Biomedical Engineering Reference
In-Depth Information
copious amounts of gliotoxin within 16 hours of growth in liquid culture
(Wilhite and Straney 1996) and the compound can be detected in the
rhizosphere (Lumsden et al. 1992). There are contradictory reports on
the role of gliotoxin in biocontrol under controlled conditions (Howell et
al. 1993, Wilhite et al. 1994, Howell and Stipanovic 1995, Howell 2006).
The “P” strains, on the other hand, produce the fungistatic compound
gliovirin that has been suggested to be involved in biocontrol of
Pythium
spp. (Howell et al. 2003).
T. virens
produces the fungistatic and anti-
cancer steroidal compound viridin (Howell et al. 1993), which can also
be reduced to viridiol that has herbicidal properties (Jones and Hancock
1987). Mukherjee et al. (1996) identifi ed a
T. virens
gene cluster that
includes the terpene cyclase VIR4 and cytochrome P450s, however, the
role of this cluster in secondary metabolism remains to be ascertained. The
adenylate cyclase gene
tac1
has recently been demonstrated to regulate the
biosynthesis of viridin/viridiol (Mukerjee et al. 2007).
T. brevicompactum
produces trichodermin, a terpenoid trichothecene type toxin that is highly
fungitoxic and phytotoxic and formed by the trichodiene synthase TRI5
(Tijerino et al. 2011). The biosynthesis of α-pentyl-pyrone, a volatile
component (“coconut aroma”) with antifungal activity formed by some
Trichoderma
spp. is one of the best studied secondary metabolites from a
biocontrol perspective (Bonnarme et al. 1997, Cooney et al. 1997, Reithner
et al. 2005, 2007, Vinale et al. 2009). Rubio et al. (2009) demonstrated the
involvement of the transcription factor Thctf1 in 6-PP production by
T.
harzianum
.
Signaling Genes
Compared to
Neurospora
,
Aspergillus
and
Magnaporthe
, studies on the role
of cell signaling mechanisms in
Trichoderma
have not been exhaustive
(Zeilinger and Omann 2007). Since eukaryotic signaling mechanisms
are well conserved, it is interesting to examine the role of the signaling
elements in mycoparasitism, antibiosis and biocontrol. The two species
that have been studied for the role of signaling in growth, development
and antagonism are
T. atroviride
and
T. virens
. Antisense-mediated
silencing of Tga1 (G
α
) resulted in reduced cAMP level in
T. atroviride
IMI 206040 (Rocha-Ramirez et al. 2002). The loss-of-function mutants
showed light-independent hyper-sporulation and reduced mycoparasitic
coiling. On the other hand, transgenic strains carrying multi-copies of the
gene overgrew
R. solani
colonies at a faster rate. Interestingly, the same
Tga1, when deleted in
T. atroviride
ATCC 78058, resulted in elevated
internal cAMP level (Reithner et al. 2005). The knockout mutants showed
continuous sporulation in a light-independent manner and a total loss
of mycoparasitic overgrowth and lysis of the host fungi. These mutants
