Evolution of oxygenic photosynthesis - New D1 sequences

Early this year I published a study on the evolution of all D1 proteins (Cardona et al., 2015). Interestingly, there are a number of sequences that were very atypical and appeared to be early evolving. Because of their phylogenetic position and sequence characteristics, I suggested that it is possible that these D1 sequences evolved before the water oxidizing complex had reached its standard configuration in PSII.

Back then there were about 40-45 atypical sequences. Since them more have appeared, there are a total of 62 sequences... so here I show a Maximum Likelihood tree for all the atypical D1 forms. See Figure 1. Of particular interests is the fact that they seem to follow an evolutionary pattern consistent with vertical descent and loss, although some likely events of later gene transfer can also be identified.

Figure 1. Updated tree of atypical D1 sequences.

Of particular interest is the appearance of numerous D1 fragments. Some of them are from incompletely sequenced genes, but some of them seem to be legitimate proteins, probably originating from partial gene duplication followed by divergence (Figure 2). A couple of these fragmented D1 seems to have phylogenetic affinity for the early evolving forms.

Figure 2. Sequence alignments of different D1. That marked with Fr. is the D1 fragment, found in the genome of some of the earliest evolving cyanobacteria strains, Synechococcus sp. PCC 7336. It seems to have some affinity for the G0 and early branching forms.