Annual Report 2006

Taxonomic analysis of
species, as the causal pathogens
of soybean sudden death
syndrome and dry bean root-rot
The etiological agents of soybean sudden
death syndrome (SDS) have been reported as
or its forma specialis, f. sp. On
the other hand, the causal pathogens of dry
bean or mung bean root-rot have been known
as f. sp. Soybean SDS
pathogens isolated from the US, Argentina and
Brazil, dry bean root-rot pathogens from the US
and Japan, and mung bean root-rot pathogen
from Canada were investigated. Detailed
phenotypic comparisons of macro- and
microscopic features, and phylogenetic analyses
of multilocus DNA sequence data indicated that
the soybean SDS and dry bean root-rot
pathogens comprised six morphologically and
phylogenetically distinct species (Fig. 5).
Soybean SDS in North and South America (US,
Argentina and Brazil) was found to be caused
by four species:
and an undescribed
species of By way of contrast, dry or
mung bean root-rot in North America (US and
Canada) and Japan is caused by two closely
related species, and
The SDS species do not form an exclusive
group within the molecular phylogeny, indicating
they may not have a monophyletic origin.
Artificial inoculation tests on a susceptible
variety of soybean, using the isolates from
soybeans, dry beans and mung beans, revealed
that all six species can induce typical SDS
symptoms on the inoculated soybean plants.
Genome-wide gene expression
analysis of
pv.
To survey genes regulated by HrpG or
HrpX, we constructed a DNA macroarray
system consisting of 2,384 of genomic DNA
fragments of strain T7174 (MAFF311018) of
It comprised about 95.5% of the whole
genome DNA. Using this macroarray system, it
was confirmed that the gene cluster (about
87k to 120k region of the Xoo genome) was up
regulated in wild type strain under inducing
medium, while it was not up regulated
in the ∆ and ∆ mutants (Fig. 6).
Moreover, it was revealed that thirteen
genomic regions were regulated by HrpG or
HrpX. To check that expression of genes within
these regions were really controlled by the
HrpG or HrpX, a real-time quantitative RT-PCR
system was used. Finally, six genes (XOO0037,
XOO0078, XOO1388, XOO2263, XOO4042 and
XOO4134) were newly identified. In addition,
Fig. 5
Four soybean SDS pathogens (A-C, F) and two
dry bean root-rot pathogens (D, E)
A:
B:
C:
D:
E:
F: (undescribed species).
Fig. 6
Schematic representation of regions with up- and down
-regulated gene expression in inducing condition
( / wild type strain)