Genome-Wide Identification of the FWL Gene Family in Rice Reveals Critical Roles in Abiotic Stress Response

The Fruit Weight 2.2-like (FWL) gene family, characterized by the conserved PLAC8 domain, plays important roles in plant organ development and metal ion homeostasis. However, the systematic characterization of FWL genes in rice (Oryza sativa) and their involvement in abiotic stress responses remain insufficiently understood. In this study, a genome-wide identification of the FWL gene family in rice was performed, resulting in the identification of nine OsFWL genes, including a previously unreported member, OsFWL9. Phylogenetic analysis of FWL proteins from rice, maize, soybean, and Arabidopsis thaliana classified the family into three distinct subgroups, indicating both conserved and divergent evolutionary relationships. Structural and conserved motif analyses revealed that OsFWL proteins share similar domain architectures, while promoter analysis uncovered abundant cis-acting elements associated with stress responses, phytohormone signaling, and plant growth and development. Expression profiling demonstrated that most OsFWL genes were rapidly induced by drought, high temperature, salt, and arsenic stresses at the seedling stage, suggesting their broad involvement in abiotic stress adaptation. Notably, OsFWL8 exhibited a unique expression pattern, being significantly suppressed under arsenic stress. Functional characterization using CRISPR/Cas9-generated knockout mutants and overexpression lines revealed that OsFWL8 negatively regulates arsenic tolerance in rice. Overexpression of OsFWL8 markedly increased plant sensitivity to arsenic stress. Furthermore, arsenic detoxification-related genes, including OsABCC1 and OsPCS2, were significantly upregulated in fwl8 mutants under arsenic treatment. These results indicate that OsFWL8 may modulate arsenic tolerance by influencing arsenic sequestration and detoxification pathways. Overall, this study provides a comprehensive overview of the FWL gene family in rice and identifies OsFWL8 as a key regulator of arsenic stress response, offering valuable insights for improving rice tolerance to heavy metal stress.