The plasma membrane (PM)-localized receptor-like kinases (RLKs) play important roles in pathogen defense. One of the first cloned RLKs is the Arabidopsis receptor kinase FLAGELLIN SENSING 2 (FLS2), which specifically recognizes a conserved 22 amino acid N-terminal sequence of Pseudomonas syringae pv．tomato DC3000 (Pst) flagellin protein (flg22). Although extensively studied in Arabidopsis, the functions of RLKs in crop plants remain largely uninvestigated. To understand the roles of RLKs in soybean (Glycine max), GmFLS2 was silenced via virus induced gene silencing (VIGS) mediated by Bean pod mottle virus (BPMV). No significant morphological differences were observed between GmFLS2-silenced plants and the vector control plants. However, silencing GmFLS2 significantly enhanced the susceptibility of the soybean plants to Pseudomonas syringae pv．glycinea (Psg). Kinase activity assay showed that silencing GmFLS2 significantly reduced the phosphorylation level of GmMPK6 in response to flg22 treatment. However, reduced phosphorylation level of both GmMPK3 and GmMPK6 in response to Psg infection was observed in GmFLS2-silenced plants, implying that defense response is likely transduced through activation of the downstream GmMAPK signaling pathway upon recognition of bacterial pathogen by GmFLS2. The core peptides of flg22 from Pst and Psg were highly conserved and only 4 amino acid differences were seen at their N-termini. Interestingly, it appeared that the Psg-flg22 was more effective in activating soybean MAPKs than activating Arabidopsis MAPKs, and conversely, Pst-flg22 was more effective in activating Arabidopsis MAPKs than activating soybean MAPKs, suggesting that the cognate recognition is more potent than heterologous recognition in activating downstream signaling. Taken together, our results suggest that the function of FLS2 is conserved in immunity against bacteria pathogens across different plant species.

中文翻译：

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沉默 GmFLS2 通过减弱 GmMAPK 信号通路的激活增强大豆对细菌病原体的敏感性

质膜 (PM) 定位的受体样激酶 (RLK) 在病原体防御中发挥重要作用。最早克隆的 RLK 之一是拟南芥受体激酶 FLAGELLIN SENSING 2 (FLS2)，它特异性识别丁香假单胞菌 pv．tomato DC3000 (Pst) 鞭毛蛋白 (flg22) 的保守的 22 个氨基酸 N 端序列。尽管在拟南芥中进行了广泛的研究，但 RLK 在作物植物中的功能在很大程度上仍未得到研究。为了了解 RLK 在大豆（Glycine max）中的作用，GmFLS2 通过由豆荚斑驳病毒 (BPMV) 介导的病毒诱导基因沉默 (VIGS) 进行沉默。在 GmFLS2 沉默的植物和载体对照植物之间没有观察到显着的形态差异。然而，沉默 GmFLS2 显着增强了大豆植物对 Pseudomonas syringae pv．glycinea (Psg) 的易感性。激酶活性测定表明沉默 GmFLS2 显着降低了响应 flg22 处理的 GmMPK6 的磷酸化水平。然而，在 GmFLS2 沉默的植物中观察到 GmMPK3 和 GmMPK6 响应 Psg 感染的磷酸化水平降低，这意味着防御反应可能通过 GmFLS2 识别细菌病原体后激活下游 GmMAPK 信号通路来转导。来自 Pst 和 Psg 的 flg22 的核心肽是高度保守的，在它们的 N 端仅观察到 4 个氨基酸差异。有趣的是，似乎 Psg-flg22 在激活大豆 MAPKs 方面比激活拟南芥 MAPKs 更有效，相反，Pst-flg22 在激活拟南芥 MAPKs 方面比激活大豆 MAPKs 更有效，表明同源识别在激活下游信号传导方面比异源识别更有效。总之，我们的结果表明 FLS2 的功能在针对不同植物物种的细菌病原体的免疫中是保守的。