CRISPR/Cas9-Mediated Knockout of BnaFAH Enhanced Brassica napus Resistance to Plutella xylostella Under a 2-Day Short-Day Photoperiod

The diamondback moth (Plutella xylostella) severely threatens global oilseed rape (Brassica napus L.) production. This study demonstrates that CRISPR/Cas9-mediated knockout of two homologous BnaFAH, involved in tyrosine degradation, confers enhanced Brassica napus resistance to Plutella xylostella under a 2-day short-day (SD2) photoperiod. Multi-omics analyses revealed that this resistance is associated with a coordinated response: BnaFAH deficiency triggers reactive oxygen species (ROS) accumulation, which is closely associated with activating the jasmonic acid (JA) biosynthetic and signaling pathways. This led to significant upregulation of key JA biosynthetic genes and accumulation of JA, its precursors (OPDA, OPC-4, and OPC-6), and bioactive conjugates (JA-Ile and JA-Phe). Pharmacological analyses support the central role of JA, as exogenous application of methyl jasmonate (MeJA) enhanced insect resistance, whereas the JA biosynthesis inhibitor DIECA suppressed resistance. Scavenging ROS with sodium selenite prevented both JA pathway upregulation and insect resistance, suggesting that ROS may act upstream to activate the JA biosynthetic and signaling pathways. These findings support a previously unrecognized “photoperiod-dependent ROS-JA” defense module, revealing how metabolic perturbation under specific environmental cues can be co-opted to enhance plant immunity, offering new targets for breeding resistant rapeseed varieties.