Differential low oxygen response and transcriptomic shifts drive fresh-cut lettuce deterioration in modified atmosphere packaging

Fresh-cut lettuce (Lactuca sativa) requires modified atmosphere packaging (MAP) with low oxygen (< 3 % O₂) to prevent enzymatic discoloration. However, some accessions exhibit rapid deterioration under these low oxygen conditions, resulting in significant product loss. This study investigated the mechanisms of this heritable deterioration, linked to the qSL4 locus, by examining respiration and transcriptomic responses. We found that rapid deterioration is associated with continued, albeit reduced, respiration under very low oxygen levels (<1 % O₂), with minimal effects from CO₂ and ethylene. Deterioration differences lessened at higher O₂ levels (∼20 %), emphasizing oxygen's critical role. RNA-seq analysis of slow (Salinas 88) and rapid (La Brillante) deteriorating cultivars revealed distinct early transcriptomic shifts under MAP. La Brillante upregulated more genes (1837) and downregulated fewer (1735) than Salinas 88 (1185 upregulated, 2367 downregulated), indicating higher metabolic activity in rapid deteriorating cultivar. Notably, glycolysis and electron transport chain (ETC) genes showed differential expression; ATP-consuming enzymes (fructokinase, hexokinase) and ETC complexes I and IV were upregulated in La Brillante but downregulated in Salinas 88. Conversely, Salinas 88 exhibited higher expression of alternative oxidase (AOX) genes, suggesting ATP conservation and reduced oxygen use. These findings indicate that slow-deteriorating genotypes maintain quality under low oxygen by limiting sugar and ATP consumption, while rapid deteriorating genotypes sustain higher metabolic activity, accelerating deterioration and likely shifting towards fermentation. This study provides insight into the early stages of lettuce deterioration and highlight the importance of low oxygen tolerance and metabolic adjustment capacity, setting the stage for future genomic research and functional studies on postharvest respiration and fermentation.