State Key Laboratory of Crop Stress Biology in Arid Areas, Shaanxi Key Laboratory of Agricultural and Environmental Microbiology, College of Life Sciences, Northwest A&F University, Yangling, 712100, China.
College of Medical Technology, Shaanxi University of Chinese Medicine, Xianyang, 712046, China.
Planta. 2019 Dec;250(6):1897-1910. doi: 10.1007/s00425-019-03267-3. Epub 2019 Sep 4.
A homologue of the ribosomal protein L22e, Rpf84, regulates root nodule symbiosis by mediating the infection process of rhizobia and preventing bacteroids from degradation in Robinia pseudoacacia. Ribosomal proteins (RPs) are known to have extraribosomal functions, including developmental regulation and stress responses; however, the effects of RPs on symbiotic nodulation of legumes are still unclear. Ribosomal protein 22 of the large 60S subunit (RPL22), a non-typical RP that is only found in eukaryotes, has been shown to function as a tumour suppressor in animals. Here, a homologue of RPL22, Rpf84, was identified from the leguminous tree R. pseudoacacia. Subcellular localization assays showed that Rpf84 was expressed in the cytoplasm and nucleus. Knockdown of Rpf84 by RNA interference (RNAi) technology impaired the infection process and nodule development. Compared with the control, root and stem length, dry weight and nodule number per plant were drastically decreased in Rpf84-RNAi plants. The numbers of root hair curlings, infection threads and nodule primordia were also significantly reduced. Ultrastructure analyses showed that Rpf84-RNAi nodules contained fewer infected cells with fewer bacteria. In particular, remarkable deformation of bacteroids and fusion of multiple symbiosomes occurred in infected cells. By contrast, overexpression of Rpf84 promoted nodulation, and the overexpression nodules maintained a larger infection/differentiation region and had more infected cells filled with bacteroids than the control at 45 days post inoculation, suggesting a retarded ageing process in nodules. These results indicate for the first time that RP regulates the symbiotic nodulation of legumes and that RPL22 may function in initiating the invasion of rhizobia and preventing bacteroids from degradation in R. pseudoacacia.
核糖体蛋白 L22e 的同源物 Rpf84 通过调节根瘤菌的侵染过程并防止类菌体降解来调控刺槐共生结瘤。核糖体蛋白（RPs）已知具有核糖体外功能，包括发育调控和应激反应；然而，RPs 对豆科植物共生结瘤的影响尚不清楚。核糖体蛋白 22 大亚基（RPL22）是一种非典型的核糖体蛋白，仅在真核生物中发现，已被证明在动物中作为肿瘤抑制因子发挥作用。在这里，从豆科刺槐中鉴定出 RPL22 的同源物 Rpf84。亚细胞定位实验表明，Rpf84 在细胞质和细胞核中表达。通过 RNA 干扰（RNAi）技术敲低 Rpf84 会损害侵染过程和根瘤发育。与对照相比，Rpf84-RNAi 植株的根和茎长、干重和每株植物的根瘤数明显减少。根毛卷曲、侵染线和根瘤原基的数量也显著减少。超微结构分析表明，Rpf84-RNAi 根瘤中含有较少的感染细胞和较少的细菌。特别是，感染细胞中的类菌体变形和多个共生体融合明显。相比之下，Rpf84 的过表达促进了结瘤，而过表达根瘤在接种后 45 天保持较大的侵染/分化区，并且含有更多充满类菌体的感染细胞，表明根瘤的衰老过程减缓。这些结果首次表明，RP 调节豆科植物的共生结瘤，并且 RPL22 可能在启动根瘤菌的侵染和防止刺槐中类菌体降解方面发挥作用。
