Minisymposium 2: Oxidative Stress

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Abs # M0202: Aconitase plays a role in regulating resistance to oxidative stress and pathogen-induced cell death

Presenter:	Moeder, Wolfgang       Contact Presenter
Authors	Moeder, Wolfgang  (A) (B)  del Pozo, Olga  (B) (C)  Navarre, Duroy A (D)   Martin, Gregory B (B)   Klessig, Daniel F (B)
Affiliations:	(A): University of Toronto, Botany Departement (B): Boyce Thompson Institute for Plant Research (C): Instituto de Bioquimica Vegetal y Fotosintesis (D): USDA, Agricultural Research Service

In animals, aconitase is a bifunctional protein. When an iron-sulfur cluster is present in its catalytic center, aconitase displays enzymatic activity; when this cluster is lost, it switches to an RNA-binding protein that regulates the translatability or stability of certain transcripts. Here, we show that plant aconitase may have a similar function as it binds the 5 prime UTR of the Arabidopsis chloroplastic Cu/Zn superoxide dismutase 2 (CSD2) mRNA and this binding is specific. Arabidopsis aconitase knockout (KO) plants were found to have significantly less chlorosis after treatment with the superoxide-generating compound, paraquat. This phenotype correlated with delayed induction of the antioxidant gene GST1, suggesting that these KO lines are more tolerant to oxidative stress. Increased levels of CSD2 mRNAs were observed in the KO lines, although the level of CSD2 protein was not affected. Virus-induced gene silencing of aconitase in Nicotiana benthamiana caused a 90% reduction in aconitase activity, stunting, spontaneous necrotic lesions, and increased resistance to paraquat. The silenced plants also had less cell death after transient co-expression of the AvrPto and Pto proteins or the pro-apoptotic protein Bax. Following inoculation with P. syringae pv. tabaci (avrPto), aconitase-silenced N. benthamiana plants expressing the Pto transgene displayed a delayed hypersensitive response and higher levels of bacterial growth. Disease-associated cell death in N. benthamiana inoculated with P. s. pv. tabaci was also reduced. Taken together, these results suggest that aconitase plays a role in resisting oxidative stress and regulating cell death, possibly through its RNA binding activity.