Evidence for pre-climacteric activation of AOX transcription during cold-induced conditioning to ripen in European pear (Pyrus communis L.)

European pears (Pyrus communis L.) require a range of cold-temperature exposure to induce ethylene biosynthesis and fruit ripening. Physiological and hormonal responses to cold temperature storage in pear have been well characterized, but the molecular underpinnings of these phenomena remain unclear. An established low-temperature conditioning model was used to induce ripening of ‘D’Anjou’ and ‘Bartlett’ pear cultivars and quantify the expression of key genes representing ripening-related metabolic pathways in comparison to non-conditioned fruit. Physiological indicators of pear ripening were recorded, and fruit peel tissue sampled in parallel, during the cold-conditioning and ripening time-course experiment to correlate gene expression to ontogeny. Two complementary approaches, Nonparametric Multi-Dimensional Scaling and efficiency-corrected 2-(ΔΔCt), were used to identify genes exhibiting the most variability in expression. Interestingly, the enhanced alternative oxidase (AOX) transcript abundance at the pre-climacteric stage in ‘Bartlett’ and ‘D’Anjou’ at the peak of the conditioning treatments suggests that AOX may play a key and a novel role in the achievement of ripening competency. There were indications that cold-sensing and signaling elements from ABA and auxin pathways modulate the S1-S2 ethylene transition in European pears, and that the S1-S2 ethylene biosynthesis transition is more pronounced in ‘Bartlett’ as compared to ‘D’Anjou’ pear. This information has implications in preventing post-harvest losses of this important crop.

欧洲梨（Pyrus communis L.）需经历一定范围的低温暴露，以诱导乙烯生物合成与果实成熟。针对梨低温贮藏的生理与激素响应已得到充分阐释，但此类现象背后的分子基础仍不明确。本研究采用已成熟的低温预处理模型，诱导‘D'Anjou’与‘Bartlett’两个梨品种的果实成熟，并与未预处理的果实对照，定量分析代表成熟相关代谢通路的关键基因的表达水平。在低温预处理与成熟的时间进程实验中，同步记录梨成熟的生理指标，并并行采集果皮组织样本，以关联基因表达与个体发育进程。研究采用两种互补分析方法——非参数多维缩放（Nonparametric Multi-Dimensional Scaling）与效率校正的2-(ΔΔCt)法，筛选出表达差异最显著的基因。值得注意的是，在预处理峰值阶段，‘Bartlett’与‘D'Anjou’梨的呼吸跃变前期样本中，交替氧化酶（AOX）的转录本丰度显著升高，这提示AOX可能在果实成熟能力的获得中发挥关键且新颖的作用。有迹象表明，脱落酸（ABA）与生长素通路中的低温感知及信号元件，可调控欧洲梨的S1-S2乙烯转变；且相较于‘D'Anjou’梨，‘Bartlett’梨的S1-S2乙烯生物合成转变更为明显。该研究结果可为防止这一重要经济作物的采后损失提供参考依据。