Biomedical Engineering Reference
In-Depth Information
Hormonal Signals
The ability of
Trichoderma
spp. to promote plant growth led to the
investigations on whether these fungi produce phytohormones and that
the growth promotion is due only to the better nutrient uptake or also
is a cumulative effect of hormone-like molecules production. Recently, it
has been demonstrated that wild-type Arabidopsis seedlings inoculated
with either
T. virens
or
T. atroviride
showed characteristic auxin-related
phenotypes, including increased biomass production and stimulated
lateral root development (Contreras-Cornejo et al. 2009). When grown
under axenic conditions,
T. virens
produced the auxin-related compounds
indole-3-acetic acid, indole-3-acetaldehyde and indole-3-ethanol.
Mutations in genes involved in auxin transport or signaling,
AUX1
,
BIG
,
EIR1
and
AXR1
, were found to reduce the growth-promoting and root
developmental effects of
T. virens
inoculation. RNAi silencing of the ACCD
(1-aminocyclopropane-1-carboxylate deaminase) gene in
T. asperellum
showed decreased ability of the mutants to promote root elongation of
canola seedlings. These data suggest a role for ACCD in the plant root
growth-promotion effect by
T. asperellum
(Viterbo et al. 2010).
Endopolygalacturonase
In a significant finding, a plant cell wall degrading enzyme
(endopolygalacturonase) was found to be involved in root colonization
by
T. harzianum
(Moran-Diez et al. 2009). Using a proteome analysis and
a three-component (
Trichoderma
—tomato plantlets-pathogen) system,
this enzyme was identifi ed to be upregulated during plant interactions.
Compared with the wild-type strain,
Thpg1
-silenced transformants
showed lower PG activity, less growth on pectin medium and reduced
capability to colonize tomato roots. These results were combined with
microarray comparative data from the transcriptome of Arabidopsis
plants inoculated with the wild type or a
Thpg1
-silenced transformant
(ePG5). The endoPG-encoding gene was found to be required for active
root colonization and plant defense induction by
T.
harzianum
T34.
Elicitors
One of the earliest proteins from
Trichoderma
to act as an inducer of
resistance is the
T. viride
endoxylanase encoded by
xyn2
gene
.
This
protein induces ethylene formation in tobacco and
tomato (Dean and
Anderson, 1991). However, the catalytic activity of this enzyme is not
required for elicitation of plant defense (Enkerli et al., 1999, Sharon et al.,
