Molecular mechanism of plant immune receptors discovered

December 07, 2020

In a recent study, Alexander von Humboldt Professor Jijie Chai at the University of Cologne and his team together with MPIPZ researchers have succeeded for the first time in reconstructing the sequence of molecular events that activate an inactive plant immune receptor and thus mediate the death of the host cell. The researchers' discoveries are of great importance for understanding how these critical plant immune molecules protect their hosts from infections. The configuration adopted by the activated protein is similar to that of other plant and mammal receptors, including humans. This suggests that these receptors are based on a common structural principle to trigger intracellular immune signals and cell death in different areas of life.

The scientists describe their results in the article 'Direct pathogen-induced assembly of an NLR immune receptor complex to form a holoenzyme' in Science.

Although separated by millions of years of evolution, plants and animals have independently developed similar immune strategies to protect themselves against microbial infections. In both kingdoms of life, immune receptors called nucleotide-binding/leucine-rich repeat proteins (NLR proteins) form an important defence layer within cells against pathogen attack. NLRs are complex devices consisting of several modules. These modules recognize the molecules (effectors) of invading microbes. Effectors trigger the immune response of the plant - they activate receptors, resistance and cell death pathways to limit infection. Based on different structural and signalling characteristics, plant NLRs are divided into two main classes: those that contain coiled-coiled (CC) modules (CNL proteins) and those that contain toll/interleukin-1 receptor/resistance (TIR) modules (TNL proteins).

The scientists conducted their research on the model organism Arabidopsis thaliana, or thale cress. Jijie Chai, together with the MPIPZ research group leader Jane Parker and MPIPZ dirctor Paul Schulze-Lefert, determined the structural and biochemical features underlying the activation of a specific receptor: the so-called TNL type NLR Receptor of Peronospora parasitica 1 (RPP1). It protects the model plant against infection with the fungus Hyaloperonospora arabidopsidis (Hpa).

To understand how RPP1 protects plants on the molecular level from Hpa infection, the team generated RPP1 protein together with the known Hpa effector ATR1 . The RPP1 receptor activated in this way is an enzyme that breaks down nicotinamide adenine dinucleotide (NAD+), which is important for defence signalling.

By isolating RPP1-ATR1 complexes and subjecting them to cryo electron microscopy, the authors have answered two open questions of NLR biology: first, how direct binding of the effector to the NLR receptor induces the activation of a receptor. Secondly, they determined that the TNL receptor in this case organizes itself as a so-called tetramer, a molecule consisting of four tightly packed receptor molecules. Tetramers belong to the group of oligomeric molecules, which are all structurally made up of similar units. The observed tetramer creates a unique surface within a part of the receptor, which is necessary for the cleavage of NAD+ to trigger defence signals.

The effector ATR1 induces tetramerization at one end of RPP1 and simultaneously forces the above-mentioned four TIR modules at the opposite end of the molecule to form two asymmetric TIR pairs that degrade NAD+.

Strikingly, the results of the groups around Eva Nogales and Brian Staskawicz at the University of California, Berkeley, on another NLR of the TNL type, Roq1 from the tobacco relative Nicotiana benthamiana, also show that TNL activation involves direct effector recognition and adoption of a similar tetrameric structure. The effector recognized by Roq1 is produced by a bacterial pathogen and the activated Roq1 receptor complex provides resistance to bacterial infections. Therefore, the discoveries of Jijie Chai, his team and the MPIPZ researchers seem to be of great importance for understanding how these critical plant immune molecules protect their hosts from infections. More generally, the oligomeric configurations adopted by active RPP1 and Roq1 resemble the induced oligomeric scaffolds of other plant and mammalian NLR receptor proteins, including human innate immune receptors. This suggests that these receptors are based on a common structural principle to trigger intracellular immune signals and cell death in different kingdoms of life.

University of Cologne

Related Cell Death Articles from Brightsurf:

Cell death in porpoises caused by environmental pollutants
Environmental pollutants threaten the health of marine mammals. This study established a novel cell-based assay using the fibroblasts of a finless porpoise stranded along the coast of the Seto Inland Sea, Japan, to better understand the cytotoxicity and the impacts of environmental pollutants on the porpoise population.

Gold nanoparticles to save neurons from cell death
An international research team coordinated by Istituto Italiano di Tecnologia in Lecce (Italy) has developed gold nanoparticles able to reduce the cell death of neurons exposed to overexcitement.

New light shone on inflammatory cell death regulator
Australian researchers have made significant advances in understanding the inflammatory cell death regulatory protein MLKL and its role in disease.

Silicones may lead to cell death
Silicone molecules from breast implants can initiate processes in human cells that lead to cell death.

New players in the programmed cell death mechanism
Skoltech researchers have identified a set of proteins that are important in the process of apoptosis, or programmed cell death.

Tumors hijack the cell death pathway to live
Cancer cells avoid an immune system attack after radiation by commandeering a cell signaling pathway that helps dying cells avoid triggering an immune response, a new study led by UTSW scientists suggests.

How trans fats assist cell death
Tohoku University researchers in Japan have uncovered a molecular link between some trans fats and a variety of disorders, including cardiovascular and neurodegenerative diseases.

Bacteria can 'outsmart' programmed cell death
To be able to multiply, bacteria that cause diarrhoea block mediators of programmed cell death, a new study in 'Nature Microbiology' shows.

Cell death or cancer growth: A question of cohesion
Activation of CD95, a receptor found on all cancer cells, triggers programmed cell death -- or does the opposite, namely stimulates cancer cell growth.

Cell death blocker prevents healthy cells from dying
Researchers have discovered a proof-of-concept drug that can prevent healthy cells from dying in the laboratory.

Read More: Cell Death News and Cell Death Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to