Table_14_Comparative transcriptome and metabolite survey reveal key pathways involved in the control of the chilling injury disorder superficial scald in two apple cultivars, ‘Granny Smith’ and ‘Ladina’.xlsx

The low temperature normally applied to prevent fruit decay during the storage of apples, can also triggers the onset of a chilling injury disorder known as superficial scald. In this work, the etiology of this disorder and the mechanism of action of two preventing strategies, such as the application of 1-MCP (1-methylcyclopropene) and storage at low oxygen concentration in ‘Granny Smith’ and ‘Ladina’ apple cultivars were investigated. The metabolite assessment highlighted a reorganization of specific metabolites, in particular flavan-3-ols and unsaturated fatty acids, while the genome-wide transcriptomic analysis grouped the DEGs into four functional clusters. The KEGG pathway and GO enrichment analysis, together with the gene-metabolite interactome, showed that the treatment with 1-MCP prevented the development of superficial scald by actively promoting the production of unsaturated fatty acids, especially in ‘Granny Smith’. ‘Ladina’, more susceptible to superficial scald and less responsive to the preventing strategies, was instead characterized by a higher accumulation of very long chain fatty acids. Storage at low oxygen concentration stimulated a higher accumulation of ethanol and acetaldehyde together with the expression of genes involved in anaerobic respiration, such as malate, alcohol dehydrogenase and pyruvate decarboxylase in both cultivars. Low oxygen concentration, likewise 1-MCP, through a direct control on ethylene prevented the onset of superficial scald repressing the expression of PPO, a gene encoding for the polyphenol oxidase enzyme responsible of the oxidation of chlorogenic acid. Moreover, in ‘Granny Smith’ apple, the expression of three members of the VII subgroups of ERF genes, encoding for elements coordinating the acclimation process to hypoxia in plants was observed. The global RNA-Seq pattern also elucidated a specific transcriptomic signature between the two cultivars, disclosing the effect of the different genetic background in the control of this disorder.

在苹果储存过程中，为防止果实腐烂而通常采用的低温处理，亦可能诱发一种称为表面焦烧的冷害病症。本研究对这一病症的病因以及两种预防策略的作用机制进行了探讨，这两种策略包括在‘Granny Smith’和‘Ladina’苹果品种中应用1-MCP（1-甲基环丙烯）以及降低氧气浓度储存。代谢物评估揭示了特定代谢物的重新组织，特别是黄酮醇和未饱和脂肪酸，而全基因组转录组分析将差异表达基因（DEGs）分为四个功能簇。KEGG通路和GO富集分析，连同基因-代谢物互作网络，表明1-MCP处理通过积极促进不饱和脂肪酸的产生，尤其是‘Granny Smith’品种，从而有效预防了表面焦烧的发生。对‘Ladina’这一对表面焦烧更为敏感且对预防策略反应较弱的品种，其特征是长链脂肪酸的积累量更高。在两种品种中，低氧浓度储存刺激了乙醇和乙醛的更高积累，以及参与厌氧呼吸的基因（如苹果酸、酒精脱氢酶和丙酮酸脱羧酶）的表达。同样地，低氧浓度，如同1-MCP，通过直接控制乙烯来防止表面焦烧的发生，抑制了PPO基因的表达，该基因编码的酶负责氯原酸的氧化。此外，在‘Granny Smith’苹果中，观察到ERF基因VII亚组的三个成员的表达，这些基因编码的蛋白质负责植物对缺氧的适应性调节过程。全局RNA-Seq模式也阐明了两种品种之间的特定转录组特征，揭示了不同遗传背景在控制这一病症中的作用。