Biology Reference
In-Depth Information
a PCP protein in this organism is most certainly the result from the lost
of its ancestor orthologue during the contraction of its genome. Regard-
ing
Microcystis aeruginosa
NIES-843, the significant sequence similarity of
one of its sequences with PCP belonging to filamentous and heterocystous
strains (cluster 14) suggests that its encoded gene was acquired by HGT. A
similar origin is also predicted for the gene encoding the Cyan7822_5718
in
Cyanothece
sp. PCC 7822, which is phylogenetically distant from other
cyanobacterial PCP. In this organism, a paralogous duplication is predicted
to have originated the third PCP protein.
3.1.1.2. Filamentous cyanobacteria
All the filamentous strains analysed possess one or more PCP protein.
Cluster 2, which is supported by a high bootstrap value (97%), com-
prises one orthologue from each of these strains, with the exception of
Microcoleus chthonoplastes
PCC 7420. The genomic context of the genes
encoding these proteins is relatively conserved, indicating a common ori-
gin (
Guerrero et al., 2005
). The absence of an orthologue from
Microco-
leus
is not surprising as this organism branched early within this group,
being distantly related from the other filamentous strains. After its separa-
tion from the other strains, four duplications within its genome lead to
the five paralogues identified. A few other paralogous duplications can
be postulated for the filamentous strains: two occurring in the common
ancestor of
Microcoleus vaginatus
FGP-2 and
Oscilatoria
PCC 6506 (clusters
1 and 4), another occurring in the lineage that gave rise to
Arthrospira
maxima
CS-328,
Arthrospira platensis
NIES-39, and
Lyngbya
PCC 8106
(cluster 3), and three occurring in this last organism after its separation
from the
Arthrospira
spp. ancestor (sequences comprised in clusters 1 and 4
and L8106_15385). The presence of L8106_09871, AmaxDRAFT_2895
and NIES39_C04940 in cluster II, along with sequences from hetero-
cystous cyanobacteria, strongly suggests an HGT event occurring in
the last common ancestor of these three filamentous strains. Indeed, the
genomic regions containing the genes encoding AmaxDRAFT_2895 and
NIES39_C04940 are very similar, supporting the hypothesis of a common
origin for these genes in these strains. In addition, although the synteny
does not extend to
Lyngbya
, L8106_09871 is phylogenetically close to the
Arthrospira
spp. orthologues, suggesting a reshuffle of this gene within
Lyn-
gbya
's genome. An additional HGT event, occurring after the branching of
this strain can account for the gene encoding the L8106_27951, grouped
with heterocystous sequences in cluster I.
