Transcriptome changes in apple peel tissues during CO2 injury symptom development under controlled atmosphere storage regimens
Apple (Malus × domestica Borkh.) is one of the most widely cultivated tree crops, and fruit storability is vital to the profitability of the apple fruit industry. Fruit of many apple cultivars can be stored for an extended period due to the introduction of advanced storage technologies, such as controlled atmosphere (CA) and 1-methylcyclopropane (1-MCP). However, CA storage can cause external CO2 injury for some apple cultivars. The molecular changes associated with the development of CO2 injury are not well elucidated. In this study, the global transcriptional regulations were investigated under different storage conditions and during development of CO2 injury symptoms on ‘Golden Delicious’ fruit. Fruit peel tissues under three different storage regimens, regular cold atmosphere, CA and CA storage and 1-MCP application were sampled at four storage durations over a 12-week period. Fruit physiological changes were affected differently under these storage regimens, and CO2 injury symptoms were detectable 2 weeks after CA storage. Identification of the differentially expressed genes and a gene ontology enrichment analysis revealed the specific transcriptome changes associated with each storage regimen. Overall, a profound transcriptome change was associated with CA storage regimen as indicated by the large number of differentially expressed genes. The lighter symptom was accompanied by reduced transcriptome changes under the CA storage and 1-MCP application regimen. Furthermore, the higher enrichment levels in the functional categories of oxidative stress response, glycolysis and protein post-translational modification were only associated with CA storage regime; therefore, these processes potentially contribute to the development of external CO2 injury or its symptom in apple.