Mitochondrial reticulation in shoot apical meristem cells of Arabidopsis provides a mechanism for homogenization of mtDNA prior to gamete formation

Plant mitochondria are typically portrayed as being small, oval organelles. However, a recent study has demonstrated that the chondriome of shoot apical meristem (SAM) cells of Arabidopsis thaliana is unique in having two types of mitochondria, a large, central, tentaculate mitochondrion and variable numbers of small, oval mitochondria in the cell cortex that fuse with and fission from the tentaculate mitochondrion. 1 The tentaculate mitochondrion wraps around the nucleus and persists throughout the cell cycle, undergoing distinct changes in morphology and size in a cell cycle-dependent manner. Here we demonstrate that SAM cell plastids, which also contain DNA, do not reticulate, and address the question as to why SAM cell mitochondria but not plastids form reticulate structures. We postulate that the presence of a large, tentaculate mitochondrion in SAM cells provides an efficient means for homogenizing the mitochondrial DNA and proteins during vegetative life prior to gamete production, and that this mitochondrial architecture prevents speciation. The lack of plastid reticulation in the same cells most likely reflects on the fact that the individual plastids are much larger than the small mitochondria and therefore do not need to fuse to achieve efficient intermixing of their genomes.