Wheat defence responses induced by the fungal pathogen Fusarium pseudograminearum

Olivia Desmond (2008). Wheat defence responses induced by the fungal pathogen Fusarium pseudograminearum PhD Thesis, School of Molecular & Microbial Sciences, The University of Queensland.

       
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Author Olivia Desmond
Thesis Title Wheat defence responses induced by the fungal pathogen Fusarium pseudograminearum
School, Centre or Institute School of Molecular & Microbial Sciences
Institution The University of Queensland
Publication date 2008-01
Thesis type PhD Thesis
Supervisor Kazan, Kemal
Manners, John
John McLean
Schenk, Peer M.P.
Subjects 270000 Biological Sciences
Formatted abstract Crown rot(CR)of wheat, caused by Fusarium pseudograminearum (Fp) is an important disease globally, resulting in reduced yield as well as contamination with trichothecene mycotoxins, such as deoxynivalenol(DON).This host–pathogen interaction has not been studied previously at the molecular level.To understand the host response to challenge by Fp, we have used the Affymetrix GeneChip Wheat Genome Array to examine gene expression changes in the wheat stem base following inoculation with Fp macroconidia. Induced genes included mainly those with defensive functions, such as genes encoding anti¬microbial proteins, as well as oxidative stress¬related proteins, signalling¬related proteins, and those involved in both primary and secondary metabolism.Expression of selected Fp¬induced genes was confirmed using real¬time quantitative PCR on an inoculation time¬course of two wheat cultivars, Kennedy and Sunco.Interestingly, several genes were induced earlier, and to higher levels, in the partially CR resistant cultivar Sunco than susceptible Kennedy.Many Fp¬induced genes were also induced by methyljasmonate, and treatment with this compound prior to inoculation delayed the development of CR symptoms suggesting thatjasmonates may be involved in activating defences during crown rot.
In this study, the response of wheat tissue to DON has also been investigated.Infusion of wheat leaves with DON induced hydrogen peroxide production within 6h, followed by cell death within 24h that was accompanied by DNA laddering, a hallmark of programmed cell death.Most of the genes identified here as being induced by Fp were also induced by DON in a concentration¬dependent manner.Co¬treatment with DON and the antioxidant ascorbic acid reduced these responses suggesting their induction may be at least partially mediated by reactive oxygen species(ROS), commonly known to be signalling molecules in plants. Taken together, results are consistent with a model where DON production during infection of wheat induces ROS, which on one hand may stimulate programmed host cell death assisting necrotrophic fungal growth, but on the other hand the ROS may contribute to the induction of anti¬microbial host defences.This study is the first comprehensive analysis of wheat responses induced during CR and provides new insights into the host processes potentially involved in wheat defences against Fusarium pathogens.


 
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