Gene expression analysis of the wheat response to infection by Fusarium pseudograminearum

Crown rot (CR) of wheat, caused by Fusarium pseudograminearum (Fp) and other Fusarium species, is an important disease globally. To understand the host response to challenge by Fp, we examined gene expression changes in the wheat stem base following inoculation with macroconidia using the Affymetrix GeneChip Wheat Genome Array. Induced genes included mainly those with defensive functions such as genes encoding anti-microbial proteins as well as oxidative stress-related proteins, signalling molecules, and proteins involved in both primary and secondary metabolism. Comparison of genes induced by Fp and the biotrophic rust pathogen Puccinia triticina revealed substantial overlap in most functional classes of induced genes, except for oxidative stress-related genes which were specifically induced by the necrotroph, Fp. Differential expression of selected Fp-induced genes was confirmed and further analysed using real-time quantitative RT-PCR on an inoculation time-course of wheat cultivars Kennedy and Sunco. Interestingly, several genes were induced earlier, and to higher levels, in the partially CR-resistant cultivar Sunco than in susceptible Kennedy. Many Fp-induced genes were also activated by methyl jasmonate and benzothiadiazole, an analogue of salicylic acid, suggesting that these signalling molecules may be involved in activating defences during crown rot. Most of the genes identified here that were induced by Fp were also induced by deoxynivalenol (DON), a toxin produced by Fp during CR. In particular, DON induced several genes encoding glucosyltransferases that may be involved in DON detoxification. To initiate functional characterisation, one of these wheat glucosyltransferase genes was over-expressed in Arabidopsis thaliana, however this did not result in improved tolerance to DON. This study is the first comprehensive analysis of the wheat transcriptome during CR and provides new insights into the host processes potentially involved in plant defence against this pathogen.