Plant Mitochondrial Retrograde Regulation

Abstract

Changes in plant cellular metabolism require altered gene expression. Cellular adjustments and altered gene expression also occur in response to environmental stresses. Both of these situations involve changes in mitochondrial activities. Changes in the status of the mitochondria and resulting inputs for altered nuclear gene expression are communicated to the nucleus by interorganellar signaling called mitochondrial retrograde regulation (MRR). The study of plant MRR is a young field and the mechanisms and components are just beginning to be discovered. Evidence suggests that reactive oxygen species (ROS) can be involved in plant MRR, but this does not mean that they are involved in all cases. Calcium level changes, redox changes, and changes in metabolite levels are leading candidates for nonprotein signaling components. Protein signaling components like kinases, phosphatases, and transcription factors are likely to be involved, but only the recent discovery of the involvement of transcription factor Abscisic Acid Insensitive 4 in Arabidopsis provides a specific protein example. Growing evidence indicates overlaps of MRR with other signaling pathways, including those from chloroplasts. MRR could be linked to metabolic signaling and/or ROS production, but these would still originate in mitochondria and be components of MRR. The emerging view is that plant mitochondria are stress sensors that contribute to decisions regarding cell fate during stresses and that this is conveyed to the nucleus by MRR.