Fission and Fusion of Plant Mitochondria, and Genome Maintenance

Abstract

Dynamic changes maintain a multipartite mitochondrial genome meets the changing needs of plant cells.

Figure 1.

Plant mitochondrial fission and fusion. A, Mitochondrial fission (arrows) with a dynamin-related protein, DRP3A (in green; GFP-DRP3A), which localizes to predividing and postdividing sites of mitochondria (in red; stained by MitoTracker) in a tobacco cultured BY-2 cell. Images were made by Dr. Masaru Fujimoto. B, Cell cycle-dependent divisions of organelles. The image shows aligned chromosomes, a dividing plastid, three pairs of divided mitochondria, and a dividing mitochondrion in a part of a dividing Arabidopsis root cell in metaphase. The electron micrograph was made by Dr. Mayuko Sato, Mayumi Wakazaki, and Dr. Kiminori Toyooka. The scale bar is approximate. C, Mitochondrial fusion in an onion (Allium cepa) epidermal cell in which mitochondrial fission was disrupted by coexpression of a dominant-negative type of DRP3B(K56A). Mitochondria matrices were labeled with a photoconvertible fluorescent protein, Kaede, causing some mitochondria to be green and others to be red. Fusion results in a yellow color.

Figure 2.

Mitochondrial genome structures, mitochondrial fusion, and DNA replication. A, In vivo variable-length linear DNA structures with circularly permutated sequences. B, A master circle of the mitochondrial genome deduced from these sequences, although such circles are probably rare. C, Individual mitochondria having zero or some portions of the genome as linear DNA molecules. Double-strand breaks that form linear DNA fragments might be generated by respiration-induced reactive oxygen species. D, Mitochondrial fusion provides an opportunity for recombination of DNA fragments. DNA replication by recombination-dependent replication (RDR) may start at this stage. Fusion is dominant where organellar DNA synthesis is active, such as in shoot apical meristems, and during germination and regeneration.