Comparative analysis of room-temperature ripening and ethylene-amplified ripening reveals shared ripening outputs but distinct transcriptional intensities in kiwifruit

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Kiwifruit is a climacteric fruit that can ripen after harvest through more than one physiological route. In untreated fruit, gradual ripening may occur under room-temperature conditions even when ethylene production remains undetectable, whereas exogenous ethylene triggers rapid ripening and autocatalytic ethylene production. To distinguish these processes, we compared temperature-induced ripening under room-temperature air treatment with ethylene-induced ripening after exposure to 100 μL/L ethylene. Physiological traits, starch content, soluble sugars, amyloplast ultrastructure and transcriptome profiles were analyzed across ripening stages. Temperature-induced fruit showed slow firmness loss, moderate respiration changes and moderate starch-to-sugar conversion while ethylene production remained undetectable. Ethylene-induced fruit showed rapid firmness loss, enhanced respiration, autocatalytic ethylene production, accelerated starch degradation and stronger accumulation of soluble sugars. Relative-change analysis further showed that ethylene induction caused substantially higher firmness-loss, starch-degradation and calculated soluble-sugar-increase rates than temperature induction. Transcriptome profiling separated the two ripening trajectories, with the strongest ethylene-associated transcriptional divergence occurring at 2–3 d after treatment. Functional categorization and representative gene analysis showed that carbohydrate metabolism and cell-wall remodeling were shared ripening outputs, whereas exogenous ethylene strongly amplified genes associated with ethylene biosynthesis/signaling ( ACS, ACO / ACO3 and ERF ), starch and sugar metabolism ( BAM, SPS and CINV ), and cell-wall remodeling ( PG, EXPA, BGAL and XTH / XTR ). These results support a model in which room-temperature treatment initiates a slow temperature-induced ripening program under undetectable ethylene production, while exogenous ethylene accelerates ripening by amplifying shared metabolic and structural modules. This comparative framework improves the mechanistic interpretation of kiwifruit ripening and provides physiological and molecular information for controlling ready-to-eat fruit quality.

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