Physiological effects and transcriptome analysis of peach fruit with different maturity after 1-MCP treatment

Abstract:【Objective】1-methylcyclopropene (1-MCP), known to block ethylene receptors, which has improved application potential in fruit ripening and in cut flowers. Melting flesh peach is a typical respi- ratory climacteric fruit which softens quickly and susceptible to infections by pathogenic bacteria, thus causing severe economic losses. Limited studies related to 1-MCP treatment on postharvest physiologi- cal effects during peach fruit by high-throughput sequencing technology were reported. In this study, to identify the differentially expressed genes (DEGs) including the genes involved in fruit ripening, hor- mones and polypeptide under 1- MCP treatment, the molecular mechanisms of 1- MCP treatment on peach fruit by high-throughput sequencing was explored【. Methods】The melting flesh‘CN13’was grown in Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences.‘CN13’fruits were collected at 80 and 85 days after flowering (DAF) (designated S4 I and S4 II, respective-ly), S4 I represents the stage corresponding to class 0 (pre-climacteric), S4 II represents the stage cor- responding to class 1 (onset of climacteric), and was treated with 1-MCP at the concentration of 10 mmol·L-1 for 24 h. Ethylene and firmness were measured by gas chromatography and penetrometer re- spectively. The cDNA library was constructed and analyzed using Illumina HiSeq 2500. Align and anno- tate reference genome sequences with software Tophat. The software HTSeq was used to analyze the difference level; the software DEGSeq was used to analyze the differential gene expression. The soft- ware GOSeq and KOBAS were used to perform GO enrichment analysis and KEGG enrichment analy- sis of differentially expressed gene. Predictive analysis of transcription factors was done by using iTAK software.【Results】In pre-climacteric, 1-MCP was effective in both reducing ethylene emission and fruit firmness, while in onset of climacteric, 1-MCP effect was intermediate, the inhibitor induced ethyl- ene production but was able to delay fruit softening. The transcriptome of 24 h treatment with 1-MCP was emphatically analyzed. 1 384 differentially expressed genes were found in pre-climacteric, includ- ing 1 067 up-regulated genes and 317 down-regulated genes; 346 differentially expressed genes in onset of climacteric, with 143 genes were up-regulated, and 203 genes were down-regulated. Only 288 differ- entially expressed genes were found between the fruits under 1-MCP treatment in pre-climacteric and in onset of climacteric. The clustering heat map analysis of the 288 genes included 124 genes were signifi- cantly down-regulated after 1-day treatment with 1-MCP, and164 genes were significantly up-regulated after 1-day treatment with 1-MCP. GO enrichment analysis have shown that the differential expression genes were mainly enriched in hormone synthesis and biological stress pathways. Transcription factor analysis has shown the genes mainly belong to WARK, ETR and ERF family. Functional annotation of unknown genes revealed that 11 out of 40 unknown genes were polypeptide, accounting for 27.5% of unknown genes. RT-PCR analysis found that the aging-related gene Prupe.4G214900 and ethylene-relat- ed gene Prupe.4G095400 were down- regulated after 1- MCP treatment, and the polypeptide genesPrupe.1G472800, Prupe.4G270100, Prupe.5G072500, Prupe.7G256100, and Prupe.5G059100 were up-regulated.【Conclusion】1-MCP treatment had distinct effects on ethylene release and softening pro- cess in pre- and onset climacteric peach fruits. Transcriptome analysis indicated that 1-MCP treatment affects differential gene expression depend on different development stage. In onset climacteric peach fruits, 1-MCP treatment induces the expression of genes related to ethylene and auxin signaling, and the genes may accerlate fruit softening process during postharvest storage. Furthermore, some new peptide genes were observed, which may play an important role in peach fruit ripening. These findings will pro- vide new insight for future study on postharvest preservation of peach fruits.