Transcriptomic Insights on the Preventive Action of Apple (cv Granny Smith) Skin Wounding on Superficial Scald Development

Superficial scald is a post-harvest chilling storage injury leading to browning of the surface
of the susceptible cv Granny Smith apples. Wounding of skins has been reported to play a preventive
role on scald development however its underlying molecular factors are unknown. We have artificially
wounded the epidermal and sub-epidermal layers of apple skins consistently obtaining the
prevention of superficial scald in the surroundings of the wounds during two independent vintages.
Time course RNA-Seq analyses of the transcriptional changes in wounded versus unwounded skins
revealed that two transcriptional waves occurred. An early wave included genes up-regulated by
wounding already after 6 h, highlighting a specific transcriptional rearrangement of genes connected
to the biosynthesis and signalling of JA, ethylene and ABA. A later transcriptional wave, occurring
after three months of cold storage, included genes up-regulated exclusively in unwounded skins
and was prevented from its occurrence in wounded skins. A significant portion of these genes was
related to decay of tissues and to the senescence hormones ABA, JA and ethylene. Such changes
suggest a wound-inducible reversed hormonal balance during post-harvest storage which may
explain the local inhibition of scald in wounded tissues, an aspect that will need further studies for
its mechanistic explanation.