Biomedical Engineering Reference
In-Depth Information
and race 2) and
V. albo-atrum
have been sequenced (Klosterman et al. 2011,
Maruthachalam et al. 2011b). Based on comparative genomics of these three
Verticillium
strains, several novel genes and potential virulence determinants
have been identifi ed (Klosterman et al. 2011, Maruthachalam et al. 2011b).
This information would be invaluable for functional characterization
of many important genes in these pathogens. Both forward and reverse
genetic approaches via ATMT provide a unique opportunity to create the
genetic mutations in a manner that facilitates subsequent isolation and
characterization of mutated genes.
Magnaporthe oryzae
(anamorph:
Pyricularia oryzae
) is a fi lamentous,
heterothallic, ascomycetous fungus and a causal agent of rice blast disease,
the most serious disease of cultivated rice. Each year enough rice to feed
60 million people is destroyed by this disease (Zeigler et al. 1995). Since
rice is a staple food and accounts for a signifi cant proportion of caloric and
protein intake in many countries (
http://www.irri.org/
),
the disease is one
of the major threats to food security worldwide (Talbot 2003). Indeed, the
Center for Disease Control and Prevention listed rice blast as a signifi cant
biological weapon.
Magnaporthe oryzae
, like many foliar plant pathogens, is highly adapted
to penetrate and subsequently colonize its host (Dean 1997). Once the
conidia land on the surface of the host leaf, they germinate along the surface.
Upon the recognition of environmental cues such as surface hydrophobicity
(Lee and Dean 1994), specialized infection structures called appressoria
begin to develop. Once appressorium forms, turgor pressure of up to 8
Mpa is accumulated within the appressorium. Using the turgor pressure,
the fungus ruptures the plant cuticle layer and gains access to the tissues
that serve as the reservoir of the nutrients. Next, it establishes a parasitic
relationship with and derives the nutrients from host cells to grow within
the plant. This may ultimately lead to the death of the host plant
(Fig. 2).
Genome sequence of
M. oryzae
was also released and made public (Dean
et al. 2005). Unlike the most plant-fungal pathogen system, genome of its
host plant, rice was sequenced as well, providing a model system for the
study of interactions between the pathogen and its host simultaneously.
Over the past two decades, several genes required for infection-specifi c
morphogenesis and pathogenicity have been identified in
M. oryzae
,
based on the gene expression analysis and forward and reverse genetic
approaches (Dean 1997, Talbot 2003, Sesma and Osburn 2004, Kankanala
et al. 2007, Jeon et al. 2007). First, ATMT method was described for this
fungus as an effi cient insertional mutagenesis technique (Rho et al. 2001)
and subsequently several groups employed this method and developed
mutants in large-scale (Jeon et al. 2007, Zhou et al. 2009, Meng et al. 2007).
Among these, Jeon et al. (2007) generated a library of 21,070 transformants
