Identification and Gene Cloning of a Brittle Culm Mutant (bc22) in Rice

The mechanical strength of rice culm, an essential factor for lodging resistance and yield maintenance, is influenced by the composition and structure of the cell wall. In this study, we characterized a rice brittle culm mutant 22 (bc22), derived from LR005 through ethyl methanesulfonate (EMS) mutagenesis. The bc22 culm exhibited increased fragility and reduced mechanical strength compared to LR005. The mutant displayed pleiotropic effects, including a shorter plant height and panicle length, a smaller grain size, and the absence of the glume hairs. Scanning electron microscopy revealed a decrease in cell density and a looser structure in the bc22 culms. Biochemical analysis demonstrated a significant increase in hemicellulose content and a marked reduction in lignin content in the culm of bc22. Genetic analysis indicated that the brittle culm trait was governed by a single recessive gene. After employing bulked segregant analysis (BSA), whole-genome resequencing, and MutMap methods, LOC_Os02g25230 was identified as the candidate gene responsible for bc22. In bc22, a point mutation from proline (Pro) to leucine (Leu) in its coding region led to the pleiotropic phenotype. A complementation test further confirmed that the missense mutation causing the proline to leucine amino acid substitution in LOC_Os02g25230 was causative of the observed bc22 phenotype. Additionally, gene expression analysis showed that BC22 had higher expression levels in the culms, leaves, and spikelets compared to the roots. Taken together, our findings indicate that BC22 is a pleiotropic gene, and the influence of BC22 on brittleness may be associated with cell wall biosynthesis in rice culm.