OsRNE Encodes an RNase E/G-Type Endoribonuclease Required for Chloroplast Development and Seedling Growth in Rice

Chloroplast biogenesis is a crucial biological process in plants. Endoribonuclease E (RNase E) functions in the RNA metabolism of chloroplast and plays a vital role for chloroplast development in <i>Arabidopsis</i>. However, despite sharing 44.7% of its amino acid sequence identity with <i>Arabidopsis</i> RNase E, the biological function of rice OsRNE (<i>Oryza sativa</i> RNase E) remains unknown. Here, we identified a <i>white leaf and lethal 1</i> (<i>wll1</i>) mutant that displayed white leaves and died at the seedling stage. The causal gene <i>OsRNE</i> was isolated by MutMap+ method. CRISPR/Cas9-mediated knockout of <i>OsRNE</i> resulted in white leaves and seedling lethality, confirming <i>OsRNE</i> as the causal gene for the <i>wll1</i> phenotype. The albino phenotype of <i>osrne</i> mutant was associated with decreased chlorophyll content and abnormal thylakoid morphology in the chloroplast. The absence of <i>OsRNE</i> led to a significant reduction in the Rubisco large subunit (RbcL), and the 23S and 16S chloroplast rRNAs were nearly undetectable in the <i>osrne</i> mutant. <i>OsRNE</i> transcripts were highly expressed in green tissues, and the protein was localized to chloroplasts, indicating its essential role in photosynthetic organs. Furthermore, transcriptome analysis showed that most of the genes associated with photosynthesis and carbohydrate metabolism pathways in the <i>osrne</i> mutant were significantly down-regulated compared with those in WT. Chlorophyll- and other pigment-related genes were also differentially expressed in the <i>osrne</i> mutant. Our findings demonstrated that OsRNE plays an important role in chloroplast development and chlorophyll biosynthesis in rice.