Genome assembly of the Chinese maize elite inbred line RP125 and its EMS mutant collection provide new resources for maize genetics research and crop improvement.

Maize is an important crop worldwide, as well as a valuable model with vast genetic diversity. Accurate genome and annotation information for a wide range of inbred lines would provide valuable resources for crop improvement and pan-genome characterization. In this study, we generated a high-quality de novo genome assembly (contig N50 of 15.43 Mb) of the Chinese elite inbred line RP125 using Nanopore long-read sequencing and Hi-C scaffolding, which yield highly contiguous, chromosome-length scaffolds. Global comparison of the RP125 genome with those of B73, W22, and Mo17 revealed a large number of structural variations. To create new germplasm for maize research and crop improvement, we carried out an EMS mutagenesis screen on RP125. In total, we obtained 5818 independent M2 families, with 946 mutants showing heritable phenotypes. Taking advantage of the high-quality RP125 genome, we successfully cloned 10 mutants from the EMS library, including the novel kernel mutant qk1 (quekou: "missing a small part" in Chinese), which exhibited partial loss of endosperm and a starch accumulation defect. QK1 encodes a predicted metal tolerance protein, which is specifically required for Fe transport. Increased accumulation of Fe and reactive oxygen species as well as ferroptosis-like cell death were detected in qk1 endosperm. Our study provides the community with a high-quality genome sequence and a large collection of mutant germplasm.

ROS-independent toxicity of Fe3O4 nanoparticles to yeast cells: Involvement of mitochondrial dysfunction.

Fe3O4 nanoparticles, one kind of magnetic nanomaterials (NMs), are widely used in drug delivery, biological imaging, sensors, catalysts and pollution management. However, its toxicity to biological systems and related toxicity mechanisms remain to be explored. In this study, we investigate the effect of as-synthesized Fe3O4 nanoparticles on growth of Saccharomyces cerevisiae, an important model fungus. Growth inhibition assays showed that Fe3O4 nanoparticles remarkably inhibited yeast growth. Interestingly, this inhibitory effect was not attributed to the well-known plasma membrane damage, cell wall damage and ROS accumulation. Further investigations revealed that the nanoparticles strongly impaired mitochondrial functions, resulting in abnormal mitochondrial morphology, decreased mitochondrial membrane potential (MMP) and attenuated ATP production. Most importantly, the respiratory chain complex Ⅳ, rather than other respiratory chain complexes and ATP synthases, was found to be the main target of the nanoparticles. This study uncovers a novel ROS-independent toxicity mechanism of Fe3O4 nanoparticles to eukaryotic cells.