Department of Plant-Microbe Interactions, Max Planck Institute for Plant Breeding Research, D-50829 Cologne, Germany.
Proc Natl Acad Sci U S A. 2013 Jun 11;110(24):E2219-28. doi: 10.1073/pnas.1306807110. Epub 2013 May 21.
Barley powdery mildew, Blumeria graminis f. sp. hordei (Bgh), is an obligate biotrophic ascomycete fungal pathogen that can grow and reproduce only on living cells of wild or domesticated barley (Hordeum sp.). Domestication and deployment of resistant barley cultivars by humans selected for amplification of Bgh isolates with different virulence combinations. We sequenced the genomes of two European Bgh isolates, A6 and K1, for comparative analysis with the reference genome of isolate DH14. This revealed a mosaic genome structure consisting of large isolate-specific DNA blocks with either high or low SNP densities. Some of the highly polymorphic blocks likely accumulated SNPs for over 10,000 years, well before the domestication of barley. These isolate-specific blocks of alternating monomorphic and polymorphic regions imply an exceptionally large standing genetic variation in the Bgh population and might be generated and maintained by rare outbreeding and frequent clonal reproduction. RNA-sequencing experiments with isolates A6 and K1 during four early stages of compatible and incompatible interactions on leaves of partially immunocompromised Arabidopsis mutants revealed a conserved Bgh transcriptional program during pathogenesis compared with the natural host barley despite ~200 million years of reproductive isolation of these hosts. Transcripts encoding candidate-secreted effector proteins are massively induced in successive waves. A specific decrease in candidate-secreted effector protein transcript abundance in the incompatible interaction follows extensive transcriptional reprogramming of the host transcriptome and coincides with the onset of localized host cell death, suggesting a host-inducible defense mechanism that targets fungal effector secretion or production.
大麦白粉病，布氏白粉菌 f. sp. hordei (Bgh)，是一种专性活体营养的子囊菌真菌病原体，只能在野生或驯化大麦（Hordeum sp.）的活细胞上生长和繁殖。人类通过驯化和部署抗性大麦品种，选择了具有不同毒力组合的 Bgh 分离株进行扩增。我们对来自欧洲的两个 Bgh 分离株 A6 和 K1 的基因组进行了测序，以便与参考基因组 DH14 进行比较分析。这揭示了一种镶嵌基因组结构，由具有高或低 SNP 密度的大型分离株特异性 DNA 块组成。一些高度多态性的块可能积累了超过 10000 年的 SNP，远在大麦驯化之前。这些分离株特异性的单态和多态交替区的块暗示了 Bgh 种群中存在异常大的遗传变异，可能是由罕见的异交和频繁的无性繁殖产生和维持的。在部分免疫缺陷拟南芥突变体叶片上进行的 A6 和 K1 分离株的 RNA-seq 实验，在与天然宿主大麦的相容和不相容互作的四个早期阶段，与致病性相关的 Bgh 转录程序具有保守性，尽管这些宿主之间存在约 2 亿年的生殖隔离。编码候选分泌效应蛋白的转录本大量诱导。在与宿主转录组的广泛重编程和局部宿主细胞死亡的开始相对应的，不相容互作中候选分泌效应蛋白转录本的丰度会特异性下降，这表明存在一种宿主诱导的防御机制，该机制靶向真菌效应物的分泌或产生。
