Biology Reference
In-Depth Information
proteins is grouped in cluster I, being encoded by
opxA
. A second protein
is comprised in cluster II, being codified by
opxB
. Finally, Cyan7822_0909
forms a cluster with a bootstrap value of 100% with alr2294 from
Nostoc
sp.
7120. This unexpected phylogenetic proximity is likely the result of HGT.
Interestingly, in what concerns the unicellular cyanobacteria, only the
opxA
and
opxB
of
Cyanothece
sp. PCC 7822 and
Microcystis
are located in the
vicinity of
pcp
homologues although the PCP encoded by the genes close
to
opxB
do not possess the typical Interpro domains of other bacterial PCP
proteins, which prevented its identification.
3.1.2.2. Filamentous cyanobacteria
Most of the filamentous strains possess more than two
opx
homologues.
The phylogenetic relationship observed for the OPX from cluster 7 is
supported by a high bootstrap value. In addition, the genes encoding
these proteins are contiguous to
pcp
orthologues, whose encoded proteins
are also consistently grouped in the PCP tree (
Fig. 7.5
A, cluster 2). This
strongly suggests that the cluster 7 OPX proteins are the outcome of the
ancestor
opxA
and that, later on, two paralogous duplications occurred in
the lineage that give rise to
Lyngbya
and
Arthrospira
spp., and in the last
common ancestral organism of
Microcoleus
and
Oscillatoria
. Another parsi-
monious hypothesis should also be considered. Indeed, it is possible that
the
opxA
gene underwent two paralogous duplications in the last common
ancestor of the filamentous strains and, after speciation,
Trichodesmium
lost
two of its paralogues. Although this last hypothesis is plausible, the distribu-
tion pattern of the OPX in the phylogenetic tree, with the orthologues of
Arthrospira
spp. being grouped separately from the ones belonging to
Micro-
coleus
and
Oscillatoria
strongly support the first scenario. The two additional
OPX present in
Lyngbya
were probably acquired by HGT from other cya-
nobacteria, or result from an HGT followed by a paralogous duplication.
Finally, for
M. chthonoplastes
, it is likely that
opxA
underwent a duplica-
tion event giving rise to the sequences grouped in cluster 2, whereas the
MC7420_5658 was probably acquired by HGT. All of these events gave
rise to the large number of homologues from filamentous cyanobacteria
that are comprised in cluster I. Regarding the cluster II, the
opxB
encod-
ing the proteins comprised in clusters 10 and 11 are in the vicinity of
genes putatively related to LPS biosynthesis. Nevertheless, similar to what
was observed previously, these proteins do not possess the typical Interpro
domains of other bacterial PCP proteins, and therefore, were not consid-
ered in this study.
