The plastid-encoded protein Orf2971 is required for protein translocation and chloroplast quality control.

Photosynthesis and the biosynthesis of many important metabolites occur in chloroplasts. In these semi-autonomous organelles, the chloroplast genome encodes approximately 100 proteins. The remaining chloroplast proteins, close to 3,000, are encoded by nuclear genes whose products are translated in the cytosol and imported into chloroplasts. However, there is still no consensus on the composition of the protein import machinery including its motor proteins and on how newly imported chloroplast proteins are refolded. In this study, we have examined the function of orf2971, the largest chloroplast gene of Chlamydomonas reinhardtii. The depletion of Orf2971 causes the accumulation of protein precursors, partial proteolysis and aggregation of proteins, increased expression of chaperones and proteases, and autophagy. Orf2971 interacts with the TIC (translocon at the inner chloroplast envelope) complex, catalyzes ATP (adenosine triphosphate) hydrolysis, and associates with chaperones and chaperonins. We propose that Orf2971 is intimately connected to the protein import machinery and plays an important role in chloroplast protein quality control.

Comparative impacts of iron oxide nanoparticles and ferric ions on the growth of Citrus maxima.

The impacts of iron oxide nanoparticles (γ-Fe2O3 NPs) and ferric ions (Fe3+) on plant growth and molecular responses associated with the transformation and transport of Fe2+ were poorly understood. This study comprehensively compared and evaluated the physiological and molecular changes of Citrus maxima plants as affected by different levels of γ-Fe2O3 NPs and Fe3+. We found that γ-Fe2O3 NPs could enter plant roots but no translocation from roots to shoots was observed. 20 mg/L γ-Fe2O3 NPs had no impact on plant growth. 50 mg/L γ-Fe2O3 NPs significantly enhanced chlorophyll content by 23.2% and root activity by 23.8% as compared with control. However, 100 mg/L γ-Fe2O3 NPs notably increased MDA formation, decreased chlorophyll content and root activity. Although Fe3+ ions could be used by plants and promoted the synthesis of chlorophyll, they appeared to be more toxic than γ-Fe2O3 NPs, especially for 100 mg/L Fe3+. The impacts caused by γ-Fe2O3 NPs and Fe3+ were concentration-dependent. Physiological results showed that γ-Fe2O3 NPs at proper concentrations had the potential to be an effective iron nanofertilizer for plant growth. RT-PCR analysis showed that γ-Fe2O3 NPs had no impact on AHA gene expression. 50 mg/L γ-Fe2O3 NPs and Fe3+ significantly increased expression levels of FRO2 gene and correspondingly had a higher ferric reductase activity compared to both control and Fe(II)-EDTA exposure, thus promoting the iron transformation and enhancing the tolerance of plants to iron deficiency. Relative levels of Nramp3 gene expression exposed to γ-Fe2O3 NPs and Fe3+ were significantly lower than control, indicating that all γ-Fe2O3 NPs and Fe3+ treatments could supply iron to C. maxima seedlings. Overall, plants can modify the speciation and transport of γ-Fe2O3 NPs or Fe3+ for self-protection and development by activating many physiological and molecular processes.