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Mitochondrial RNA polymerases (mtRNAPs) are necessary for the biogenesis of mitochondria and for proper mitochondrial function since they transcribe genes on mtDNA for tRNAs, rRNAs, and mRNAs. The unique type of RNA editing identified in mitochondria of Physarum polycephalum is thought to be closely associated with transcription, and as such, RNA editing activity would be expected to be closely associated with the mtRNAP. In order to better characterize the role of mtRNAPs in mitochondrial biogenesis and to determine the role of the Physarum mtRNAP in RNA editing, the cDNA of the Physarum mtRNAP was identified using PCR and degenerate primers designed from conserved motifs in mtRNAPs. This amplification product was used to screen a cDNA library for the cDNA corresponding to the Physarum mtRNAP. A cDNA corresponding to a 3.2 kb transcript containing a 997 codon open reading frame was identified. The amino acid sequence inferred from the open reading frame contains motifs characteristic of mtRNAPs. To confirm that a cDNA for an RNA polymerase had been isolated, the cDNA was expressed in E. coli as an N-terminal maltose binding protein (MBP) fusion protein. The fusion protein was purified by affinity chromatography and shown to have DNA-directed RNA polymerase activity. This functional mtRNAP will be useful for in vitro studies of mitochondrial transcription and RNA editing.

Plastid-encoded genes are coordinately transcribed by the nucleus-encoded RNA polymerase (NEP) and the plastid-encoded RNA polymerase (PEP). Resulting primary transcripts are frequently subject to RNA editing by cytidine-to-uridine conversions at specific sites. The physiological role of many editing events is largely unknown. Here, we have used the CRISPR/Cas9 technique in rice to knock out a member of the PLS-DYW subfamily of pentatricopeptide repeat (PPR) proteins. We found that OsPPR16 is responsible for a single editing event at position 545 in the chloroplast rpoB messenger RNA (mRNA), resulting in an amino acid change from serine to leucine in the β-subunit of the PEP. In striking contrast to loss-of-function mutations of the putative orthologue in Arabidopsis, which were reported to have no visible phenotype, knockout of OsPPR16 leads to impaired accumulation of RpoB, reduced expression of PEPdependent genes, and a pale phenotype during early plant development. Thus, by editing the rpoB mRNA, OsPPR16 is required for faithful plastid transcription, which in turn is required for Chl synthesis and efficient chloroplast development. Our results provide new insights into the interconnection of the finely tuned regulatory mechanisms that operate at the transcriptional and post-transcriptional levels of plastid gene expression.

This work dealt with a potential and effective method to reuse modified alginate beads after the removal of Cu­(II) ions for efficient adsorption of tetracycline (TC) from aqueous solutions. The modified alginate beads were fabricated by a polyacrylamide (PAM) network interpenetrated in alginate–Ca2+ network (PAM/CA) decorated with polyethylene glycol as a pore-forming agent. The porous PAM/CA was characterized using scanning electron microscopy, Brunauer–Emmett–Teller, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis. The adsorption kinetics, isotherms, adsorption stability, and reusability studies of the adsorbent toward Cu­(II) ions were scrutinized. The column performance of porous PAM/CA was tested with Cu­(II)-containing electroplating wastewater. After Cu­(II) adsorption, the Cu­(II)-adsorbed PAM/CA (PAM/CA@Cu) was applied to remove TC from aqueous solutions without any regeneration process. The effects of pH, initial TC concentration, ionic strength, and coexisting ions on the adsorption were also discussed in detail. Compared with many reported adsorbents, the PAM/CA@Cu exhibited an excellent adsorption performance toward TC with a maximum adsorption capacity of 356.57 mg/g predicted by the Langmuir model at pH 5.0 and 30 °C with the absence of coexisting ions. The possible adsorption mechanism of TC onto the PAM/CA@Cu was revealed.

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