Trichoderma Genes Involved in Interactions with Fungi and Plants - Biotechnology of Fungal Genes - page 151

Trichoderma spp. to be known as “opportunistic avirulent symbionts”
(Harman et al. 2004, Shoresh et al. 2010). The benefi ts of such interactions
range from improved nutrients uptake to imparting immunity in plants
to pathogens are driven by a nutritional relationships where Trichoderma
use plant sucrose and in return enhance photosynthetic ability of plants
(Vargas et al. 2008, 2009). Trichoderma spp. are also known for their
ability to reduce oxidative damage to plants/seeds and negates effects
of seed aging (Harman et al. 2006, Shoresh and Harman 2008, Matsouri
et al. 2010). By virtue of improving root growth, these fungi also impart
drought tolerance, in addition to improving plant nutrition (Altomare et al.
1999). Some strains are reported to produce phytohormones (like auxins)
that help improving the plant biomass (Contreras-Cornejo et al. 2009).
Trichoderma spp. also produce a large number of secondary metabolites
that infl uence interactions with plants and other microbes. The advent of
molecular genetics has improved our knowledge of details of interactions
of Trichoderma with plants and other fungi. The purpose of this review
is to highlight the mechanisms of such interactions at the genetic level.
INTERACTIONS WITH OTHER FUNGI
Trichoderma spp. are capable of parasitizing other fungi and derive
nutrients from these hosts (Brotman et al. 2010). This property of these
fungi to destroy other fungi has been the driving force behind the
commercial success of Trichoderma spp. as biofungicides. In a typical case
of mycoparasitism, the fi rst step is the sensing/recognition of the host
fungi, which is followed by attachment of the mycoparasite to the host
hyphae and often, but not always, coiling around. The mycoparasite then
produce a range of hydrolytic enzymes to solubilize the host fungi, thus
deriving nutrients. Trichoderma spp. are not only capable of degrading the
hyphae of many plant pathogenic fungi, they also can readily colonize
and degrade the resting structures like the sclerotia of Sclerotium rolfsii ,
Rhizoctonia solani and Sclerotinia spp. This is of utmost importance in
biocontrol as these pathogenic fungi survive in soil in the form of resting
structures that initiate infection once the crop is sown.
Hydrolytic Enzymes
Among the hydrolytic enzymes deployed by Trichoderma spp. to parasitize
other fungi are several chitinases, glucanases, cellulases, proteases and
recently studied laccases (Viterbo et al. 2002b). Disruption of ech42 in T.
harzianum did not affect disease control ability against S. rolfsii and R. solani
(Carsolio et al.1999). In the contrary, Woo et al. (1999) disrupted ech42 in
T. harzianum P1 ( T. atroviride ) and showed reduced biocontrol activity