Mutations and rearrangements of mitochondrial genes cause plant cytoplasmic male sterility. It is a significant way to utilize hybrid vigor to enhance crop yield. Ogu cytoplasmic male sterility (CMS) is a natural cytoplasmic male sterility type discovered in radishes, being successfully transferred to rapeseed and cruciferous vegetables. However, current studies lack depth in exploring the molecular mechanisms of its male sterility. This study confirmed that orf138 is the causal gene for Ogu CMS through the genetic transformation in Arabidopsis. Transcriptome analysis of aborted anthers in different stages suggested that differentially expressed genes (DEGs) are mainly enriched in pathways such as glycerophospholipid metabolism and arginine and proline metabolism. It reveals that key genes involved in lipid metabolism pathways are significantly down-regulated in the sterile line (OguA), including BnaGPAT1, localized within the tapetum mitochondrial and endoplasmic reticulum. This could lead to changes in the metabolism of substances like acylglycerols within the tapetum, causing disruptions in lipid metabolism. This is consistent with morphological and subcellular structural changes in the tapetum and microspore cells, as observed in the transmission electron microscopy. This abnormal lipid metabolism may trigger specific reactive oxygen species (ROS) accumulation in an oxidative stress response, ultimately leading to an aborted microspore. Our study based on transcriptome has deepened our understanding of the molecular mechanisms in Ogu CMS.

Mature chloroplasts, as the main sites of photosynthesis, are essential for seedling growth in higher plants. Loss of function of genes involved in chloroplast development changes plant phenotype. We obtained a YELLOW COTYLEDON (YCO) mutant in rapeseed (Brassica napus L.) using CRISPR-Cas9. Bn.YCO, a gene of unknown function, has two homologous copies (BnaA01.YCO and BnaC01.YCO) in B. napus. Homozygous mutation of these two homologs resulted in yellow cotyledons and chlorotic true leaves. Transmission electron microscopy revealed that the formation of thylakoid membranes was inhibited in yellow cotyledons. Sequence similarity search revealed that YCO was conserved in different species, and a subcellular location assay verified that Bn.YCO was located in the chloroplast. Bn.YCO was expressed in multiple tissues, most highly in cotyledons. Knockout of Bn.YCO blocked the transcription of plastid genes, especially those of photosystem genes transcribed by plastid-encoded polymerase. Transcriptome sequencing showed that the majority of genes involved in ribosome assembly and photosynthesis were down-regulated in Bn.yco mutants. These results suggested that loss of function of Bn.YCO affected plastid gene transcription, which influenced chloroplast biogenesis in rapeseed seedlings.