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Figure 6.7 Alignment of five cyanobacterial TrHb1-2s (top) and four TrHb1-1s (bottom)
using Nostoc punctiforme TrHb1-2 as the query. The top line indicates secondary struc-
ture as found in Synechococcus sp. strain PCC 7002 GlbN (PDB ID 4I0V). Residues in bold
are at positions B10, E10, F8 and H16, as numbered by structural homology to the
canonical 3/3 fold. The proteins and organisms are: B2IV60_NOSP7 Nostoc punctiforme
strain ATCC 29133/PCC 73102; D8G8J5_9CYAN Oscillatoria sp. PCC 6506;
K9VF25_9CYAN Oscillatoria nigro-viridis PCC 7112; K9WZP6_9NOST Cylindrospermum
stagnale PCC 7417; K9UL54_9CHRO Chamaesiphon minutus PCC 6605; B4VMT4_9CYAN
Coleofasciculus chthonoplastes PCC 7420; K9XN27_9CHRO Gloeocapsa sp. PCC 7428;
B2J6Y7_NOSP7 N. punctiforme strain ATCC 29133/PCC 73102; Q8RT58_SYNP2 Syn-
echococcus sp. strain PCC 7002.
into doubt according to the phylogenetic analysis of these photosynthetic-
truncated globins. It is remarkable that the intron structure of the eukaryotic
globin genes has proved practically useless for the purpose of understanding
these events (
Vinogradov, Fernandez, et al., 2011
). As more genetic informa-
tion becomes available and a more diverse group of genomic sequences is
incorporated into phylogenetic analyses, it will be fascinating to learn if globins
and their evolution can be used to shed light on the development of
eukaryotic photosynthesis.
Thus within the primary endosymbionts, there is a single lineage for the
3/3 Hbs, arguing that from a canonical Hb perspective, the Archaeplastida
are in fact monophyletic. Since this is at odds with the heterogeneity seen in
the phylogenetic data for the TrHbs, it is now proposed that the origin of the
canonical Hbs is from a horizontal gene transfer resulting from the original
mitochondrial endosymbiotic event, probably involving a precursor of a
present-day proteobacteria (
Vinogradov, Fernandez, et al., 2011
). The over-
all picture therefore becomes one where, in the case of photosynthetic
eukaryotes, the canonical 3/3 Hbs were acquired first as the result of
