion that the results of Arabidopsis thaliana can easily be transferred to other species often turns out to be wrong," concludes Stuttmann. At the same time, the new study serves to establish N. benthamiana as a model organization for these and other issues.

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Martin Luther University Halle-Wittenberg