Institute of Integrative Biology, Plant Pathology Group, ETH Zurich, Zurich, Switzerland.
PLoS One. 2009 Nov 18;4(11):e7884. doi: 10.1371/journal.pone.0007884.
Plant cell wall degrading enzymes (PCWDEs) of plant pathogens are receiving increasing interest for their potential to trigger plant defense reactions. In an antagonistic co-evolutionary arms race between host and pathogen, PCWDEs could be under strong selection. Here, we tested the hypothesis that PCWDEs in the fungal wheat pathogen Mycosphaerella graminicola have been positively selected by analyzing ratios of non-synonymous and synonymous nucleotide changes in the genes encoding these enzymes. Analyses of five PCWDEs demonstrated that one (beta-xylosidase) has been under strong positive selection and experienced an accelerated rate of evolution. In contrast, PCWDEs in the closest relatives of M. graminicola collected from wild grasses did not show evidence for selection or deviation from a molecular clock. Since the genealogical divergence of M. graminicola from these latter species coincided with the onset of agriculture, we hypothesize that the recent domestication of the host plant and/or agricultural practices triggered positive selection in beta-xylosidase and that this enzyme played a key role in the emergence of a host-specialized pathogen.
植物细胞壁降解酶（PCWDEs）是植物病原体的重要组成部分，因其能够触发植物防御反应而受到越来越多的关注。在宿主和病原体之间的拮抗协同进化军备竞赛中，PCWDE 可能受到强烈的选择压力。在这里，我们通过分析编码这些酶的基因中的非同义核苷酸和同义核苷酸变化的比值，来验证真菌小麦病原体禾谷球腔菌中的 PCWDEs 受到正向选择的假设。对五种 PCWDE 的分析表明，其中一种（β-木糖苷酶）受到强烈的正向选择，并经历了加速的进化速率。相比之下，从野生草中收集到的禾谷球腔菌最接近的亲缘种中的 PCWDE 没有表现出选择或偏离分子钟的证据。由于禾谷球腔菌与后一种物种的系统发育分歧与农业的开始相吻合，我们假设宿主植物的最近驯化和/或农业实践触发了β-木糖苷酶的正选择，并且该酶在宿主专化性病原体的出现中发挥了关键作用。
