Transcriptome Analysis of Poplar during Leaf Spot Infection with Sphaerulina spp.

Diseases of poplar caused by the native fungal pathogen Sphaerulina musiva and related species are of growing concern, particularly with the increasing interest in intensive poplar plantations to meet growing energy demands. Sphaerulina musiva is able to cause infection on leaves, resulting in defoliation and canker formation on stems. To gain a greater understanding of the different responses of poplar species to infection caused by the naturally co-evolved Sphaerulina species, RNA-seq was conducted on leaves of Populus deltoides, P. balsamifera and P. tremuloides infected with S. musiva, S. populicola and a new undescribed species, Ston1, respectively. The experiment was designed to contain the pathogen in a laboratory environment, while replicating disease development in commercial plantations. Following inoculation, trees were monitored for disease symptoms, pathogen growth and host responses. Genes involved in phenylpropanoid, terpenoid and flavonoid biosynthesis were generally upregulated in P. balsamifera and P. tremuloides, while cell wall modification appears to play an important role in the defense of P. deltoides. Poplar defensive genes were expressed early in P. balsamifera and P. tremuloides, but their expression was delayed in P. deltoides, which correlated with the rate of disease symptoms development. Also, severe infection in P. balsamifera led to leaf abscission. This data gives an insight into the large differences in timing and expression of genes between poplar species being attacked by their associated Sphaerulina pathogen.

由本土真菌病原菌杨生球座菌（Sphaerulina musiva）及该属近缘物种引发的杨树病害正日益受到学界关注，尤其在当前为满足日益增长的能源需求，集约化杨树人工林培育热度持续攀升的背景下。杨生球座菌可侵染杨树叶片引发落叶，并在茎干部位形成溃疡病斑。为深入解析不同杨树物种对自然共演化的球座菌属（Sphaerulina）病原菌侵染的响应差异，研究团队分别对受Sphaerulina musiva、杨生球座菌（Sphaerulina populicola）及一株暂未定名的新物种Ston1侵染的美洲杨（Populus deltoides）、香脂杨（Populus balsamifera）和颤杨（Populus tremuloides）的叶片开展了RNA测序（RNA-seq）实验。本实验将病原菌控制在实验室环境内，同时模拟商业人工林中的病害发展进程。接种后，研究人员对植株的病害症状、病原菌生长情况及宿主应答反应进行了监测。参与苯丙烷类、萜类及黄酮类生物合成的基因在香脂杨与颤杨中普遍上调表达，而细胞壁修饰似乎在美洲杨的防御过程中发挥关键作用。香脂杨与颤杨的杨树防御基因表达启动较早，而美洲杨的防御基因表达则出现延迟，这与病害症状的发展速率呈现显著相关性。此外，香脂杨遭受严重侵染后会引发叶片脱落。本数据集为解析受关联球座菌属病原菌侵染的不同杨树物种在基因表达时序与表达模式上的显著差异提供了重要研究视角。