Rapeseed (Brassica napus) is an essential oil resource, but its yield can be significantly compromised by Sclerotinia sclerotiorum (S. sclerotiorum) infection. Due to the absence of rapeseed strains that are highly or completely immune to S. sclerotiorum, enhancing rapeseed resistance through genetic approaches is challenging. In this study, we developed a novel method to enhance rapeseed resistance to S. sclerotiorum using β-ocimene. Our results demonstrated that β-ocimene treatment significantly strengthened the defense capabilities of rapeseed. β-ocimene treatment can simultaneously activate multiple defense-related signaling pathways, including jasmonic acid signaling, salicylic acid signaling, and MAPK signaling, in rapeseed, while also inducing the accumulation of secondary metabolites coniferyl aldehyde—a key secondary metabolite in the phenylpropanoid pathway critical for plant defense responses. Furthermore, applying coniferyl aldehyde to the leaves of rapeseed can remarkably enhance its resistance to sclerotinia disease. Collectively, these findings confirm that β-ocimene activates the defense system of rapeseed, elevates the content of coniferyl aldehyde, and thereby enables rapeseed to effectively combat sclerotinia disease. The metabolomics data are available via MetaboLights under the identifier MTBLS12510. In conclusion, this study not only uncovers the mechanism by which β-ocimene induces rapeseed resistance to sclerotinia disease but also presents a novel approach for its prevention and control.

Rapeseed (Brassica napus L.) growth and productivity are severely constrained by drought stress worldwide. Stomata are central regulators of plant transpiration and gas exchange, and therefore, represent key targets for enhancing water-use efficiency and drought tolerance. The transcription factor ABSCISIC ACID INSENSITIVE 4 (ABI4), a key regulator of the abscisic acid (ABA) signaling pathway, plays crucial roles in plant abiotic stress responses and stomatal regulation. Nevertheless, the biological functions of BnaABI4 in B. napus remain largely unclear. In this study, four BnaABI4 paralogs were identified in the elite rapeseed cultivar ZS11 through genome-wide identification and comprehensive bioinformatic analyses. Each BnaABI4 protein harbors only one conserved AP2 domain, and their promoters contain multiple stress/hormone-responsive cis-regulatory elements (CREs). We subsequently generated BnaABI4-4 overexpression (OE) lines as well as BnaABI4 CRISPR/Cas9-mediated knockout (KO) transgenic lines. Phenotypic assays demonstrated that OE line had reduced transpiration rate (Tr), stomatal conductance (Gs) and stomatal density, along with enhanced drought tolerance, whereas KO lines showed the opposite phenotype. Transcriptome profiling identified numerous differentially expressed genes (DEGs) enriched in biological pathways associated with stomatal regulation, ABA signal transduction, and drought acclimation. Further Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses confirmed significant enrichment of DEGs in processes including stomatal development, stomatal movement, reactive oxygen species (ROS) homeostasis, and drought tolerance. Collectively, our findings demonstrate that BnaABI4 negatively regulates stomatal density while positively contributing to drought tolerance in B. napus. This study lays a mechanistic foundation for genetic improvement and molecular breeding of drought-tolerant rapeseed cultivars.