Table_2_The nuclear-encoded plastid ribosomal protein L18s are essential for plant development.XLSX

Plastid ribosomal proteins (PRPs) are necessary components for plastid ribosome biogenesis, playing essential roles in plastid development. The ribosomal protein L18 involved in the assemble of 5S rRNA and 23S rRNA, is vital for E. coli viability, but the functions of its homologs in plant plastid remain elusive. Here, we characterized the functions of the plant plastid ribosomal protein L18s (PRPL18s) in Arabidopsis and rice. AtPRPL18 was ubiquitously expressed in most of the plant tissues, but with higher expression levels in seedling shoots, leaves, and flowers. AtPRPL18 was localized in chloroplast. Genetic and cytological analyses revealed that a loss of function of AtPRPL18 resulted in embryo development arrest at globular stage. However, overexpression of AtPRPL18 did not show any visible phenotypical changes in Arabidopsis. The rice OsPRPL18 was localized in chloroplast. In contrast to AtPRPL18, knockout of OsPRPL18 did not affect embryo development, but led to an albino lethal phenotype at the seedling stage. Cytological analyses showed that chloroplast development was impaired in the osprpl18-1 mutant. Moreover, a loss-function of OsPRPL18 led to defects in plastid ribosome biogenesis and a serious reduction in the efficiency of plastid intron splicing. In all, these results suggested that PRPL18s play critical roles in plastid ribosome biogenesis, plastid intron splicing, and chloroplast development, and are essential for plant survival.

质体核糖体蛋白（Plastid ribosomal proteins, PRPs）是质体核糖体生物发生的必需组分，在质体发育中发挥关键作用。参与5S核糖体RNA（5S rRNA）与23S核糖体RNA（23S rRNA）组装的核糖体蛋白L18，对大肠杆菌（E. coli）的存活至关重要，但其在植物质体中的同源蛋白功能仍不明确。本研究对拟南芥和水稻中的植物质体核糖体蛋白L18（PRPL18s）的功能进行了系统表征。AtPRPL18在植物绝大多数组织中呈广谱表达，且在幼苗地上部分、叶片及花中表达水平相对更高。AtPRPL18定位于叶绿体。遗传与细胞学分析显示，AtPRPL18功能缺失会导致拟南芥胚胎发育停滞于球形胚阶段；而过表达AtPRPL18并未使拟南芥产生可见表型变化。水稻OsPRPL18同样定位于叶绿体。与AtPRPL18不同，敲除OsPRPL18不会影响水稻胚胎发育，但会导致植株在幼苗期出现白化致死表型。细胞学分析表明，osprpl18-1突变体的叶绿体发育存在缺陷。此外，OsPRPL18功能缺失会引发质体核糖体生物发生缺陷，并显著降低质体内含子剪接效率。综上，本研究结果表明，PRPL18s在质体核糖体生物发生、质体内含子剪接与叶绿体发育中发挥关键作用，且是植物存活所必需的。