Table_3_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.

苹果贮藏期间通常用于抑制果实腐烂的低温环境，反而可能诱发一种名为苹果虎皮病（superficial scald）的冷害病症。本研究以‘澳洲青苹（Granny Smith）’与‘拉迪娜（Ladina）’两个苹果品种为材料，探究了该病症的发病机理，以及两种防控策略的作用机制：分别为1-甲基环丙烯（1-methylcyclopropene，1-MCP）浸渍处理，以及低氧浓度贮藏。代谢组分析结果显示，特定代谢物发生了重编程，尤以黄烷-3-醇类与不饱和脂肪酸类物质最为显著；而全基因组转录组分析则将差异表达基因（Differentially Expressed Genes，DEGs）划分为四个功能聚类簇。京都基因与基因组百科全书（KEGG）通路分析、基因本体（GO）富集分析，结合基因-代谢物互作组的结果表明：1-MCP处理可通过主动促进不饱和脂肪酸的合成，抑制苹果虎皮病的发生，这一效应在澳洲青苹品种中尤为显著。而对苹果虎皮病更易感、且对防控策略响应更弱的拉迪娜苹果品种，则表现出超长链脂肪酸的更高积累量。低氧贮藏处理可诱导两个苹果品种中乙醇与乙醛的积累量升高，同时上调厌氧呼吸相关基因的表达，包括苹果酸脱氢酶、乙醇脱氢酶以及丙酮酸脱羧酶。与1-MCP同理，低氧处理可通过直接调控乙烯信号，抑制编码多酚氧化酶（PPO）的PPO基因的表达——该酶负责催化绿原酸的氧化反应，从而阻止苹果虎皮病的发生。此外，在澳洲青苹中，研究还检测到乙烯响应因子（Ethylene Response Factor，ERF）家族VII亚家族的三个成员的表达发生改变，这类基因编码的蛋白可协调植物的低氧适应过程。全转录组RNA测序（RNA-Seq）的整体表达模式还揭示了两个苹果品种间特有的转录组特征，阐明了不同遗传背景对该病症调控的影响。