Cucumber fruit is susceptible to chilling injury (CI) under cold storage conditions. The application of melatonin can mitigate CI in cucumber fruit; however, the underlying molecular mechanisms are not well understood. Polyamines (PAs) are important biomolecules that have regulatory roles in cold stress responses, and this study identified 15 PAs-encoding gene members in cucumber by using bioinformatics techniques and their genome attributes were characterized. The cucumber fruit was treated with 100 µM melatonin for 15 min and stored for 15 d at 4 °C. The results showed that melatonin reduced the CI levels. Similarly, melatonin treatment reduced the incidence of decay and inhibited malonaldehyde content and ion leakage. Among the identified PAs member genes, and were upregulated in melatonin-treated fruits. Besides, CsMYB44 expression is upregulated by cold stress and melatonin treatment. Thus, CsMYB44 TF was cloned from cucumber fruit. Furthermore, subcellular localization experiments showed that CsMYB44 is localized in the cell nucleus. The yeast two-hybrid assay revealed the self-activation capacity of CsMYB44. Additionally, a dual-luciferase assay revealed that CsMYB44 acts as a transcriptional activator of the corresponding promoters of , and . Similarly, luciferase complementation imaging revealed intense fluorescence in the CsMYB44-injected tobacco leaves. These findings suggest that CsMYB44 plays a transcriptional activator role in PAs genes, alleviating CI, and providing helpful insights into postharvest cold storage tolerance in cucumber fruit.

中文翻译：

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褪黑素通过 CsMYB44 介导的多胺生物合成基因家族转录激活提高黄瓜的冷藏耐受性

黄瓜果实在冷藏条件下容易受到冷害（CI）。施用褪黑素可减轻黄瓜果实CI；然而，潜在的分子机制尚不清楚。多胺（PAs）是重要的生物分子，在冷应激反应中具有调节作用，本研究利用生物信息学技术鉴定了黄瓜中15个PAs编码基因成员，并对其基因组属性进行了表征。黄瓜果实用 100 µM 褪黑激素处理 15 分钟，并在 4 °C 下保存 15 d。结果表明，褪黑激素降低了 CI 水平。同样，褪黑激素治疗降低了腐烂的发生率并抑制了丙二醛含量和离子泄漏。在已鉴定的 PA 成员基因中， 和 在经褪黑激素处理的水果中表达上调。此外，冷应激和褪黑激素处理会上调CsMYB44的表达。因此，CsMYB44 TF是从黄瓜果实中克隆的。此外，亚细胞定位实验表明CsMYB44定位于细胞核。酵母双杂交实验揭示了 CsMYB44 的自我激活能力。此外，双荧光素酶测定表明，CsMYB44 充当 、 和 的相应启动子的转录激活子。同样，荧光素酶互补成像显示注射 CsMYB44 的烟叶中存在强烈的荧光。这些发现表明 CsMYB44 在 PAs 基因中发挥转录激活剂作用，减轻 CI，并为黄瓜果实采后冷藏耐受性提供有用的见解。