Transcriptome-based Study On The Mechanism Of High Concentration CO₂ Inducing Acetaldehyde Metabolism In Persimmon Fruit

The astringent type persimmon（Diospyros kaki Thunb.）fruits continue to accumulate tannins during the growth and development process,resulting in astringent taste after the fruit matures.High-concentration CO₂ has been proved to be the most effective method for de-astringent.However,this treatment shows different effects among different cultivars,and its inherent molecular mechanism is still unclear.The astringency of persimmon fruit is mainly caused by soluble tannins,and the high concentration of CO₂ has been shown to induce acetaldehyde metabolism,which promotes the combination of acetaldehyde with soluble tannins to achieve de-astringency.In order to further explore the molecular mechanism of de-astringent,this study started with the endogenous acetaldehyde metabolism of fruits,and studied the relationship between the transcriptome data of persimmon fruit and carbohydrate metabolism and acetaldehyde production in the three cultivars of‘Laopige’（LPG）,‘Shijiazhuanglianhuashi’（SJZLHS）and‘Luoyangfangtianshengshi’（LYFTSS）.The main results are as follows:1.The overview of differences in acetaldehyde content and the transcriptome data of different cultivar fruits.The content of acetaldehyde and ethanol in fruits was determined,and it was found that the acetaldehyde and ethanol content of SJZLHS and LYFTSS were higher than that of LPG,and acetaldehyde could not be detected in LPG fruits.Through transcriptome data analysis,the results showed that the functions of differentially expressed genes in SJZLHS and LYFTSS fruits are not the same as those of LPG,and the number of genes upregulated by high concentrations of CO₂（95%CO₂）in SJZLHS and LYFTSS is higher than that in LPG.The above results,from the physiological and transcription levels,indicate that the response of LPG to high-concentration CO₂ treatment is weaker than that of SJZLHS and LYFTSS.2.Weighted gene co-expression network analysis（WGCNA）and carbohydrate metabolism analysis of the transcriptome.A gene module was screened by WGCNA,and its expression trend was significantly correlated with the content of acetaldehyde and ethanol（P<0.001）.The comparative analysis of the differentially expressed genes of carbohydrate metabolism pathway in different cultivars showed that the expression of structural genes in the acetaldehyde pathway was positively correlated with the content of acetaldehyde.The determination of precursor substances of carbohydrate metabolism showed that in addition to malic acid,sucrose,glucose and fructose showed small differences between cultivars,and the content of malic acid was too low to make the difference of acetaldehyde.The determination of the intermediate products of carbohydrate metabolism showed that the metabolites of phosphofructokinase increased significantly in SJZLHS and LYFTSS,and other intermediate metabolites increased significantly in LYFTSS.This result indicates that the differences in acetaldehyde between different cultivars may be caused by intermediate products of carbohydrate metabolism and gene expression.3.Using different cultivars to verify the relationship between carbohydrate metabolism genes and acetaldehyde content.On the basis of the 3 varieties previously studied,the fruits of another 14 astringent persimmon varieties were further collected,namely‘Meixianhengqumanaitou’,‘Xingtaitaishi’,‘Lichengmianshi’,‘Mianrangshi’,‘Yunyangwaguanshi’,‘Shigoushi’,‘Guyishi’,‘Huxianhuoguanshi’,‘Jishi’,‘Sanyuanshaoshi’,Xiaoheshi’,‘Jishanhanxin’,‘Ernizi’,‘Lintongbanshi’.After high-concentration CO₂ treatment,the acetaldehyde content of these fruits also showed a big difference（30.4-255.5μg/g FW）.The expression of 9 acetaldehyde metabolism candidate genes in different varieties was further analyzed,and the correlation between gene expression and acetaldehyde content was analyzed.The results showed that DkPFK1 in carbohydrate metabolism has the highest correlation with the content of acetaldehyde in fruits of different cultivars.In summary,through the analysis of transcriptome and material metabolism difference data,it is believed that the differentially expressed genes related to carbohydrate metabolism（especially PFK）are one of the molecular basis for the differences in acetaldehyde among different persimmon varieties.