The Role of Mitochondrial Alternative Oxidase in Plant-pathogen Interactions

Alternative oxidase (AOX) is a non-energy conserving branch of the mitochondrial electron transport chain (ETC) which has been hypothesized to modulate the level of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in plant mitochondria. The aim of the research presented herein is to provide direct evidence in support of this hypothesis and to explore the implications of this during plant-pathogen interactions in Nicotiana tabacum. We observed leaf levels of ROS and RNS in wild-type (Wt) tobacco and transgenic tobacco with altered AOX levels and we found that plants lacking AOX have increased levels of both NO and mitochondrial O2 - compared Wt plants. Based on the results we suggest that AOX respiration acts to reduce the generation of ROS and RNS in plant mitochondria by dampening the leak of electrons from the ETC to O2 or nitrite. We characterized multiple responses of tobacco to different pathovars of the bacterial pathogen Pseudomonas syringae. These included a compatible response associated with necrosis (pv tabaci), an incompatible response that included the hypersensitive response (HR) (pv maculicola) and an incompatible response that induced defenses (pv phaseolicola). We show that the HR is accompanied by an early mitochondrial O2 - burst prior to cell death. Also, we found iii that the appearance of HR and the appearance of the mitochondrial O2 - burst are delayed in transgenic plants lacking AOX. A similar delay is seen in transgenic plants treated with the complex III inhibitor antimycin A. In Wt plants, expression of Aox1a is suppressed during the HR response to pv maculicola despite the accumulation of signaling molecules known to induce Aox1a transcription. Also, MnSOD activity declined during the HR. We suggest that the mitochondrial ROS burst controlled by AOX and MnSOD is an important component for the induction and coordination of the HR during plant-pathogen interactions.

Department dc:contributor.department

Cell and Systems Biology

Year dc:date.issued

2012

Author dc:creator

• Cvetkovska, Marina

Advisor dc:contributor.advisor

• Vanlerberghe, Greg

• Mitochondria
• Respiration
• Plant pathogens
• Disease resistance

Language dc:language.iso

en_ca

Handle dc:identifier.uri

http://hdl.handle.net/1807/33972

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/33972