Rapid evolution in plant chitinases: Molecular targets of selection in plant-pathogen coevolution
Rapid evolution in plant chitinases: Molecular targets of selection in plant-pathogen coevolution
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DOI：
10.1073/pnas.97.10.5322
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发表时间：
2000-05-09
影响因子：
11.1
通讯作者：
Mitchell-Olds, T
中科院分区：
文献类型：
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作者：
Bishop, JG;Dean, AM;Mitchell-Olds, T
许多病原体识别基因，如植物R基因，经历了快速的适应性进化，提供了证据表明，这些基因在植物-病原体协同进化中起着关键作用。令人惊讶的是，快速适应性进化是否也发生在编码其他种类植物防御蛋白的基因中尚不清楚。与识别蛋白不同，植物几丁质酶直接攻击病原体，通过降解真菌细胞壁的一种成分几丁质来赋予抗病性。在这里，我们表明，非同义取代率在植物类I几丁质酶往往超过同义率在植物属阿拉伯芥（十字花科）和其他双子叶植物，表明一系列的自适应驱动的氨基酸替换。我们确定个别残基，可能受到积极的选择，通过使用密码子取代模型，并确定这些残基的位置上的三维结构的I类几丁质酶。与灵长类溶菌酶和植物III类几丁质酶相比，I类几丁质酶的结构和功能亲属，I类几丁质酶的适应性替换不成比例地发生在活性位点deft中。这种极不寻常的替换模式表明真菌通过酶抑制或其他形式的化学抗性直接防御几丁质分解活性，并确定了操纵几丁质分解活性的靶残基。这些数据也提供了经验证据，植物防御蛋白不参与病原体识别也演变的方式与快速共同进化的相互作用。
Many pathogen recognition genes, such as plant R-genes, undergo rapid adaptive evolution, providing evidence that these genes play a critical role in plant-pathogen coevolution. Surprisingly, whether rapid adaptive evolution also occurs in genes encoding other kinds of plant defense proteins is unknown. Unlike recognition proteins, plant chitinases attack pathogens directly, conferring disease resistance by degrading chitin, a component of fungal cell walls. Here, we show that nonsynonymous substitution rates in plant class I chitinase often exceed synonymous rates in the plant genus Arabis (Cruciferae) and in other dicots, indicating a succession of adaptively driven amino acid replacements. We identify individual residues that are likely subject to positive selection by using codon substitution models and determine the location of these residues on the three-dimensional structure of class I chitinase. In contrast to primate lysozymes and plant class III chitinases, structural and functional relatives of class I chitinase, the adaptive replacements of class I chitinase occur disproportionately in the active site deft This highly unusual pattern of replacements suggests that fungi directly defend against chitinolytic activity through enzymatic inhibition or other forms of chemical resistance and identifies target residues for manipulating chitinolytic activity. These data also provide empirical evidence that plant defense proteins not involved in pathogen recognition also evolve in a manner consistent with rapid coevolutionary interactions.