Evidence for the importance of hydrogen peroxide in wheat infected by the hemibiotrophic pathogen Septoria triciti
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Infection of wheat by the hemibiotrophic pathogen Septoria tritici (Mycosphaerella graminicola) is accompanied by several defence responses and alterations of the host metabolism. We are comparing expression of defence and the effect of infection on host physiology between a compatible (cv. Sevin-isolate IPO323) and an incompatible (cv. Stakado-isolate IPO323) host-pathogen interaction.
There are no differences in pre-penetration growth and penetration between the two interactions, showing that the defence is active after penetration. One of the earliest defence reactions after a pathogen initiates infection is the oxidative burst, which leads to the production of reactive oxygen species (ROS). ROS have been found to inhibit biotrophic pathogens whereas necrotrophic pathogens are generally believed to benefit or even stimulate
ROS production. We studied the role of hydrogen peroxide (H2O2) in defence as well as a pathogenesis factor for S. tritici. In Stakado (resistant), pathogen growth was arrested just after penetration, resulting in absence of pycnidia and symptoms. The growth arrest coincided with a significantly higher number of autofluorescing cells and accumulation of H2O2 than in the susceptible cv. Sevin. In Sevin, very little H2O2 accumulated, except during sporulation, where tissue degradation occurred. This accumulation probably represents a stress response coinciding with tissue collapse. This pattern of H2O2 accumulation supports the dogma that pathogens with a necrotrophic phase benefit from accumulation of ROS. However, infiltration of catalase (to remove H2O2), water (control) or H2O2 showed that H2O2 was etrimental during all stages of the interaction. Thus, both early (during the initial, biotrophic, stage of infection) and late (during the necrotrophic phase) infiltration of catalase enhanced fungal growth and resulted in faster symptom expression in Sevin whereas infiltration of H2O2 reduced fungal growth and delayed symptom expression [Shetty et al (2007). New Phytol. 174: 637]. Therefore, we provide direct evidence for the role of H2O2 as a resistance factor throughout all stages of the interaction. Among the physiological effects of infection on the host is release of soluble sugars occurring simultaneously with the late H2O2 accumulation in the compatible interaction. The sugar release is related to fungal activity since the pathogen requires nutrients for its reproduction during the necrotrophic phase. ROS accumulation may play several roles in the defence against pathogens such as providing a direct antimicrobial effect and participate in activation of defence-related genes like PRproteins. We are currently investigating these possible roles, among others, from plant material infiltrated with catalase or H2O2 and by the use of catalase knock-out mutants of S. tritici. Likewise, we are studying the sources and regulation of both the early and the late . Likewise, we are studying the sources and regulation of both the early and the late accumulation of H2O2 in this host-pathogen interaction as well as the influence of infection and H2O2 accumulation on host physiology.
|Publication status||Published - 2008|
|Event||The International Mycosphaerella and Stagonospora Symposium - Ascona, Switzerland|
Duration: 18 Aug 2008 → 22 Aug 2008
Conference number: 7
|Conference||The International Mycosphaerella and Stagonospora Symposium|
|Period||18/08/2008 → 22/08/2008|