Department of Plant Pathology, University of Arkansas, Fayetteville, AR 72701, USA.
Fungal Genet Biol. 2010 Dec;47(12):973-80. doi: 10.1016/j.fgb.2010.08.003. Epub 2010 Aug 16.
Rice blast disease is the single most destructive plant disease that threatens stable rice production worldwide. Race-specific resistance to the rice blast pathogen has not been durable and the mechanism by which the resistance is overcome remains largely unknown. Here we report the molecular mechanisms of diversification and the instability of the avirulence gene AVR-Pita1 in field strains of Magnaporthe oryzae interacting with the host resistance gene Pi-ta and triggering race-specific resistance. Two-base-pair insertions resulting in frame-shift mutations and partial and complete deletions of AVR-Pita1 were identified in virulent isolates. Moreover, a total of 38 AVR-Pita1 haplotypes encoding 27 AVR-Pita1 variants were identified among 151 avirulent isolates. Most DNA sequence variation was found to occur in the exon region resulting in amino acid substitution. These findings demonstrate that AVR-Pita1 is under positive selection and mutations of AVR-Pita1 are responsible for defeating race-specific resistance in nature.
稻瘟病是全球范围内威胁稳定水稻生产的最具破坏性的植物病害之一。针对稻瘟病菌的特定抗性并不持久，而抗性被克服的机制在很大程度上仍不清楚。在这里，我们报告了与宿主抗性基因 Pi-ta 相互作用并引发特定抗性的稻瘟病菌 avirulence 基因 AVR-Pita1 的多样化和不稳定性的分子机制。在毒力分离株中鉴定出导致移码突变和 AVR-Pita1 的部分和完全缺失的两个碱基对插入。此外，在 151 个无毒分离株中鉴定出了总共编码 27 个 AVR-Pita1 变体的 38 个 AVR-Pita1 单倍型。大多数 DNA 序列变异发生在外显子区域，导致氨基酸取代。这些发现表明 AVR-Pita1 受到正选择，AVR-Pita1 的突变是导致自然中特定抗性被克服的原因。
