PDF(Pubmed)
Abstract：
Oomycete protists share phenotypic similarities with fungi, including the ability to cause plant diseases, but branch in a distant region of the tree of life. It has been suggested that multiple horizontal gene transfers (HGTs) from fungi-to-oomycetes contributed to the evolution of plant-pathogenic traits. These HGTs are predicted to include secreted proteins that degrade plant cell walls, a barrier to pathogen invasion and a rich source of carbohydrates. Using a combination of phylogenomics and functional assays, we investigate the diversification of a horizontally transferred xyloglucanase gene family in the model oomycete species Phytophthora sojae. Our analyses detect 11 xyloglucanase paralogs retained in P. sojae. Using heterologous expression in yeast, we show consistent evidence that eight of these paralogs have xyloglucanase function, including variants with distinct protein characteristics, such as a long-disordered C-terminal extension that can increase xyloglucanase activity. The functional variants analyzed subtend a phylogenetic node close to the fungi-to-oomycete transfer, suggesting the horizontally transferred gene was a bona fide xyloglucanase. Expression of three xyloglucanase paralogs in Nicotiana benthamiana triggers high-reactive oxygen species (ROS) generation, while others inhibit ROS responses to bacterial immunogens, demonstrating that the paralogs differentially stimulate pattern-triggered immunity. Mass spectrometry of detectable enzymatic products demonstrates that some paralogs catalyze the production of variant breakdown profiles, suggesting that secretion of variant xyloglucanases increases efficiency of xyloglucan breakdown as well as diversifying the damage-associated molecular patterns released. We suggest that this pattern of neofunctionalization and the variant host responses represent an aspect of the Red Queen host-pathogen coevolutionary dynamic.
摘要：
卵菌原生生物与真菌的表型相似，包括引起植物病害的能力，而是在生命之树的遥远区域的分支。有人认为，从真菌到卵菌的多个水平基因转移（HGT）有助于植物致病性状的进化。预计这些HGTs包括降解植物细胞壁的分泌蛋白，病原体入侵的屏障和丰富的碳水化合物来源。使用系统基因组学和功能测定的组合，我们研究了卵菌模型物种疫霉中水平转移的木葡聚糖酶基因家族的多样性。我们的分析检测到保留在P.sojae中的11个木葡聚糖酶旁系同源物。利用在酵母中的异源表达，我们显示了一致的证据，其中八个旁系同源物具有木葡聚糖酶功能，包括具有独特蛋白质特征的变体，例如可以增加木葡聚糖酶活性的长无序C端延伸。分析的功能变异指向一个接近真菌到卵菌转移的系统发育节点，表明水平转移的基因是真正的木葡聚糖酶。烟草中三种木葡聚糖酶旁系同源物的表达触发了高活性氧（ROS）的产生，而其他人抑制ROS对细菌免疫原的反应，证明旁系同源物不同地刺激模式触发的免疫。可检测的酶产物的质谱表明，一些旁系同源物催化变体分解谱的产生，这表明分泌变异的木葡聚糖酶增加了木葡聚糖分解的效率，并使释放的损伤相关分子模式多样化。我们建议这种新功能化模式和变异宿主反应代表了RedQueen宿主-病原体共进化动态的一个方面。
