Data from: Adaptive molecular evolution of a defence gene in sexual but not functionally asexual evening primroses

Theory predicts that sexual reproduction provides evolutionary advantages over asexual reproduction by reducing mutational load and increasing adaptive potential. Here, we test the latter prediction in the context of plant defences against pathogens because pathogens frequently reduce plant fitness and drive the evolution of plant defences. Specifically, we ask whether sexual evening primrose plant lineages (Onagraceae) have faster rates of adaptive molecular evolution and altered gene expression of a class I chitinase, a gene implicated in defence against pathogens, than functionally asexual evening primrose lineages. We found that the ratio of amino acid to silent substitutions (Ka/Ks = 0.19 vs. 0.11 for sexual and asexual lineages, respectively), the number of sites identified to be under positive selection (four vs. zero for sexual and asexual lineages, respectively) and the expression of chitinase were all higher in sexual than in asexual lineages. Our results are congruent with the conclusion that a loss of sexual recombination and segregation in the Onagraceae negatively affects adaptive structural and potentially regulatory evolution of a plant defence protein.理论预测，有性生殖相较于无性生殖可通过降低突变负荷、提升适应性潜力，从而赋予演化优势。本研究针对植物抵御病原体的场景验证了后者这一预测，原因在于病原体常会降低植物适合度，并驱动植物防御相关性状的演化。具体而言，本研究旨在探究：相较于功能性无性生殖的月见草谱系，有性生殖的月见草谱系（柳叶菜科，Onagraceae）是否具备更快的适应性分子演化速率，且I类几丁质酶（class I chitinase，一种参与病原体防御的基因）的基因表达是否存在差异。本研究发现：有性谱系与无性谱系的氨基酸替换与沉默替换速率比值（Ka/Ks，分别为0.19与0.11）、被鉴定为受正向选择的位点数量（有性谱系为4个，无性谱系为0个），以及几丁质酶的表达水平，在有性谱系中均显著高于无性谱系。本研究结果与如下结论一致：柳叶菜科物种中，有性重组与分离过程的丧失，会对植物防御蛋白的适应性结构演化及潜在的调控演化产生负面影响。