|Ray, Suparna - PURDUE UNIVERSITY|
|Urmeev, Fleora - PURDUE UNIVERSITY|
Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2003
Publication Date: December 1, 2003
Citation: Ray, S., Anderson, J.M., Urmeev, F.I., Goodwin, S.B. 2003. Rapid induction of a protein disulfide isomerase and defense-related genes in wheat in response to the hemibiotrophic fungal pathogen Mycosphaerella graminicola. Plant Molecular Biology. 53:741-754. Interpretive Summary: The fungal pathogen Mycosphaerella graminicola, the cause of septoria tritici leaf blotch, is a widespread and economically important pathogen of wheat. Several resistance genes are known, yet the mechanisms that provide resistance are not understood. To identify resistance mechanisms in wheat, gene expression in resistant plants following inoculation with M. graminicola was compared to that in susceptible plants and water-inoculated controls. Analysis of the resulting gene-expression patterns identified a gene, protein disulfide isomerase, which was expressed at higher levels in two wheat lines containing different Septoria resistance genes. Expression of this gene during the resistance response was further confirmed with two additional techniques and by comparison with expression of genes thought to be activated during defense responses in other plants. This is the first gene identified that is correlated with resistance to septoria tritici leaf blotch in wheat. This is also the first report investigating defense-gene expression as a way to characterize early genetic and biochemical events leading to the resistance response of wheat to M. graminicola. This information will be important to plant pathologists and geneticists studying fungal resistance in wheat as it increases our understanding of resistance. It also will be important to plant breeders trying to increase the level of resistance to septoria tritici leaf blotch in wheat because it may provide a molecular marker that can be used to identify resistant plants rather than the time consuming and labor-intensive methods of plant inoculations. This could provide considerable savings in time and resources to wheat breeding programs worldwide.
Technical Abstract: Mycosphaerella graminicola, the cause of septoria tritici leaf blotch, is a widespread and economically important pathogen of wheat. Several resistance genes are known, yet the molecular mechanisms underlying the interaction between this pathogen and wheat are not clearly defined. We performed differential-display (DD) PCR using a resistant cultivar, Tadinia (Stb4 gene for resistance) and the susceptible cultivar Yecora Rojo to identify genes differentially expressed in response to M. graminicola. Among the genes identified by this method was a putative protein disulfide isomerase (PDI). The DD-PCR results were confirmed by Northern analysis and real-time quantitative PCR. For comparison, we similarly monitored the temporal expression of the pathogenesis-related (PR) proteins PR-1, PR-2, and PR-5, and also a putative wheat lipoxygenase, WCI-2. PDI displayed early pathogen responsiveness with maximum expression occurring within 12 hours of inoculation, followed by a sharp decline. Induction was higher in the two resistant lines than in the susceptible line indicating a possible involvement of PDI in the resistance response. The PR genes showed early and very strong resistance-related responses with maximum induction occurring within 12 hours of inoculation. WCI-2 showed low to moderate levels of induction at the earliest time points after which its expression was suppressed in the resistant cultivars. This study has shown that putative defense-related genes are induced very early in response to M. graminicola in wheat, with higher induction levels characterizing the incompatible interactions. Such molecular responses may determine the extent of fungal colonization and ultimately, disease severity.