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3.1.1.3. Heterocystous cyanobacteria
In general, the pcp homologues from heterocystous cyanobacteria are
grouped within clusters supported by high bootstrap values, similar to that
observed for 16S rRNA sequences ( Brito et al., 2012 ). As previously men-
tioned, two duplication events are predicted to have occurred in the last
common ancestor of the heterocystous strains, giving rise to the paralogues
putatively involved in cell division (cluster 9) or in the synthesis of the poly-
saccharidic layer of heterocysts (cluster 10). Interestingly, Anabaena variabilis
ATCC 29413 appears to have lost its pcp orthologue from cluster 9. A pcp
orthologue from the obligate symbiont Nostoc azollae 0708 is also miss-
ing from cluster 11. The loss of this orthologue may be related with its
symbiotic competence. Nevertheless, one additional PCP sequence of this
strain and one belonging to C. raciborskii CS-505 are grouped in a cluster
separated from other heterocystous sequences (cluster 6), most likely result-
ing from the acquisition of a pcp by their common ancestor through HGT.
A paralogous duplication is also expected to have occurred in the ancestor
of A. variabilis ATCC 29413 and Nostoc PCC 7120 (cluster 13). In addi-
tion, this ancestor also acquired two pcp sequences by HGT, giving raise to
the sequences grouped in clusters 15 and 16. After the branching of these
organisms, a paralogous duplication gave rise to the A. variabilis sequence
in cluster 14, whereas Nostoc acquired another homologue by HGT (clus-
ter 7). Regarding N. punctiforme PCC 73102, four duplications are postu-
lated, given that all of these paralogues cluster together with sequences from
heterocystous cyanobacteria. A different pattern is observed for Nodularia
spumigina CCY 9414, where two HGT events gave rise to the homologue
from cluster 7 (the sequences encoding N9414_07896 and N9414_07903
are in different genomic contigs, but are most likely part of the same gene)
and that of cluster 16. It is interesting to observe that this cluster comprises
sequences that resulted from two separate events of HGT in heterocystous
strains, namely, in the ancestor of A. variabilis and N. punctiforme and in
Nodularia . Given the strong phylogenetic relationship usually observed for
heterocystous strains, it is possible that these particular sequences play an
important physiological role in these strains.
3.1.2. Reconstruction of the OPX evolutionary history
in cyanobacteria
The OPX proteins are characterized by the presence of a PES domain
(IPR003715). The analysis performed revealed that this motif is common
in cyanobacteria, with most of the strains possessing at least one putative
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