Component of the peroxisomal and mitochondrial division machineries. Plays a role in promoting the fission of mitochondria and peroxisomes. Interacts with ARC5. The C-terminus is necessary for mitochondrial or peroxisomal targeting, while the N-terminus is necessary for mitochondrial or peroxisomal fission. Reduced plant growth. Increase in the size of mitochondria and decrease in the number of mitochondria per cell. Overexpression of FIS1A increases the fission of peroxisomes and mitochondria. Belongs to the FIS1 family.