Angelopoulou, Dimitra
(2022)
Understanding the role of photoprotection in
disease resistance to Septoria Tritici Blotch in wheat.
PhD thesis, University of Nottingham.
Abstract
Zymoseptoria tritici, a fungal pathogen of wheat and the causal agent of Septoria Tritici Blotch (STB), is a particular challenge to wheat production on a global level, causing severe crop losses. As the site of photosynthesis, the chloroplast plays a crucial role in energy balance and trade-off between growth demands and response to environmental stresses and it is gaining an ever-growing attention due to its multilayered involvement in disease response and downstream signalling. However, very little is known regarding wheat resistance responses to Z. tritici and the involvement of chloroplastic photoprotection. In the following thesis, I present data indicating the importance of photoprotection, through non-photochemical quenching (NPQ), in disease resistance of wheat plants against virulent and avirulent Z. tritici isolates.
This study presents novel data on wheat plants with increased, “primed” photoprotection resulting in enhanced tolerance towards virulent and avirulent isolates. Plants were over-expressing the photoprotective chloroplastic protein PsbS and maintained a greener phenotype and reduced pycnidia upon inoculation with virulent strains of Z. tritici. Stb6, which encodes a wall-associated kinase protein that confers resistance to Z. tritici isolates expressing the corresponding AvrStb6 effector, has recently been cloned. In this study, I also used Stb6 near-isogenic lines and present findings on the association between the photoinhibitory component of NPQ, qI, and the avirulent isolate IPO323, at 24 hours after inoculation. Transcriptomic analysis also revealed the importance of the oxygen-evolving complex and photosystem II antenna proteins in resistance responses. In contrast, avirulent Z. tritici had no effect on photoprotection; however results indicated a potential virulent strategy that exploits the photosynthetic repair machinery. Also, this study presents early findings on interactions and potential mechanisms of effector-triggered susceptibility from Z. tritici, utilising necrotrophic effectors from another foliar wheat pathogen, Parastagonospora nodorum.
This study represents an important contribution to our understanding of chloroplastic responses to the important pathogen Z. tritici and suggests putative mechanisms of photoprotective, chloroplastic defence. Understanding and incorporating chloroplastic mechanisms into breeding programs could help develop more productive crop plants with a novel durable genetic resistance to plant pathogens.
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