ALS2, encoding a plastid 50 S ribosomal protein L5, is essential for early chloroplast development in rice

Plastid ribosomal proteins (PRPs) are core components of the plastid translational machinery, playing indispensable roles in chloroplast biogenesis and plant growth. While the functions of some PRPs in rice have been characterized, the biological role of the plastid 50 S ribosomal protein L5 (PRPL5) remains unclear. Here, we characterize the function of Albino Lethal Seedling 2 (ALS2), encoding the PRPL5, in early chloroplast development. CRISPR/Cas9-mediated knockout of ALS2 resulted in seedling-lethal albino phenotypes, significantly reduced chlorophyll concentration, and disrupted chloroplast ultrastructure. ALS2 is highly expressed in rice leaves and its protein is localized in rice chloroplasts. Further analysis of gene expression revealed that nuclear and plastid genes participating in chloroplast development showed notable alterations in their expression in the als2 mutants. Notably, als2 mutants accumulated reactive oxygen species (ROS), particularly superoxide anions, which was accompanied by enhanced expression of ROS-scavenging genes and chlorophyll degradation genes. These findings demonstrate that ALS2 is essential for early chloroplast development in rice.