Ren Jing, Wang Qi, Zhang Xiaxia, Cao Yongheng, Wu JingXia, Tian Juan, Yu Yanjun, Gong Qingqiu, Kong Zhaosheng
State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China.
University of Chinese Academy of Sciences, Beijing, 100049, China.
Adv Sci (Weinh). 2025 Apr;12(15):e2414519. doi: 10.1002/advs.202414519. Epub 2025 Feb 22.
Legumes establish symbiosis with rhizobia by forming a symbiotic interface that enables cross-kingdom exchanges of signaling molecules and nutrients. However, how host organelles interact with symbiosomes at the symbiotic interface remains elusive during rhizobia endosymbiosis. Here, symbiotic cells are reconstructed using 3D scanning electron microscopy (SEM) and uncover that the host endoplasmic reticulum (ER) undergoes dynamic expansion to gradually enwrap symbiosomes, facilitating their compartmentalization and endosymbiosis. Consistently, altering ER lamellar expansion by overexpressing MtRTNLBs, the reticulons responsible for ER tubulation, impairs rhizobia accommodation and symbiosome development. Intriguingly, unfolded protein response (UPR)-marker genes, bZIP60 and IRE1A/B, show continuously activated expression during nodule development, and the two UPR-deficient mutants, ire1b, and bzip60, exhibit compromised ER biogenesis and defective symbiosome development. Collectively, the findings underpin ER expansion and UPR activation as two key events in rhizobia accommodation and reveal an intrinsic coupling of ER morphology with proper UPR during root nodule symbiosis.
豆科植物通过形成共生界面与根瘤菌建立共生关系，该共生界面能够实现信号分子和营养物质的跨界交换。然而，在根瘤菌内共生过程中，宿主细胞器如何在共生界面与共生体相互作用仍不清楚。在此，利用三维扫描电子显微镜（SEM）重建共生细胞，发现宿主内质网（ER）经历动态扩张，逐渐包裹共生体，促进其区室化和内共生。一致地，通过过表达MtRTNLBs（负责内质网管状化的网织蛋白）来改变内质网片层扩张，会损害根瘤菌的容纳和共生体发育。有趣的是，未折叠蛋白反应（UPR）标记基因bZIP60和IRE1A/B在根瘤发育过程中显示持续激活表达，并且两个UPR缺陷突变体ire1b和bzip60表现出内质网生物合成受损和共生体发育缺陷。总的来说，这些发现支持内质网扩张和UPR激活是根瘤菌容纳中的两个关键事件，并揭示了根瘤共生过程中内质网形态与适当UPR的内在耦合。
