Figure 1.

Maximum likelihood phylogenies of FRL-PSII subunits. The PsbA phylogeny has been rooted at the point of divergence of Group 1 sequences as categorized by Cardona et al. [37]. Together with Group 0 and Group 2, these make the “atypical” forms of PsbA characterized by the erosion of the ligand sphere of the water oxidizing cluster. Group 3 and Group 4 include all sequences with a conserved ligand sphere and that can support water oxidation function. In this phylogeny, Group 3 has been split into several subgroups, while the G0 sequences are artificially clustered within Group 2. The MRCA of cyanobacteria (green circle) is defined in this instance as the point in Group 4 PsbA, which contains all standard PsbAs, including those found in the basal genera Gloeobacter and close relatives (Anthocerotibacter/Aurora): order Gloeobacterales. For all other subunits, the trees have been rooted at the branching point of Gloeobacterales, and therefore the MRCA of cyanobacteria (green circle) is defined as the last shared ancestor between this and all other lineages. The MRCA of all FRL sequences is marked with an orange circle and it is defined as the last shared ancestor of all extant FRL sequences.