|Johnson, Franklin - Washington State University|
Submitted to: Horticulture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2015
Publication Date: 12/23/2015
Citation: Johnson, F.T., Zhu, Y. 2015. Transcriptome changes in apple peel tissues during CO2 injury symptom development under controlled atmosphere storage regimens. Horticulture Research. doi: 10.1038/hortres.2015.61.
Interpretive Summary: The advanced postharvest technologies such as controlled atmosphere (CA) storage regime and the application of the ethylene action blocker of 1-methylecyclopropane (1-MCP) can store apple fruit for an extended period with minimal loss of quality. However, fruit of some cultivars are known to have the propensity of developing physiological disorders such as external CO2 injury under CA storage regime. Application of 1-MCP had been reported to exacerbate the injury symptom. Current understanding of the molecular regulations leading to apple external CO2 development is very limited. The objective of this study was to examine the global molecular changes associated with CA storage regime and in response to 1-MCP application on 'Golden Delicious' fruit. Using most advanced RNA-seq platform and bioinformatic analyzing tools, transcripts of all activated genes were identified, quantified and categorized based on their functional annotation. According to their enrichment patterns to different functional categories, our transcriptome dataset revealed tremendous shift of cellular activity in the peel tissues of stored fruit per storage regime and duration. It appears that under the less stressful RA storage regime, cellular functions are able to overcome the stress originated from cold shock and therefore maintain the cellular integrity. However, the combined stress factors of cold temperature and CA storage condition, either acting additively or synergistically, caused additional transcriptomic changes in apple fruit peel tissue. Comparative transcriptomic analyses revealed that the imbalance of oxidative metabolism, enhanced glycolysis, and suppressed ethylene biosynthesis were specifically associated with CA storage regime. On the other hand, the necessary biological processes and pathways in the cell to mitigate the damaging stress levels and maintain the cellular integrity, such as ‘posttranslational protein modifications’ and ‘response to stress’, seemed to be compromised under CA storage regime. The reduced transcriptome changes due to 1-MCP application was associated with reduced CO2 injury symptom, which is probably due to the abolished ethylene responses and eliminated climacteric ripening process. The identified genes and their enrichment patterns to specific cellular processes provide an outline of molecular changes linked to the development of apple CO2 injury. The dataset will be a valuable contribution for future hypothesis-driven functional study on specific genes to elucidate their roles on apple fruit CO2 injury incidence.
Technical Abstract: 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-methylecyclopropane (1-MCP). However, CA storage can cause 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 in 'Golden Delicious' fruit peel tissue under different storage conditions and during development of CO2 injury were profiled. Fruit peel tissues under three different storage regimes of RA (regular cold atmosphere), CA and CAP (CA storage and 1-MCP treatment) were sampled at four storage durations over a 12-week period. Fruit physiological changes and CO2 injury symptoms were affected differently among these storage regimes. Identification of the differentially expressed genes (DEGs) and subsequent gene ontology enrichment analysis revealed the corresponding transcriptome changes associated with each storage regime. Overall, a stronger transcriptome change was associated with CA regimes as indicated by the larger numbers of DEGs. However, a lighter injury symptom observed in CAP was accompanied by reduced transcriptome changes. Furthermore, the higher enrichment levels compared to RA regime, in the oxidative stress response, glycolysis and protein posttranslational modification categories were specifically associated with the CA storage regime. Therefore, these processes potentially contribute to the development of apple external CO2 injury.