Fig. 9.
A working model for the role of OsPPR16 during chloroplast development in rice. During early chloroplast development, OsPPR16 is particularly important to edit rpoB transcripts to ensure maximum RpoB accumulation, thereby producing an active plastid‐encoded RNA polymerase (PEP) pool that is capable of efficiently transcribing PEP‐dependent genes (PDGs). The accumulation of tRNAGlu and proteins encoded by other PEP‐dependent genes is required to meet the demand for Chl and protein synthesis during the rapid development of proplastids into chloroplasts. Loss of OsPPR16 leads to an extremely low level of tRNAGlu (and proteins encoded by other PEP‐dependent genes, PPDGs), thereby limiting Chl biosynthesis and protein synthesis (and, potentially, also protein stability in the absence of sufficient pigments for incorporation into Chl‐binding proteins) in the developing chloroplasts, thus causing the pale phenotype during early leaf development. Lower demands for PEP activity at later developmental stages and gradually increasing PEP accumulation in the mutants alleviate the phenotype and facilitate leaf greening. See the Discussion section for more details.