During the past decade, it has been recognized that PCD oc- curs virtually in all organisms, including metazoans, plants, fungi, bacteria, and protists. Caspases are cysteine-dependent, aspartate-directed proteases and play a critical role in the reg- ulation of PCD in metazoans. In prokaryotes and most unicel- lular eukaryotes, metacaspases are found associated with PCD
rather than caspases. Cyanobacteria contain a conserved p20- like domain but uniformly lack the p10-like domain in metacaspase. These were termed metacaspase-like proteins (Choi and Berges 2013). The first experimental characteriza- tion of biochemical properties of the caspase homolog gene MaOC1 from the toxic bloom-forming cyanobacterium M. aeruginosa PCC 7806 was expressed in Escherichia coli (Klemenčič et al. 2015). However, little molecular biological information is available on PCD in M. aeruginosa. Experimental evidence for caspase-3-like proteases in cyanobacteria has been obtained primarily from the studies on the effect of adverseen vironmental factors though toin duce PCD such as treatment of the cyanobacterium M. aeruginosa with H2O2 (Ding et al. 2012), exposure of the freshwater cya- nobacterium Anabaena sp. to univalent cation salts (Ning et al. 2002), and subjection of Trichodesmium sp. to iron deprivation and excessive light intensity (Berman-Frank et al. 2004)