Key Lab of Molecular Biology of Crop Pathogens and Insects, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China; College of Plant Protection, Shanxi Agricultural University, Taigu, 030801, China.
Key Lab of Molecular Biology of Crop Pathogens and Insects, Institute of Biotechnology, Zhejiang University, Hangzhou, 310058, China; School of Agriculture and Food Sciences, Zhejiang Agriculture & Forestry University, Hangzhou, 311300, China.
Microbiol Res. 2021 Jul;248:126747. doi: 10.1016/j.micres.2021.126747. Epub 2021 Mar 16.
The host-selective ACT toxin is essential for the pathogenesis of the citrus fungal pathogen Alternaria alternata. However, the mechanism of ACT-toxin gene clusters ACT-toxin biosynthesis regulated by is still poorly understood. The biosynthesis of ACT toxin is mainly regulated by multiple ACT toxin genes located in the secondary metabolite gene cluster. In this study, we reported a transcription regulator ACTR contributes ACT toxin biosynthesis through mediating ACT toxin synthesis gene ACTS4 in Alternaria alternata. We generated ACTR-disrupted and -silenced mutants in the tangerine pathotype of A. alternata. Phenotype analysis showed that the ACTR mutants displayed a significant loss of ACT toxin production and a decreased virulence on citrus leaves whereas the vegetative growth and sporulation were not affected, indicating an essential role of ACTR in both ACT toxin biosynthesis and pathogenicity. To elucidate the transcription network of ACTR, we performed RNA-Seq experiments on wild-type and ACTR null mutant and identified genes that were differentially expressed between two genotypes. Transcriptome profiling and RT-qPCR analysis demonstrated that the ACT toxin biosynthetic gene ACTS4 is down-regulated in ACTR mutant. We generated ACTS4 knock-down mutant and found that the pathogenicity of ACTS4 mutant was severely impaired. Interestingly, both ACTR and ACTS4 are not involved in the response to different abiotic stresses including oxidative stress, salt stress, cell-wall disrupting regents, and metal ion stress, indicating the function of these two genes is highly specific. In conclusion, our results highlight the important regulatory role of ACTR in ACT toxin biosynthesis through mediating ACT toxin synthesis gene ACTS4 and underline the essential role of in the tangerine pathotype of A. alternata.
宿主专化性 ACT 毒素对于真菌病原菌Alternaria alternata 的致病过程至关重要。然而，ACT 毒素基因簇 ACT 毒素生物合成的调控机制仍知之甚少。ACT 毒素的生物合成主要受位于次级代谢基因簇中的多个 ACT 毒素基因调控。在本研究中，我们报道了转录调控因子 ACTR 通过介导 Alternaria alternata 中的 ACT 毒素合成基因 ACTS4 来促进 ACT 毒素的生物合成。我们在橘生型 A. alternata 中生成了 ACTR 敲除和沉默突变体。表型分析表明，ACTR 突变体的 ACT 毒素产量显著降低，对柑橘叶片的毒力降低，而营养生长和产孢不受影响，表明 ACTR 在 ACT 毒素生物合成和致病性方面都起着重要作用。为了阐明 ACTR 的转录调控网络，我们对野生型和 ACTR 缺失突变体进行了 RNA-Seq 实验，并鉴定了两种基因型之间差异表达的基因。转录组分析和 RT-qPCR 分析表明，ACT 毒素生物合成基因 ACTS4 在 ACTR 突变体中下调。我们生成了 ACTS4 敲低突变体，发现 ACTS4 突变体的致病性严重受损。有趣的是，ACTR 和 ACTS4 都不参与应对不同的非生物胁迫，包括氧化应激、盐胁迫、细胞壁破坏剂和金属离子胁迫，这表明这两个基因的功能具有高度特异性。综上所述，我们的研究结果强调了 ACTR 通过介导 ACT 毒素合成基因 ACTS4 在 ACT 毒素生物合成中的重要调控作用，并强调了其在橘生型 A. alternata 中的重要作用。
