Transcriptome and metabolic survey disclose the mode of action of static and dynamic low oxygen postharvest storage strategies to prevent the onset of superficial scald disorder in fruit of 'Granny Smith' apple cultivar
To preserve quality feature and ensuring availability of fresh fruit on the market, apples need to be stored. The low temperature applied during storage, beside avoiding important fruit loss, can also promote the development of serious chilling injury type of disorder, such as superficial scald. One of the strategies largely employed to prevent the development of this phenomenon is the control of the storage atmosphere, by lowering down the concentration of oxygen. In this work, a multifaceted survey was carried out to investigate the variation in transcriptome together with three categories of metabolites (phenolics, lipids and volatile organic compounds, VOCs) in fruit of 'Granny Smith' apple cultivar stored in both static and dynamic hypoxia condition for 5 and 7 months, respectively. The global transcriptome survey identified a core set of differentially expressed genes in three main functional groups, revealing as the duration of storage had an important effect in the coordination of gene expression. The effect of the storage time was furthermore highlighted by the DEG-network analysis that identified a distinct number and type of transcriptomic hubs. Samples characterized by the development of superficial scald were distinguished by a higher concentration of chlorogenic acid and a higher expression of PAL and PPO in a time specific fashion. The prevention of this phenomenon was instead related to distinctive re-programming events, involving the accumulation of specific antioxidant types of metabolites, very long chain fatty acids and the expression of genes coordinating an hypoxia acclimation process, such as RAP2-like and PCO. Overall design: RNA-Seq analysis of apple peel. In total 36 samples have been assessed (6 samples: RA, RA_SL, DCA, DCA_SL, ULO, ULO_SL; x 2 times: T1 and T2; 3 replicates /sample; 6 samples x 2 times x 3 replicates: 36)