The mitochondrial outer membrane AAA ATP ase At OM 66 affects cell death and pathogen resistance in A rabidopsis thaliana

• Published in: The Plant journal : for cell and molecular biology Vol. 80; no. 4; pp. 709 - 727
• Main Authors: Zhang, Botao, Van Aken, Olivier, Thatcher, Louise, De Clercq, Inge, Duncan, Owen, Law, Simon R., Murcha, Monika W., van der Merwe, Margaretha, Seifi, Hamed Soren, Carrie, Chris, Cazzonelli, Christopher, Radomiljac, Jordan, Höfte, Monica, Singh, Karam B., Van Breusegem, Frank, Whelan, James
• Format: Journal Article
• Language: English
• Published: 01.11.2014
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.12665

Summary One of the most stress‐responsive genes encoding a mitochondrial protein in A rabidopsis ( A t3g50930) has been annotated as A tBCS1 ( cytochrome bc1 synthase 1 ), but was previously functionally uncharacterised. Here, we show that the protein encoded by A t3g50930 is present as a homo‐multimeric protein complex on the outer mitochondrial membrane and lacks the BCS 1 domain present in yeast and mammalian BCS 1 proteins, with the sequence similarity restricted to the AAA ATP ase domain. Thus we propose to re‐annotate this protein as A t OM 66 ( O uter M itochondrial membrane protein of 66 kDa). While transgenic plants with reduced A t OM 66 expression appear to be phenotypically normal, A t OM 66 over‐expression lines have a distinct phenotype, showing strong leaf curling and reduced starch content. Analysis of mitochondrial protein content demonstrated no detectable changes in mitochondrial respiratory complex protein abundance. Consistent with the stress inducible expression pattern, over‐expression lines of A t OM 66 are more tolerant to drought stress but undergo stress‐induced senescence earlier than wild type. Genome‐wide expression analysis revealed a constitutive induction of salicylic acid‐related ( SA ) pathogen defence and cell death genes in over‐expression lines. Conversely, expression of SA marker gene PR ‐1 was reduced in atom66 plants, while jasmonic acid response genes PDF 1.2 and VSP 2 have increased transcript abundance. In agreement with the expression profile, A t OM 66 over‐expression plants show increased SA content, accelerated cell death rates and are more tolerant to the biotrophic pathogen P seudomonas syringae , but more susceptible to the necrotrophic fungus B otrytis cinerea . In conclusion, our results demonstrate a role for A t OM 66 in cell death and amplifying SA signalling.