Disruption of a Rice Chloroplast-Targeted Gene OsHMBPP Causes a Seedling-Lethal Albino Phenotype

Chloroplast development is coordinately regulated by plastid- and nuclear-encoding genes. Although many regulators have been reported to be involved in chloroplast development, new factors remain to be identified, given the complexity of this process. In this study, we characterized a rice mutant lethal albinic seedling 1(las1)form of a 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (OsHMBPP) that was targeted to the chloroplasts. The LAS1 mutation caused the albino lethal phenotype in seedlings. Transmission electron microscopy indicated that las1 were defective in early chloroplast development. LAS1 is preferentially expressed in leaves, implying its role in controlling chloroplast development. The expression levels of many chloroplast-encoded genes were altered significantly in las1. The expression levels of nuclear-encoded gene involved in Chl biosynthesis were also decreased in las1. We further investigated plastidic RNA editing in las1 and found that the edit efficiency of four chloroplast genes were markly altered. Compared with WT, las1 exhibited defective in biogenesis of chloroplast ribosomes. Our results show that LAS1/OsHMBPP plays an essential role in the early chloroplast development in rice.