InnB, a Novel Type III Effector of Bradyrhizobium elkanii USDA61, Controls Symbiosis With Vigna Species
InnB, a Novel Type III Effector of Bradyrhizobium elkanii USDA61, Controls Symbiosis With Vigna Species
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DOI：
10.3389/fmicb.2018.03155
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发表时间：
2018-12-18
影响因子：
5.2
通讯作者：
Okazaki, Shin
中科院分区：
文献类型：
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作者：
Nguyen, Hien P.;Ratu, Safirah T. N.;Okazaki, Shin
埃氏慢生根瘤菌USDA 61与绿豆（Vigna radiata cv. KPS 1）和大豆（Glycine max cv. BARC 2），不能使任何一种植物生长。这种不相容性是由于存在功能性III型分泌系统（T3 SS），其将效应蛋白易位到宿主细胞中。我们先前在B中鉴定了五个基因。elkanii，负责其与KPS 1植物不相容。其中，一个新的基因命名为innB表现出与T3 SS相关的一些特征，并被发现负责限制KPS 1的表达。在本研究中，我们通过分析基因表达、蛋白分泌和共生表型进一步表征了innB。innB基因被发现编码一个假设的蛋白质，这是高度保守的T3 SS-窝藏根瘤菌。与其他根瘤菌T3 SS相关基因相似，innB的表达依赖于植物类黄酮和转录调节因子Ttsl。InnB蛋白通过T3 SS分泌，并且对于其他促凝外部蛋白的分泌不是必需的。此外，通过腺苷酸环化酶测定证实了InnB进入结节细胞的T3 SS依赖性易位。根据接种试验，使用几个豇豆品种，InnB促进至少一个V mungo品种的成熟。这些结果表明，innB编码一种新的III型效应控制与豇豆物种的共生。
Bradyrhizobium elkanii USDA61 is incompatible with mung bean (Vigna radiata cv. KPS1) and soybean (Glycine max cv. BARC2) and unable to nodulate either plant. This incompatibility is due to the presence of a functional type III secretion system (T3SS) that translocates effector protein into host cells. We previously identified five genes in B. elkanii that are responsible for its incompatibility with KPS1 plants. Among them, a novel gene designated as innB exhibited some characteristics associated with the T3SS and was found to be responsible for the restriction of nodulation on KPS1. In the present study, we further characterized innB by analysis of gene expression, protein secretion, and symbiotic phenotypes. The innB gene was found to encode a hypothetical protein that is highly conserved among T3SS-harboring rhizobia. Similar to other rhizobial T3SS-associated genes, the expression of innB was dependent on plant flavonoids and a transcriptional regulator Ttsl. The InnB protein was secreted via the T3SS and was not essential for secretion of other nodulation outer proteins. In addition, T3SS-dependent translocation of InnB into nodule cells was confirmed by an adenylate cyclase assay. According to inoculation tests using several Vigna species, InnB promoted nodulation of at least one V mungo cultivar. These results indicate that innB encodes a novel type III effector controlling symbiosis with Vigna species.