Biology Reference
In-Depth Information
ROS produced by the host.
B. cinerea
has a single FHb-coding gene,
Bcfhg1
(
Turrion-Gomez, Eslava, & Benito, 2010
). Its expression is developmentally
regulated, with maximum levels during germination of conidia. Expression
is enhanced on exposure to NO and expression
in planta
parallels the expres-
sion pattern during saprophytic growth with maximal expression occurring
during the very early stages of the infection process.
Bcfhg1
complemented
the
S. cerevisiae yhb1
mutation, indicating that the encoded FHb has
NO-consuming activity. Studies with
Bcfhg1
deletion mutants suggest that,
although BCFHG1 confers protection against NO, the ability of the mutant
strains to infect different hosts was not affected.
Aspergillus oryzae
(Supplementary Table S2 at
http://www.elsevier
direct.com/companions/9780124076938
) is an asexual, ascomycetous
fungus used for hundreds of years in the production of soy sauce,
miso and sake. There are conflicting opinions about whether
A. oryzae
can be isolated in nature.
A. oryzae
and
A. flavus
are so closely related that
all strains of the former are regarded by some as natural variants of
A. flavus
modified through years of selection for fermenting of foods.
A. oryzae
is
regarded as not being pathogenic for plants or animals, though there are a
handful of reports of isolation of this fungus from patients. The protective
function of FHb has been shown in
A. oryzae
(
Zhou et al., 2009
) and, more
recently, two FHbs were found in
A. oryzae
and
A. niger
(Eurotiomycetes)
FHb1 (416/417 residues) and FHb2 (436/439 residues); the N-terminus of
the latter contains a potential signal sequence. Furthermore, FHb1 is mono-
meric, occurs in the cytosol and uses either NADH or NADPH as electron
donor, while FHb2 is dimeric, is located in mitochondria, and can use only
NADH (
Zhou et al., 2011
). Interestingly, only the expression of the cyto-
solic FHb1 is up-regulated in the presence of NO. It was also suggested
that the reductases of the two FHbs tend to promote oxidative damage
(
Zhou et al., 2010
).
Te Biesebeke et al. (2010)
have shown that the
A
.
oryzae
FHb1 transcription levels appear to be positively correlated with hyphal
growth. Moreover, not all the N-terminal extensions have predicted mito-
chondrial transit peptides as observed for
A
.
nidulans
,
A. terreus
,
A. fumigatus
and
A. oryzae
(
Te Biesebeke et al., 2010
), but rather have predicted signal
peptides suggesting that localization of the FHbs is species dependent. It
should be mentioned that many Ascomycetes have two or more FHbs
(
Hoogewijs, Dewilde, et al., 2012
). Deletion of the FHb gene
fhbA
of
A
.
nidulans
induces sexual development and decreases sterigmatocystin
(a mycotoxin
related
to
aflatoxins)
production
(
Baidya, Cary,
Grayburn, & Calvo, 2011
).
