Ribosome assembly factors guide the complex process by which ribosomal proteins and the ribosomal RNAs form a functional ribosome. However, the assembly of plant plastid ribosomes is poorly understood. In the present study, we discovered a maize (Zea mays) plastid ribosome assembly factor based on our characterization of the embryo defective 15 (emb15) mutant. Loss of function of Emb15 retards embryo development at an early stage, but does not substantially affect the endosperm, and causes an albino phenotype in other genetic backgrounds. EMB15 localizes to plastids and possesses a ribosome maturation factor M (RimM) domain in the N‐terminus and a predicted UDP‐GlcNAc pyrophosphorylase domain in the C‐terminus. The EMB15 RimM domain originated in bacteria and the UDP‐GlcNAc pyrophosphorylase domain originated in fungi; these two domains came together in the ancestor of land plants during evolution. The N‐terminus of EMB15 complemented the growth defect of an Escherichia coli strain with a RimM deletion and rescued the albino phenotype of emb15 homozygous mutants. The RimM domain mediates the interaction between EMB15 and the plastid ribosomal protein PRPS19. Plastid 16S rRNA maturation is also significantly impaired in emb15. These observations suggest that EMB15 functions in maize seed development as a plastid ribosome assembly factor, and the C‐terminal domain is not important under normal conditions.

中文翻译：

---

Emb15 编码对玉米胚胎发生必不可少的质体核糖体组装因子

核糖体组装因子指导核糖体蛋白和核糖体 RNA 形成功能性核糖体的复杂过程。然而，人们对植物质体核糖体的组装知之甚少。在本研究中，我们根据我们对胚胎缺陷 15 ( emb15 ) 突变体的表征发现了一种玉米 ( Zea mays ) 质体核糖体组装因子。Emb15功能丧失在早期阶段阻碍胚胎发育，但基本上不影响胚乳，并在其他遗传背景下导致白化表型。EMB15 定位于质体并在 N 端具有核糖体成熟因子 M (RimM) 结构域，在 C 端具有预测的 UDP-GlcNAc 焦磷酸化酶结构域。EMB15 RimM 域起源于细菌，UDP-GlcNAc 焦磷酸化酶域起源于真菌；这两个域在进化过程中在陆地植物的祖先中聚集在一起。EMB15的N-末端的补充的生长缺陷的大肠杆菌用RIMM缺失菌株和获救的白化表型emb15纯合突变体。RimM 结构域介导 EMB15 和质体核糖体蛋白 PRPS19 之间的相互作用。质体 16S rRNA 成熟在emb15 中也显着受损。这些观察结果表明，EMB15 在玉米种子发育中作为质体核糖体组装因子发挥作用，而 C 端结构域在正常条件下并不重要。