Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
Center for Nano Materials and Technology (CNMT), Japan Advanced Institute of Science and Technology (JAIST), Ishikawa, Japan.
J Biol Chem. 2021 Dec;297(6):101370. doi: 10.1016/j.jbc.2021.101370. Epub 2021 Oct 29.
Fungal plant pathogens secrete virulence-related proteins, called effectors, to establish host infection; however, the details are not fully understood yet. Functional screening of effector candidates using Agrobacterium-mediated transient expression assay in Nicotiana benthamiana identified two virulence-related effectors, named SIB1 and SIB2 (Suppression of Immunity in N. benthamiana), of an anthracnose fungus Colletotrichum orbiculare, which infects both cucurbits and N. benthamiana. The Agrobacterium-mediated transient expression of SIB1 or SIB2 increased the susceptibility of N. benthamiana to C. orbiculare, which suggested these effectors can suppress immune responses in N. benthamiana. The presence of SIB1 and SIB2 homologs was found to be limited to the genus Colletotrichum. SIB1 suppressed both (i) the generation of reactive oxygen species triggered by two different pathogen-associated molecular patterns, chitin and flg22, and (ii) the cell death response triggered by the Phytophthora infestans INF1 elicitin in N. benthamiana. We determined the NMR-based structure of SIB1 to obtain its structural insights. The three-dimensional structure of SIB1 comprises five β-strands, each containing three disulfide bonds. The overall conformation was found to be a cylindrical shape, such as the well-known antiparallel β-barrel structure. However, the β-strands were found to display a unique topology, one pair of these β-strands formed a parallel β-sheet. These results suggest that the effector SIB1 present in Colletotrichum fungi has unique structural features and can suppress pathogen-associated molecular pattern-triggered immunity in N. benthamiana.
真菌植物病原体分泌毒力相关蛋白，称为效应子，以建立宿主感染；然而，细节尚未完全了解。使用农杆菌介导的瞬时表达测定法在本氏烟中对效应子候选物进行功能筛选，鉴定出炭疽病真菌胶孢炭疽菌的两个与毒力相关的效应子，命名为 SIB1 和 SIB2（抑制本氏烟中的免疫），它们感染葫芦科植物和本氏烟。SIB1 或 SIB2 的农杆菌介导的瞬时表达增加了本氏烟对 C. orbiculare 的易感性，这表明这些效应子可以抑制本氏烟中的免疫反应。发现 SIB1 和 SIB2 同源物仅存在于胶孢炭疽菌属中。SIB1 抑制了两种不同的病原体相关分子模式（几丁质和 flg22）触发的活性氧的产生，以及由 Phytophthora infestans INF1 激发素在本氏烟中触发的细胞死亡反应。我们确定了基于 NMR 的 SIB1 结构，以获得其结构见解。SIB1 的三维结构由五个β-链组成，每个β-链包含三个二硫键。发现整体构象为圆柱形，类似于众所周知的反平行β-桶结构。然而，β-链被发现具有独特的拓扑结构，其中一对β-链形成平行的β-片层。这些结果表明，存在于胶孢炭疽菌中的效应子 SIB1 具有独特的结构特征，可以抑制本氏烟中病原体相关分子模式触发的免疫。
