Abstract
Extensive studies have been carried out on chloroplast gene expression and chloroplast development; however, the regulatory mechanism is still largely unknown. Here, we characterized Pigment-Defective Mutant4 (PDM4), a P-type PPR protein localized in chloroplast. The pdm4 mutant showed seedling-lethal and albino phenotype under heterotrophic growth conditions. Transmission electron microscopic analysis revealed that thylakoid structure was totally disrupted in pdm4 mutant and eventually led to the breakdown of chloroplasts. The levels of several chloroplast- and nuclear-encoded proteins are strongly reduced in pdm4 mutant. Besides, transcript profile analysis detected that, in pdm4 mutant, the expression of plastid-encoded RNA polymerase-dependent genes was markedly affected, and deviant chloroplast rRNA processing was also observed. In addition, we found that PDM4 functions in the splicing of group II introns and may also be involved in the assembly of the 50S ribosomal particle. Our results demonstrate that PDM4 plays an important role in chloroplast gene expression and chloroplast development in Arabidopsis.
Highlights
Chloroplasts are known for providing energy and carbon resource to the plant cell and are indispensable for plant development and growth (Bryant et al, 2011)
To identify pentatricopeptide repeat (PPR) genes involved in chloroplast development, we screened a collection of T-DNA inserted mutation lines localized in PPR genes (Du et al, 2017; Zhang J. et al, 2017)
These works suggest that most functional PPR proteins located in the chloroplast mainly play a critical role in accumulation of chlorophyll and are essential for plant survival
Summary
Chloroplasts are known for providing energy and carbon resource to the plant cell and are indispensable for plant development and growth (Bryant et al, 2011). Derived from cyanobacterial ancestors, the chloroplasts belong to semi-autonomous organelles which possess their own genomes. Over the last billion years, the chloroplast genome has lost numerous genes in higher plants and generally remains about 120 genes which encode primary components of translation, transcription, and photosynthesis apparatus, as well as contains some critical biogenesis-related genes such as accD, clpP1, matK, ycf, and ycf (Sato et al, 1999; Leister, 2003; Ouyang et al, 2017). The chloroplast genome is small and with limited coding information, the transcriptional process is much more complex than that of prokaryotes which are usually organized in polycistronic transcriptional units. RNA processing from polycistronic precursors and editing are strikingly different between chloroplast and prokaryotes (Sugita and Sugiura, 1996; Sato et al, 1999).
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