Effects of 1-MCP on the genes related to wax anabolism in pear peel based on transcriptomics

【Objective】According to the investigation and laboratory research of our study group for several years, it has been found that the main pear cultivar Yuluxiang was easy to become greasy in the early stage of shelf life at room temperature, and also in the middle and late stage of cold storage. Previous researchers have reported that the expression levels of genes related to wax anabolism in the peel and ethylene synthesis are related closely to the degree of oiliness in the peel. Moreover, the inhibitive effect of 1-MCP on ethylene release has been widely reported, and thus the regulation mode of 1-MCP on the wax synthesis and metabolism genes in pear peel during shelf life at room temperature was studied, which provided a theoretical basis for a preliminary exploration of the molecular mechanism of 1-MCP regulation of pear peel greasiness.【Methods】Yuluxiang pear was used as the experimental material，and fruits with uniform size and without pests, diseases and bumps were selected as experimental samples, which were fumigated with 1.0 μL·L-1 1-MCP for 24 h, and the untreated fruit was used as the control. Then, the appearance changes of the fruit were observed on the shelf at 20 ℃ for 14 days. At the same time, the fruit surface brightness L value was detected. RNA was extracted from frozen peel samples every 7 days for transcriptome sequencing and data analysis, and RT-qPCR technology was used to verify the significant difference genes.【Results】During the whole shelf life, the appearance quality of fruit treated with 1-MCP was better than that of the control. On the 14th day of shelf life, it could still maintain a better green fruit surface, and a lower L value of fruit surface brightness, and there was no greasy phenomenon on the fruit surface at this time. Through transcriptome sequencing and data analysis, a total of 103283229900 clean reads were obtained, and the data quality was high. The results of reference genome alignment showed that the sequencing data of the Yuluxiang fruit peel were well aligned with the pear reference genome. Compared with the control, there were 2463 differentially expressed genes up-regulated and 599 differentially expressed genes down-regulated in the 1-MCP group on the 7th day of shelf life. On the 14th day of shelf life, there were 786 differentially expressed genes up-regulated and 284 differentially expressed genes down-regulated in the 1-MCP group. The number of differentially expressed genes in two groups was the highest on the 7th day of shelf life, indicating that the difference between the two groups was large. Therefore, the significant differential genes of two groups of fruits on the 7th day of shelf life were enriched into the lipid metabolism pathway through KEGG, a total of 95 significant differential genes, and 13 secondary lipid metabolism pathways were enriched into this pathway. The secondary metabolic pathways directly related to wax biosynthesis were biosynthesis of cutin, suberine, wax, fatty acid elongation, fatty acid biosynthesis and fatty acid degradation. In this study, a total of 7 significantly different genes (PyKCS1, PyKCS20, PyKCR1, PyPLDALPHA4, PyLACS9, PyFAD2 and PyCER1) were enriched in lipid metabolism pathways, which were involved in lipid secondary metabolic pathways such as fatty acid extension, synthesis and degradation, and PyKCS20, PyKCR1, PyPLDALPHA4, PyLACS9, PyFAD2 and PyCER1 were down-regulated and PyKCS1 was upregulated in the 1-MCP-treated group. The results of RT-qPCR showed that 1-MCP treatment significantly inhibited the up- regulated expression of PyLACS9, PyKCS20 and PyCER1 genes during the whole shelf life, and inhibited the up-regulated expression of PyPLDALPHA4 and PyFAD2 genes in the first 7 days of shelf life, which verified the regulation of 1-MCP on the expression pattern of wax anabolism genes in the peel of Yuluxiang pear. The results of correlation analysis showed that PyLACS9 was significantly and positively correlated with the L value of fruit surface brightness (p ＜ 0.05), and the L value was strongly positively correlated with PyKCS20, strongly negatively correlated with PyPLDALPHA4 and PyACS-1, negatively correlated with PyKCS1, and weakly correlated with PyKCR1, PyCER1 and PyACO2, but not significantly (p ≥ 0.05). In addition, the correlation between different differential genes showed that LACS9 was strongly negatively correlated with PyACS- 1, PyKCR1 and PyCER1 were strongly positively correlated with PyACO2, PyPLDALPHA4 was strongly positively correlated with PyACS-1, PyFAD2 was strongly positively correlated with PyACO2 and PyACS-1, and they were not significant (p ≥ 0.05), so it was speculated that PyLACS9 may be the key gene leading to the greasiness of Yuluxiang fruit peel.【Conclusion】In summary, 1-MCP treatment could maintain the good appearance quality and low L value of Yuluxiang fruit during shelf life at room temperature, which may affect the greasiness of peel by affecting the expression level of wax anabolism genes in Yuluxiang fruit peel. Exploring the regulatory effect of 1-MCP on the waxy synthesis and metabolism genes in the peel of Yuluxiang pear during shelf life provides a theoretical basis for the prevention and control of post-harvest greasiness of pear fruit.