Clues to an Evolutionary Mystery: The Genes for T-Toxin, Enabler of the Devastating 1970 Southern Corn Leaf Blight Epidemic, Are Present in Ancestral Species, Suggesting an Ancient Origin
Clues to an Evolutionary Mystery: The Genes for T-Toxin, Enabler of the Devastating 1970 Southern Corn Leaf Blight Epidemic, Are Present in Ancestral Species, Suggesting an Ancient Origin
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DOI：
10.1094/mpmi-03-18-0070-r
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发表时间：
2018-11-01
影响因子：
3.5
通讯作者：
Turgeon, B. Gillian
中科院分区：
文献类型：
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作者：
Condon, Bradford J.;Elliott, Candace;Turgeon, B. Gillian
1970年南方玉米叶枯病（SCLB）的流行摧毁了整个美国东部单一栽培的t细胞质玉米田。这种流行病是由T种驱动的，这是一种以前未见过的异养蜗种。巧合的是，另一种真菌毛条菌（Phyllosticta zeae-maydis）也具有同样的生物学特异性。T小种产生T毒素，而玉米毛条虫产生PMtoxin，两者都是宿主选择性聚酮毒素，是产生超毒力所必需的。目前丰富的基因组序列为解决t和pm毒素生物合成基因的进化起源提供了一个机会，以前认为这些基因是这些物种独有的。利用C. heterostrophus基因作为探针，我们在另外6种Dothideomycete和3种Eurotiomycete中鉴定出了同源基因。与基因片段化的种族T Tox1基因座编码这些基因形成鲜明对比的是，其他物种中所有新发现的Tox1样基因都位于一个共线基因座上。这种紧凑的排列、系统发育分析、弓形虫蛋白树拓扑结构与物种树的比较以及弓形虫基因特征表明，该位点是古老的，包括C. heterostrophus在内的一些物种通过水平基因转移获得了弓形虫。异养棘球绦虫和玉米毛条绦虫在SCLB流行时没有交换Tox1 DNA，但它们如何获得Tox1仍不清楚。虽然在C. heterostrophus和Phyllosticta zeae-maydis中没有，但在其他物种的tox1样簇中存在额外的基因，这表明产生的代谢物与t和pm毒素不同。
The Southern corn leaf blight (SCLB) epidemic of 1970 devastated fields of T-cytoplasm corn planted in monoculture throughout the eastern United States. The epidemic was driven by race T, a previously unseen race of Cochliobolus heterostrophus. A second fungus, Phyllosticta zeae-maydis, with the same biological specificity, appeared coincidentally. Race T produces T-toxin, while Phyllosticta zeae-maydis produces PMtoxin, both host-selective polyketide toxins necessary for supervirulence. The present abundance of genome sequences offers an opportunity to tackle the evolutionary origins of T-and PM-toxin biosynthetic genes, previously thought unique to these species. Using the C. heterostrophus genes as probes, we identified orthologs in six additional Dothideomycete and three Eurotiomycete species. In stark contrast to the genetically fragmented race T Tox1 locus that encodes these genes, all newly found Tox1-like genes in other species reside at a single collinear locus. This compact arrangement, phylogenetic analyses, comparisons of Tox1 protein tree topology to a species tree, and Tox1 gene characteristics suggest that the locus is ancient and that some species, including C. heterostrophus, gained Tox1 by horizontal gene transfer. C. heterostrophus and Phyllosticta zeae-maydis did not exchange Tox1 DNA at the time of the SCLB epidemic, but how they acquired Tox1 remains uncertain. The presence of additional genes in Tox1-like clusters of other species, although not in C. heterostrophus and Phyllosticta zeae-maydis, suggests that the metabolites produced differ from T-and PM-toxin.