<P> DNA repair proteins are encoded by the cell's nuclear genome but can be translocated to plastids where they maintain genome stability / integrity by repairing the plastid's DNA . As an example, in chloroplasts of the moss Physcomitrella patens, a protein employed in DNA mismatch repair (Msh1) interacts with proteins employed in recombinational repair (RecA and RecG) to maintain plastid genome stability . </P> <P> Plastids are thought to have originated from endosymbiotic cyanobacteria . This symbiosis evolved around 1.5 billion years ago and enabled eukaryotes to carry out oxygenic photosynthesis . Three evolutionary lineages have since emerged in which the plastids are named differently: chloroplasts in green algae and plants, rhodoplasts in red algae and muroplasts in the glaucophytes . The plastids differ both in their pigmentation and in their ultrastructure . For example, chloroplasts in plants and green algae have lost all phycobilisomes, the light harvesting complexes found in cyanobacteria, red algae and glaucophytes, but instead contain stroma and grana thylakoids . The glaucocystophycean plastid--in contrast to chloroplasts and rhodoplasts--is still surrounded by the remains of the cyanobacterial cell wall . All these primary plastids are surrounded by two membranes . </P> <P> Complex plastids start by secondary endosymbiosis (where a eukaryotic organism engulfs another eukaryotic organism that contains a primary plastid resulting in its endosymbiotic fixation), when a eukaryote engulfs a red or green alga and retains the algal plastid, which is typically surrounded by more than two membranes . In some cases these plastids may be reduced in their metabolic and / or photosynthetic capacity . Algae with complex plastids derived by secondary endosymbiosis of a red alga include the heterokonts, haptophytes, cryptomonads, and most dinoflagellates (= rhodoplasts). Those that endosymbiosed a green alga include the euglenids and chlorarachniophytes (= chloroplasts). The Apicomplexa, a phylum of obligate parasitic protozoa including the causative agents of malaria (Plasmodium spp .), toxoplasmosis (Toxoplasma gondii), and many other human or animal diseases also harbor a complex plastid (although this organelle has been lost in some apicomplexans, such as Cryptosporidium parvum, which causes cryptosporidiosis). The' apicoplast' is no longer capable of photosynthesis, but is an essential organelle, and a promising target for antiparasitic drug development . </P> <P> Some dinoflagellates and sea slugs, in particular of the genus Elysia, take up algae as food and keep the plastid of the digested alga to profit from the photosynthesis; after a while, the plastids are also digested . This process is known as kleptoplasty, from the Greek, kleptes, thief . </P>

What are the 3 types of plastids in plant cells