Does the N-end rule pathway of targeted proteolysis control the plant immune system?

This project will investigate the role of the N-end rule pathway of targeted proteolysis in the plant response against pathogens. Through advanced proteomics and transcriptomics approaches we aim to identify protein substrates regulated by a specific branch of the N-end rule pathway and investigate their role in the defense response. We will analyse new N-end rule associated genetic resources in barley that should increase resistance to pathogens. This work will provide evidence for a novel post-translational mechanism within the plant immune response, and resources to develop crops with increased resistance to pathogens.

The capacity of plants to survive adverse conditions and reach reproductive maturity critically depends on their ability to continuously adapt to changes in the environment, particularly in response to pathogens. Many studies have identified the control of protein stability as a major regulator of plant responses during invasion and propagation of pathogens, showing that modulation of the stability of key regulatory proteins is required for adaptation to pathogenic infections. The N-end rule pathway of targeted proteolysis is a Ubiquitin Proteasome System mechanism that controls protein degradation dependent on the N-degron, a specific motif mainly determined by an N-terminal (Nt-) destabilizing amino acid residue, targeting the proteins for degradation . This pathway has been extensively studied in animal and yeast systems, where it was shown to have an important role in developmental processes, including apoptosis. Recently in our group the first plant physiological substrates of the N-end rule pathway were identified (the GroupVII ERF transcription factors), that were shown to be the major regulators of plant oxygen and nitric oxide (NO) sensing, through the Cysteine-Arginine branch of the pathway (Cys-Arg/N-end rule pathway) . Our recent unpublished experiments clearly show that in Arabidopsis the N-end rule pathway is involved in the regulation of the immune response, revealing the importance of an as yet undiscovered substrate(s) with Nt-Glutamine (Q) of a separate branch of the pathway that utilizes the enzyme Glutamine Amidohydrolase (NtQ-amidase; NTAQ). This is the first time that a function for this branch of the pathway has been discovered in plants. Our overarching hypothesis for this work is that the N-end rule pathway mediates previously undiscovered key aspects of plant responses to pathogens by controlling the stability of specific substrate proteins with N-terminal Glutamine.

Who will benefit from this research?

Beyond academic audiences where the impact is obvious in terms of increased understanding of how protein degradation controls plant pathogen responses, the major beneficiaries of the work described in this proposal will be the commercial private sector and the wider public, and perhaps ultimately the farming sector.

How will they benefit?

If successful our research could in the future lead to the production of crops that have altered characteristics associated with increased resistance to biotic stresses.

The commercial arm of our University recognises the importance of our findings and are already engaged in applying for a patent to protect the results arising from our earlier work on the role of the N-end rule pathway in regulating abiotic stress in plants. We will continue to discuss our results with appropriate commercial end users whenever possible to inform them of our findings. For example, we will have a display at Cereals, the leading technical event for the UK arable industry which attracts approximately 30,000 visitors annually.

A wider commercial user group have the potential to benefit as our project will train highly skilled workers for the workforce. We will produce scientifically and computer literate researchers, with excellent oral and written presentational skills.

Engaging with the wider public will be undertaken by all of the investigators and researchers employed on the project. We believe that through our efforts the general public will benefit from a greater knowledge of how plants work and an understanding of how tax payers' money is being used to help contribute towards global food security. To engage with this wider sector of end users, the aims of our work will be presented to visitors to our institution (for example during science week events, university open days and graduation celebrations). We will produce a series of display boards aimed at introducing the general public to the requirement for food security, the need to produce crops with improved agronomic traits, and to outline how modifying gas sensing is likely to impact on this process.