ARS | Publication request: PLANT ACONITASE FUNCTIONS AS AN RNA-BINDING PROTEIN AND PLAYS A ROLE IN REGULATING RESISTANCE TO OXIDATIVE STRESS AND HYPERSENSITIVE CELL DEATH

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2006
Publication Date: January 1, 2007
Citation: Moeder, W., Del Pozo, O., Navarre, D.A., Martin, G.B., Klessig, D.F. 2007. Plant aconitase functions as an rna-binding protein and plays a role in regulating resistance to oxidative stress and hypersensitive cell death. Plant Molecular Biology. 63(2): 273-287.

Interpretive Summary: The role hypersensitive cell death plays in restricting a plant pathogen to the initial infection site, and thereby conferring disease resistance is currently unclear. This work identified a protein, aconitase, that appears to be involved in the development of plant disease resistance. Aconitase deficient plants exhibited altered regulation of cell death associated with virulent and avirulent pathogen infection, suggesting aconitase is involved in the activation of both the hypersensitive response and disease-induced plant cell death. Bacteria grew faster in plants with reduced amounts of aconitase. A better understanding of how plants resist disease will assist the development of plants with superior disease resistance that require less pesticide input.

Technical Abstract: 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’-UTR of the Arabidopsis chloroplastic Cu/Zn superoxide dismutase2 (CDS2) mRNA and this binding is specific. Arabidopsis knockout (KO) plants displaying a 20 - 70% reduction in aconitase activity exhibited significantly less chlorosis after treatment with the superoxide-generating compound, paraquat. This 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 significantly altered. VIGS-mediated silenced of aconitase in Nicotiana benthamiana led to a 90% reduction in aconitase activity; these plants were stunted, spontaneously developed necrotic lesions and displayed increased resistance to paraquat. They also exhibited reduced/delayed? HR formation triggered by transient co-expression of the AvrPto and Pto proteins or the proapoptotic protein Bax. By contrast, Cf9/Avr9-induced cell death was unaffected. Following infection with P. syringae pv tabaci (avrPto), aconitase-silenced N. benthamiana plants carrying the Pto transgene displayed a delayed HR that corresponded with an initially greater level of bacterial growth. Unexpectedly, disease-associated necrosis in N. benthamiana inoculated with P. s. pv. tabaci lacking avrPto also was reduced. Taken together, these results suggest aconitase plays a role in resisting oxidative stress and activating cell death, possibly through its RNA binding activity