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Published on May 29, 2009; 10.1104/pp.109.139782

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Received April 9, 2009
Accepted May 22, 2009

The transcription factor ABI4 is a regulator of mitochondrial retrograde expression of Alternative oxidase 1a

Estelle Giraud , Olivier Van Aken , Lois HM Ho , and James Whelan *

ARC Centre of Excellence in Plant Energy Biology, MCS Building M316 University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia

* Corresponding author; email: seamus{at}cyllene.uwa.edu.au.

Plant cells integrate signals from external sources and from organelles to regulate gene expression, referred to as anterograde and retrograde signalling respectively. Functional characterisation of the promoter of alternative oxidase AOX1a from Arabidopsis thaliana, a marker for mitochondrial retrograde response, was carried out by testing the ability of the AOX1a promoter to drive expression of the reporter gene {beta}-glucuronidase (GUS). This approach identified a strong repressor element, designated the B element, that was necessary for an increased promoter activity in response to the mitochondrial complex I inhibitor rotenone. This element overlaps with a previously identified potential binding site for the transcription factor abcisic acid insensitive 4 (ABI4). AOX1a promoter activity was fully de-repressed in abi4 mutants, and was unresponsive to rotenone. Furthermore, deletion of the B element of the AOX1a promoter resulted in increased GUS staining activity compared to the wild type promoter in transgenic plants. Binding of the ABI4 transcription factor to this region of the AOX1a promoter was demonstrated by electromobility shift and yeast 1-hybrid assays. Analysis of transcript abundance for AOX1a in abi4 mutant lines revealed significantly increased levels of AOX1a mRNA that could not be further induced by rotenone, consistent with the role of ABI4 as a repressor that is de-repressed in response to rotenone. These results show that ABI4 plays a central role in mediating mitochondrial retrograde signals to induce the expression of AOX1a. Furthermore, they provide a molecular link between mitochondrial and chloroplast retrograde signalling, as ABI4 has been previously shown to act downstream of at least two chloroplast retrograde signalling pathways.






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