Mitochondrial fusion, division and positioning in plants

Mitochondria are involved in many fundamental processes underpinning plant growth, development and death. Owing to their multiple roles, as the sites of the tricarboxylic acid cycle and oxidative phosphorylation, as harbourers of their own genomes and as sensors of cell redox status, amongst others, mitochondria are in a unique position to act as sentinels of cell physiology. The plant chondriome is typically organized as a population of physically discrete organelles, but visualization of mitochondria in living tissues has shown that the mitochondrial population is highly interactive. Mitochondria are highly motile and movement on the cytoskeleton ensures that the physically discrete organelles come into contact with one another, which allows transient fusion, followed by division of the mitochondria! membranes. This article serves to review our current knowledge of mitochondrial fusion and division, and link this to recent discoveries regarding a putative mitochondrial 'health-check' and repair process, whereby non-repairable dysfunctional mitochondria can be removed from the chondriome. It is proposed that the unequal distribution of the multipartite plant mitochondrial genome between discrete organelles provides the driver for transient mitochondrial fusion that, in turn, is dependent on mitochondrial motility, and that both fusion and motility are necessary to maintain a healthy functional chondriome.