Agriculture Reference
In-Depth Information
Figure 6. QS regulatory cascades in
R. leguminosarum
bv.
viciae
strain A34. Strain A34 has four well
characterized QS systems. The
cinRI
system is chromosomal and responsible for the production of 3-
hydroxy-C
14:1
-HSL, which acts as a master inductor of the
tra, rhi
and
rai
systems, each of which has
also its own autoinducing loop. The
tra
and
rhi
systems are localized to the symbiotic plasmid pRL1JI,
together with genes that determine inhibition of growth under the regulation of 3-hydroxy-C
14:1
-HSL.
tra-trb
genes are responsible for the conjugal transfer of pRL1JI, while the
Rhi proteins play a role in
nodulation.
raiRI
are localized to a megaplasmid (pIJ9001) and the genes regulated by this QS-system
remain unknown. The BisR protein plays a double role, as it controls
traR
expression and hence
induction of the
tra-trb
genes, but at the same time represses the expression of
cinI
, both in response to
3-hydroxy-C
14:1
-HSL. Repression of
cinI
by BisR keeps low levels of 3-hydroxy-C
14:1
-HSL production
in strains already carrying pRL1JI (potential donors). Strains not carrying the pRL1JI plasmid (potential
recipients) overproduce 3-hydroxy-C
14:1
-HSL, which is detected by the pRL1JI-carrying strains, hereby
inducing the expression of
tra-trb
genes and transfer of the plasmid to the recipient cells. See text for
further details. The figure is based on data gathered from Cubo
et al.
, 1992, Rodelas
et al.
, 1999,
Lithgow
et al.
, 2000, Wilkinson
et al.
, 2002, Wisniewski-Dyé
et al.
, 2002, Danino
et al.
, 2003.
Strain A34 carries a fourth QS-system (
raiIR
) under the control of 3-hydroxy-C
14:1
-HSL,
in a non-symbiotic megaplasmid [Wisniewsky-Dyé
et al.
, 2002]. Mutation of these genes
does not show any effect on nodulation or symbiotic nitrogen fixation [Wisniewsky-Dyé
et
al.
, 2002].
raiIR
are absent from most analyzed
R. leguminosarum
bv.
viciae
strains
[Sánchez-Contreras
et al.
, 2007] and its potentially regulated phenotypes are unknown
[Wisniewski-Dyé
et al.
, 2002].
In brief, the quorum sensing regulatory cascade topped by the
cinRI
system in
R.
leguminosarum
bv.
viciae
strain A34 has been shown related to the regulation of expression
of the
rhi
genes and conjugative plasmid transfer, and appears to influence a variety of
phenotypes including nodulation, expression of genes for adaptation to stress, entry into
