bims-plasge 2020-11-15 papers

Proc Natl Acad Sci U S A. 2020 Nov 09. pii: 202004075. [Epub ahead of print]

Rerouting of ribosomal proteins into splicing in plant organelles.

Chuande Wang, Rachel Fourdin, Martine Quadrado, Céline Dargel-Graffin, Dimitri Tolleter, David Macherel, Hakim Mireau.

Production and expression of RNA requires the action of multiple RNA-binding proteins (RBPs). New RBPs are most often created by novel combinations of dedicated RNA-binding modules. However, recruiting existing genes to create new RBPs is also an important evolutionary strategy. In this report, we analyzed the eight-member uL18 ribosomal protein family in Arabidopsis uL18 proteins share a short structurally conserved domain that binds the 5S ribosomal RNA (rRNA) and allows its incorporation into ribosomes. Our results indicate that Arabidopsis uL18-Like proteins are targeted to either mitochondria or chloroplasts. While two members of the family are found in organelle ribosomes, we show here that two uL18-type proteins function as factors necessary for the splicing of certain mitochondrial and plastid group II introns. These two proteins do not cosediment with mitochondrial or plastid ribosomes but instead associate with the introns whose splicing they promote. Our study thus reveals that the RNA-binding capacity of uL18 ribosomal proteins has been repurposed to create factors that facilitate the splicing of organellar introns.

Keywords: chloroplasts; intron splicing; mitrochondria; plants; ribosomal protein

DOI: https://doi.org/10.1073/pnas.2004075117

Photosynth Res. 2020 Nov 08.

A pentatricopeptide repeat protein DUA1 interacts with sigma factor 1 to regulate chloroplast gene expression in Rice.

Yanxin Du, Weiping Mo, Tingting Ma, Weijiang Tang, Lijin Tian, Rongcheng Lin.

Chloroplast gene expression is controlled by both plastid-encoded RNA polymerase (PEP) and nuclear-encoded RNA polymerase and is crucial for chloroplast development and photosynthesis. Environmental factors such as light and temperature can influence transcription in chloroplasts. In this study, we showed that mutation in DUA1, which encodes a pentatricopeptide repeat (PPR) protein in rice (Oryza sativa), led to deficiency in chloroplast development and chlorophyll biosynthesis, impaired photosystems, and reduced expression of PEP-dependent transcripts at low temperature especially under low-light conditions. Furthermore, we demonstrated that sigma factor OsSIG1 interacted with DUA1 in vitro and in vivo. Moreover, the levels of chlorophyll and PEP-dependent gene expression were significantly decreased in the Ossig1 mutants at low-temperature and low-light conditions. Our study reveals that the PPR protein DUA1 plays an important role in regulating PEP-mediated chloroplast gene expression through interacting with OsSIG1, thus modulates chloroplast development in response to environmental signals.

Keywords: Chloroplast development; Light; PEP; PPR; Sigma factor

DOI: https://doi.org/10.1007/s11120-020-00793-0

J Exp Bot. 2020 Nov 09. pii: eraa528. [Epub ahead of print]

Arabidopsis ORANGE protein regulates plastid preprotein import through interacting with Tic proteins.

Hui Yuan, Emily G Pawlowski, Yong Yang, Tianhu Sun, Theodore W Thannhauser, Michael Mazourek, Danny Schnell, Li Li.

Chloroplast targeted proteins are actively imported into chloroplasts via the machinery spanning the double layered membranes of chloroplasts. While the key translocons at the outer (TOC) and inner (TIC) membranes of chloroplasts are defined, proteins that interact with the core components to facilitate preprotein import are continuously being discovered. A DnaJ-like chaperone ORANGE (OR) protein is known to regulate carotenoid biosynthesis as well as plastid biogenesis and development. In this study, we found that OR physically interacts with several Tic proteins including Tic20, Tic40, and Tic110 in the classic TIC core complex of the chloroplast import machinery. Knocking out or and its homologous gene or-like greatly affects the import efficiency of some photosynthetic and non-photosynthetic preproteins. Consistent with the direct interactions of OR with Tic proteins, the binding efficiency assay revealed that the effect of OR likely occurs at translocation at the inner envelope membrane (i.e. at the TIC complex). OR is able to reduce Tic40 protein turnover rate through its chaperone activity. Moreover, OR was found to interfere with the interaction between Tic40 and Tic110, and reduces the binding of preproteins to Tic110 in aiding their release for translocation and processing. Our findings suggest that OR plays a new and regulatory role in stabilizing key translocons and in facilitating the late stage of plastid preprotein translocation to regulate plastid preprotein import.

Keywords: OR; Plastid import machinery; Tic110; Tic40; import efficiency; protein-protein interaction

DOI: https://doi.org/10.1093/jxb/eraa528