Knockdown of OsCOI1 increases rice yield under normal conditions and compromises thermotolerance during panicle differentiation

Knockdown of OsCOI1 boosts yield under NT yet is essential for thermotolerance during the panicle differentiation stage. HS disrupts C-N balance and antioxidant defense in the OsCOI1 mutant, severely inhibiting spikelet differentiation and causing excessive yield loss. Exogenous MeJA mitigated heat damage in WT but not in OsCOI1 mutants, demonstrating that OsCOI1 is indispensable for JA-mediated regulation under HS. Although jasmonate (JA) signaling participates in heat stress (HS) responses, the mechanism by which it balances spikelet development and yield stability via the OsCOI1 gene remains unclear, particularly under HS during the panicle differentiation stage (PDS). This study comprehensively examined the influence of HS on panicle architecture, carbon (C) and nitrogen (N) metabolism, accumulation and allocation, root oxidative activity, antioxidant enzyme activity, JA and methyl jasmonate (MeJA) contents, yield and yield components using wild-type rice (WT, Nipponbare) and the coi1-18 mutant ( OsCOI1 knockdown mutant, blocked JA signaling). The results demonstrated that under normal temperature (NT) conditions, the coi1-18 mutant exhibited significantly higher grain number per panicle, grain setting rate, and 1000-grain weight relative to the WT, collectively increasing grain yield by 23.2%. Conversely, under HS, reduced JA and MeJA contents in the coi1-18 mutant resulted in enhanced heat sensitivity, diminished antioxidant capacity, and dysregulated C-N metabolism. These effects markedly suppressed spikelet differentiation, thereby causing a yield reduction in the coi1-18 mutant that was 16.1 percentage points greater than in WT. Exogenous MeJA application effectively mitigated HS-induced suppression of spikelets differentiation in WT but failed to significantly rescue the phenotype in the coi1-18 mutant. This study reveals OsCOI1 as a context-dependent regulator: knockdown of OsCOI1 enhances yield under NT but impairs HS tolerance during PDS. This indicates a breeding-relevant trade-off and suggests that modulating JA signaling could balance yield under NT with panicle protection under HS.