Dongus, Joram Andreas 
ORCID: 0000-0002-8553-6802
(2020).
Structure-Function Analysis of the Central Defence Regulator PAD4 in Arabidopsis.
PhD thesis, Universität zu Köln.
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Abstract
In natural and agricultural environments, pathogens and pests reduce plant growth and fitness. To safeguard global food security in light of climate change, breeders need to generate resistant crop varieties that can withstand invasion of pathogens and pests on a warming planet. For targeted resistance breeding, fundamental knowledge on the plant immune system is essential. However, how these resistance pathways are regulated remains unclear. This thesis aims to expand the knowledge on a central regulator in plant resistance. Plants evolved a sophisticated two-layered immune system to defend themselves against biotic stressors. The first layer of immune responsesis sufficient for plants to defend themselves against the majority of non-host adapted pathogens and pests. However, host-adapted species can colonise the plant by releasing virulence-enhancing effector molecules into the plant cell and repress the plant’s first immune responses. The second immune layer uses intracellular receptors that can recognise these hostile effectors, leading to the activation of a strong immune response in local and distal tissues. In the model species Arabidopsis thaliana, EDS1 and PAD4 proteins together integrate such signals, thereby functioning as an immune signalling hub against various pathogens. PAD4 also limits aphid colonisation by enhancing aphid resistance responses, completely independent of EDS1. EDS1 and PAD4 are present in nearly all seed plants, suggesting a conserved function of these proteins in plant immunity and aphid resistance. EDS1 and PAD4 need to associate with each other to activate resistance pathways and immunity genes. The N-terminal protein domains are required for the EDS1-PAD4 interaction and their C-terminal domains form a cavity. Recent insights in the EDS1 protein structure revealed that several amino acids on the EDS1 side of the cavity are necessary for immune signalling. However, it remains unknown if the PAD4 cavity is required for immune signalling too. To gain functional insights in PAD4 structure-function, I first investigated the properties of the PAD4 N-terminal domain, without its C-terminal domain, and thus without the cavity. This revealed that the PAD4 N-terminal domain is sufficient for resistance to aphids. In contrast, the PAD4 N-terminal domain was insufficient to function with EDS1 in pathogen immunity, supporting the hypothesis that the EDS1-PAD4 C-terminal domains function together in immune signalling. Subsequently, I made single amino acid changes in the PAD4 cavity. This revealed that two independent amino acid changes disable EDS1-PAD4 immune signalling, but did not affect PAD4 aphid resistance. This result highlights that PAD4 immune activities are distinct from PAD4 aphid resistance. Moreover, these findings indicate that EDS1 and PAD4 form a cavity that is essential for immune activation. Although EDS1-PAD4 cavity function remains unknown, it likely forms a signalling surface that functions as a proteininteraction platform, inducing downstream signalling and immune gene activation.
| Item Type: | Thesis (PhD thesis) | ||||||||
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| URN: | urn:nbn:de:hbz:38-467057 | ||||||||
| Date: | 2020 | ||||||||
| Language: | English | ||||||||
| Faculty: | Faculty of Mathematics and Natural Sciences | ||||||||
| Divisions: | Außeruniversitäre Forschungseinrichtungen > MPI for Plant Breeding Research | ||||||||
| Subjects: | Natural sciences and mathematics Life sciences Agriculture |
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| Date of oral exam: | 30 June 2020 | ||||||||
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| Funders: | DFG, Max Planck Gesellschaft | ||||||||
| Refereed: | Yes | ||||||||
| URI: | http://kups.ub.uni-koeln.de/id/eprint/46705 |
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