Fungal effectors play critical roles in manipulating plant immune responses and promoting colonization. Sphaerulina musiva is a heterothallic ascomycete fungus that causes Septoria leaf spot and stem canker disease in Populus plantations. This disease can result in premature defoliation, branch and stem breakage, increased mortality, and plantation failure. However, little is known about the interaction between S. musiva and Populus. Previous work predicted 142 candidate secreted effector proteins in S. musiva (SmCSEPs), 19 of which were selected for further functional characterization in this study. SmCSEP3 induced plant cell death in Nicotiana benthamiana, while 8 out of 19 tested SmCSEPs suppressed cell death. The signal peptides of these eight SmCSEPs exhibited secretory activity in a yeast signal sequence trap assay. Confocal microscopy revealed that four of these eight SmCSEPs target both the cytoplasm and the nucleus, whereas four predominantly localize to discrete punctate structures. Pathogen challenge assays in N. benthamiana demonstrated that the transient expression of six SmCSEPs promoted Fusarium proliferatum infection. The expression of these six SmCSEP genes were induced during infection. SmCSEP2, SmCSEP13, and SmCSEP25 suppressed chitin-triggered reactive oxygen species burst and callose deposition in N. benthamiana. The candidate secreted effector proteins of S. musiva target multiple compartments in the plant cell and modulate different PTI pathways.

中文翻译：

---

杨树叶斑病和茎溃疡病病原体 Sphaerulina musiva 的分泌效应蛋白以多种方式操纵植物免疫并增强毒力。

真菌效应子在操纵植物免疫反应和促进定植方面发挥着关键作用。Sphaerulina musiva 是一种异宗体子囊菌真菌，可在杨树种植园中引起壳针孢叶斑病和茎溃疡病。这种疾病会导致过早落叶、枝条和茎折断、死亡率增加和种植失败。然而，人们对 S. musiva 和杨树之间的相互作用知之甚少。先前的工作预测了 S. musiva (SmCSEP) 中的 142 个候选分泌效应蛋白，其中 19 个被选择用于本研究中的进一步功能表征。SmCSEP3 诱导本塞姆氏烟草植物细胞死亡，而 19 个测试的 SmCSEP 中有 8 个抑制细胞死亡。这八个 SmCSEP 的信号肽在酵母信号序列捕获测定中表现出分泌活性。共聚焦显微镜显示，这八个 SmCSEP 中的四个同时靶向细胞质和细胞核，而四个主要定位于离散的点状结构。本塞姆氏烟草中的病原体攻击测定表明，六种 SmCSEP 的瞬时表达促进了增殖镰刀菌感染。这六个 SmCSEP 基因的表达在感染过程中被诱导。SmCSEP2、SmCSEP13 和 SmCSEP25 抑制本塞姆氏烟草中几丁质触发的活性氧爆发和胼胝质沉积。S. musiva 的候选分泌效应蛋白靶向植物细胞中的多个区室并调节不同的 PTI 途径。