Laboratory of Molecular and Cellular Biology, All-Russia Research Institute for Agricultural Microbiology (ARRIAM), Podbelsky chaussee 3, St. Petersburg, Russia, 196608.
Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, pr. Torez 44, St. Petersburg, Russia, 194223.
Protoplasma. 2019 Sep;256(5):1449-1453. doi: 10.1007/s00709-019-01383-1. Epub 2019 Apr 25.
Pisum sativum symbiotic mutant SGEFix-2 carries the sym33-3 allele of the gene Sym33, encoding transcription factor PsCYCLOPS/PsIPD3. Previously, strong host cell defence reactions were identified in nodules of this mutant. In the present study, new manifestations of defence reactions were revealed in 28-day-old white nodules in which bacterial release had occurred. These nodules were investigated using histochemical staining of pectin and suberin and by immunogold localisation of three components of pectin: highly methyl-esterified homogalacturonan (HG) recognised by monoclonal antibody JIM7, low methyl-esterified HG recognised by JIM5 and linear (1-4)-β-D-galactan side-chain of rhamnogalacturonan I (RG I) recognised by LM5. In the mutant, but not in the wild-type, cell wall material was deposited around the vacuole in the uninfected cells, in cells containing infection threads and in the infected cells. The deposits around the vacuole were marked with JIM7 and LM5 antibodies but not with JIM5, suggesting that they contain newly formed cell wall material. Deposition was accompanied by suberin accumulation. This is the first report that deposition of cell wall material around the vacuole may be associated with the defence reaction in ineffective nodules. In addition, hypertrophic infection droplets labelled with JIM7 were identified. In the matrix of some infection threads, RG I recognised a pectic gel component. Callose deposits in the cell walls and in the walls of infection threads were occasionally observed. The observations suggest that an important function of transcriptional factor CYCLOPS/IPD3 is the suppression of defence reactions during establishment of the legume-rhizobial symbiosis.
豌豆共生突变体 SGEFix-2 携带基因 Sym33 的 sym33-3 等位基因，该基因编码转录因子 PsCYCLOPS/PsIPD3。此前，在该突变体的根瘤中发现了强烈的宿主细胞防御反应。在本研究中，在已发生细菌释放的 28 天龄白色根瘤中，揭示了新的防御反应表现。使用果胶和栓质的组织化学染色以及果胶的三个成分的免疫胶体金定位（高度甲酯化的同半乳糖醛酸聚糖（HG）被单克隆抗体 JIM7 识别，低甲酯化的 HG 被 JIM5 识别，以及鼠李半乳糖醛酸聚糖 I（RG I）的线性（1-4）-β-D-半乳糖侧链被 LM5 识别）研究了这些根瘤。在突变体中，但不在野生型中，细胞壁物质在未感染细胞、含有感染线的细胞和感染细胞中的液泡周围沉积。围绕液泡的沉积物被 JIM7 和 LM5 抗体标记，但不被 JIM5 标记，表明它们含有新形成的细胞壁物质。沉积伴随着栓质的积累。这是第一个关于液泡周围细胞壁物质沉积可能与无效根瘤防御反应相关的报告。此外，还鉴定了用 JIM7 标记的肥大感染液滴。在一些感染线的基质中，识别出 RG I 果胶凝胶成分。在细胞壁和感染线的细胞壁中偶尔观察到胼胝质沉积。这些观察表明，转录因子 CYCLOPS/IPD3 的一个重要功能是在豆科植物-根瘤菌共生体建立过程中抑制防御反应。
