Ophiobolus heterostrophus

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Cochliobolus heterostrophus
Ophiobolus heterostrophus (Drechsler, 1925)
Cochliobolus heterostrophus (Drechsler, 1934)
Anamorphs Helminthosporium maydis (Nisikado
Miyake, 1926) Bipolaris maydis (Shoemaker,
1959) Drechslera maydis (Subramanian P.C.
Jain,1966)
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The Southern Corn Leaf Blight Epidemic
1970s
-- the worst plant disease epidemic on record
More than 30 states affected 15 corn crop
destroyed gt1 billion lost
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Cochliobolus heterostrophus
two races
race T
race O
Texas male sterile (T)-cytoplasm corn
1970 Designation of race T (Smith et al Hooker
et al)
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Race T produces a host selective toxin, T-toxin
1971 Discovery of T-toxin in culture filtrates
(Lim Hooker Gracen et al)
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One of the worlds three most important cereal
crops
The host Corn
40 of the world corn crop is produced in the
United States
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THE PRODUCTION OF HYBRID SEEDS USING
NORMAL PARENT
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Emasculation of Corn
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T-cytoplasm corn, Cytoplasmic Male Sterility and
T-toxin Sensitivity
T-corn corn with Texas male sterile
cytoplasm (T-cms, or T-cytoplasm)
T-urf13- a hybrid gene consisting of parts of
2 mitochondrial genes and one chloroplast gene
URF13- a 13 kD protein (mitochondrial inner
membrane)
(modified from Wise et al, 1999)
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ENVIRONMENT favorable weather
C. heterostrophus (the rise of race T)
Southern Corn Leaf Blight (1970)
T-cytoplasm corn (genetic homogeneity)
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T-URF-13, Expressed in E. coli, Confers
Sensitivity to T-toxin
race O
race T
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Genetic Analysis of Tox1
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Tox1 a single genetic locus
(Yoder and Gracen, 1975)
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Reciprocal translocation
612
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Race O Chromosomes
Race T Chromosomes
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Generation of race T mutants deficient in
ability to produce T-toxin
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Crosses
Single locus Tox1
Tox1 mutants X race O or race T (race T
background)
Two loci, Tox1A and Tox1B
(G. Yang M. Rose)
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Tox1 is two loci physical evidence






(Kodama et al, 1999)
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Tentative Model for Evolution of Race T from
Race O
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Identification of Tox1 genes
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Identification of Tox1 genes
Tox1A

• PKS1 polyketide synthase

Tox1B

• DEC1 decarboxylase
• RED1 medium chain reductase/dehydrogenase

(G. Yang M. Rose)
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Assay of tox1- mutants on T-cms corn
race T
race O
pks1-
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Tox1 genes are unique to race T
C. heterostrophus race O
C. heterostrophus race T
C. carbonum
C. victoriae
C. sativus
C. spicifer
Probe
?
PKS1
9.4-
23.1-
DEC1
RED1
2.3-
Ge Yang Mark Rose
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Identification of Tox1 genes by genome sequence
analysis
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Shotgun Approach to Sequencing the Cochliobolus
Genome
35 Mb
genomic DNA
Torrey Mesa Research Institute/Syngenta
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Identification of Tox1 genes by Genome Sequence
Analysis

• Query of the C. heterostrophus genome sequence
  database with four known Tox1 genes (PKS1, PKS2,
  DEC1, and RED1)

• These genes mapped to three scaffolds
• 4FP (carrying PKS1)
• 4LU (carrying PKS2)
• 3PL (carrying DEC1 and RED1)

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C. heterostrophus Scaffold 4FP
23,099 kb
contig 1
contig 2
contig 5
contig 4
contig 3
23,099
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PKS1
Scaffold 4FP is at Tox1A
PKS1 polyketide synthase
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Functional analysis of new Tox1 genes
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Organization of Genes for T-toxin Biosynthesis at
Tox1
C. heterostrophus
LAM1
A T rich
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Are there additional PKSs at Tox1 ?

• 25 PKSs in C. heterostrophus, including PKS1 and
  PKS2

• Screen for PKSs that are only in race T to find
  PKSs at Tox1

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Presence ()/Absence (-) in race T and race O