Comparison Of Chemical Composition Of Acorns In Quercus Variabilis And Quercus Mongolica And Deciphering The Polyphenol Metabolic Pathways During Acorn Development

With global climate change and population growth,it is becoming an increasing problem for the shortages of food supply.The fruits of Fagaceae have the potential to replace traditional food crops and can be developed as a new source of starch and functional food.Among them,acorns have the huge annual output in China,but the current utilization level is far behind.This study firstly compared and analyzed acorn traits from the different provenances of Quercus variabilis and Q.Mongolica in the genus of Quercus.Secondly,the dynamic changes of polyphenol contents in different tissues of Q.variabilis in the different periods were analyzed,and then the polyphenol metabolic pathways were foucused on deciphering in the cupules and kernels,respectively,during the development of acorns by the RNA-seq.The main results were as follows:(1)The acorn traits of Q.mongolica and Q.variabilis collected from the different provenances had significant differences.There was a certain correlation between acorn sizes,polyphenol contents and geographic locations.As the latitude increases,the acorn sizes increased and the polyphenol contents decreased.Acorns of Q.mongolica in North China and Q.variabilis in the Southwest China had higher starch and total polyphenol contents.Totally,the total polyphenol contents in the acorns of Q.variabilis,which has a larger distribution range,were significantly higher than those of Q.mongolica.(2)The free phenol contents were significantly higher than the bound phenol contents in all the measured tissues of Q.variabilis.During the development of acorns,the polyphenol contents in the cupules were higher than those in other tissues.The polyphenol contents in the cupules and peels showed a declining trend,while they firstly increased and then decreased in the kernels,but they changed slightly in the barks of one-year branches and leaves.The polyphenol content in each tissue was positivly correlated to the total antioxidant capacity,and the effective antioxidant components in the kernels accounted for a relatively higher proportion.(3)The cupules and kernels of Q.variabilis were used to investigate the differential expression genes(DEGs)during the development of acorns by RNA-seq.Among the six developmental time points in the cupules,the numbers of DEGs in two adjacent time points were 134,687,610,1028,and 179.Among four developmental time points in the kernels,and the numbers of DEGs in two adjacent time points were 1251,373,1247,and 538.Bioinformatics analysis showed that there were significant differences in the gene expression profiles,which were the tissue-specific and time-specific,in the cupules and kernels of acorns at the different developmental stages.The enrichment analysis by GO and KEGG showed that DEGs in the acorns were mainly enriched in metabolic pathways and the biosynthesis of secondary metabolites.The phenylpropane and flavonoid biosynthesis genes in the cupules were mainly enriched in the middle and later stages of acorn development,while DEGs in the kernels were mainly enriched in the early and later stages,which was consistent with the change trend of polyphenol contents.WGCNA analysis identified a total of 30 modules,and one was significantly positively correlated with the content of polyphenols.The GO enrichment analysis of the module showed that the synthesis process of aromatic and cyclic compounds related to polyphenols were mainly enriched and 15 genes may be mainly involved in the metabolic pathway of polyphenols in the acorn development of Q.variabilis.During the acorn development,83 transcripts of 12 gene families were found to be involved in the phenylpropane biosynthetic pathway,and 31 transcripts of 11 gene families were involved in the biosynthetic pathways of flavonoids and anthocyanins.In summary,the traits of acorns from different provenances were systematically evaluated,and the mechanism of polyphenol accumulation was firstly revealed in this study,which would lay the foundation for subsequent selection and breeding of fruit resources in Fagaceae,and in-depth research on regulating the fruit traits related genes and improving the utilization of acorns.