Six New Genes Required for Production of T-Toxin, a Polyketide Determinant of High Virulence of <i>Cochliobolus heterostrophus</i> to Maize
Bibliographic record
Abstract
Southern Corn Leaf Blight, one of the worst plant disease epidemics in modern history, was caused by Cochliobolus heterostrophus race T, which produces T-toxin, a determinant of high virulence to maize carrying Texas male sterile cytoplasm. The genetics of T-toxin production is complex and the evolutionary origin of associated genes is uncertain. It is known that ability to produce T-toxin requires three genes encoded at two unlinked loci, Tox1A and Tox1B, which map to the breakpoints of a reciprocal translocation. DNA associated with Tox1A and Tox1B sums to about 1.2 Mb of A+T rich, repeated DNA that is not found in less virulent race O or other Cochliobolus species. Here, we describe identification and targeted deletion of six additional genes, three mapping to Tox1A and three to Tox1B. Mutant screens indicate that all six genes are involved in T-toxin production and high virulence to maize. The nine known Tox1 genes encode two polyketide synthases (PKS), one decarboxylase, five dehydrogenases, and one unknown protein. Only two have a similar phylogenetic profile. To trace evolutionary history of one of the core PKS, DNA from more than 100 Dothideomycete species were screened for homologs. An ortholog (60% identity) was confirmed in Didymella zeae-maydis, which produces PM-toxin, a polyketide of similar structure and biological specificity as T-toxin. Only one additional Dothideomycete species, the dung ascomycete Delitschia winteri harbored a paralog. The unresolved evolutionary history and distinctive gene signature of the PKS (fast-evolving, discontinuous taxonomic distribution) leaves open the question of lateral or vertical transmission.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".