Figure 6

Proposed scenario for the evolution of the extended LHC protein superfamily. Originating from a cyanobacterial HLIP after the primary endosymbiosis, an endosymbiotic gene transfer resulted in a nuclear-encoded OHP1-like sequence in the common ancestor of Plantae. Such a sequence was likely at the origin of the nuclear-encoded two-helix SEPs that are ubiquitously distributed among photosynthetic eukaryotes. In Viridiplantae and several algae with complex plastids, the plastid-encoded HLIP was transferred to the nuclear genome and subsequently lost in the plastid. The ancestor of the LHC proteins and later of PSBS evolved by independent, internal gene duplication events (indicated by a star*), likely from different SEP groups. The resulting LHC proteins subsequently either lost their fourth TM helix or alternatively they ancestrally never had one. Both, the ELIPs and the RedCAP family are restricted to the green and to the red lineages, respectively. The positioning of the different family names and the background color indicate their taxonomic distribution.