Conventional crop protectants (fungicides) can lose their efficacy due to selection pressure for pathogen resistance caused by their widespread use
1. To date, there is a lack of genetic resistance in commercial crop varieties against necrotrophic fungal pathogens
2, such as
Botrytis cinerea. The aggressive fungal pathogen
Botrytis cinerea infects almost all vegetable and fruit crops
3(>1400 plant species), killing the host by inducing necrosis with degradation enzymes (virulence factors) and manipulating its host defences. Non-host inducing agents, such as elicitor molecules, are able to stimulate pathogen-induced defence mechanisms in the plant
4 and induce plant defences for increased and more efficient resistance (priming) against pathogens such as
B. cinerea. Priming is based on a fine-tuned and enhanced resistance to biotic/abiotic stress that results in a faster and stronger expression of resistance upon pathogen attack
5. This study aimed to identify candidate elicitors, determine their mode of action in the plant-
B.cinerea interacion, characterise their molecular function and investigate a candidate elicitor role in priming tomato against
B.cinerea. Resistance phenotypic assays have revealed that chitosan, a MAMP, was able to induced resistance in solanaceous crops
Solanum melongena,
Nicotiana benthamiana,
Solanum lycopersicum and brassicaceous plant
Arabidopsis thaliana by significantly decreasing necrotic lesion sizes and priming for callose deposition in a concentration-dependent manner. Furthermore, large-scale double (host/pathogen) transcriptomic analysis has unveiled that chitosan was able to prime 1,745 tomato transcripts during early and asymptomatic stages of
B. cinerea infection. Transcriptome-based geneontology (GO) enrichment and HPLC/MS analyses revealed that chitosan-priming targets five main clusters, incuding 1) a higher cell sensitization throughout a faster and stronger transmembrane receptor/receptor-like kinase, CaBP and signal transducer activity; 2) a cell-wall reinforcement through R protein activation, cellulose synthesis and PGs, PMEs and xyloglucan repression; 3) a fine-tuned potentiation of JA/JA-Ile synthesis and JA/ET/SA/ABA transcriptional regulation; 4) an induction of the lipid/fatty acid metabolism and phenylpropanoid pathway; and 5) a strong repression of
B. cinerea PGs,
BcSOD, hexokinase and novel virulence factor uracil phosphoribosyltransferase (
BcUPRT).Transcriptome analysis helped to the identification of two tomato novel and co-expressed genes,
SlACRE75 and
SlACRE180. Both transcripts and their
N. benthamiana homologs were primed by chitosan early during infection and encode small proteins without a signal peptide and with unknown functions. Subcellular localization indicates that the four proteins are involved in intracellular/cytoplasmatic signalling. Finally, transient and constitutive overexpression of
SlACRE75,
SlACRE180 and their
N. benthamiana homologs revealed that they are positive regulators of plant resistance against
B. cinerea. Identification of specific chitosan-primed tomato pathways and genes such as
ACRE75 and
ACRE180; and
BcUPRT, will provide a valuable resource for developing novel fungicide use strategies and engineering non-host resistance against necrotrophs in dicots.
| Date of Award | 2018 |
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| Original language | English |
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| Supervisor | Adrian Newton (Supervisor), Nicola Stanley-Wall (Supervisor) & Nicola Holden (Supervisor) |
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