Rules And Regulation Of Sugar Metabolism And Lipid Accumulation Of Symplocos Paniculata

Symplocos paniculata,a member of Symplocos,Symplocaceae,is an deciduous shrub or small tree having ecological value.It’s a new oil plant,of whole fruit filled with oil.The flesh of the fruit is rich in fatty acids that differ from the seeds in composition,which is closely related to the yield and quality of whole-fruit oil.Plant oil is a high-energy storage material derived from the primary product of photosynthesis,sugar,and the ab initio synthesis of fatty acids and the assembly of triacylglycerols(TAG)are closely related to sugar accumulation and conversion.A comparative study of the dynamic changes of sugar and oil accumulation in the flesh and seeds of Symplocos paniculata and related regulatory genes would be beneficial to improve the quality of Symplocos paniculata oil and increase the oil content of Symplocos panicuflesh.In this study,the pulp and seeds(90 DAF,120 DAF and 140 DAF after pollination)were selected at different developmental stages,and transcriptomics was combined with conventional physicochemical analysis and high-throughput sequencing technology to analyze the dynamic changes of sucrose,starch and Carbohydrate metabolism-related enzyme activities and fatty acid contents in the pulp and seeds during fruit development,and to find out the differences between the pulp and seeds according to their different developmental stages.The key enzyme genes that influence the Carbohydrate metabolism of pulp and seeds on lipid synthesis were identified based on the differential expression of genes in different developmental periods.The main findings are as follows:(1)According to the Symplocos paniculata changes during the development of white Symplocos paniculata fruit,The accumulation of oil in both pulps and seeds tended to increase gradually,but the rapid accumulation of oil in pulps occurred during the slow fruit enlargement period(70 DAF to 100 DAF)and the over-ripening period(120 DAF to 140 DAF),while the rapid accumulation of oil in seeds occurred during the rapid fruit expansion period(10 DAF to 70 DAF)and the fruit color change period(100 DAF to 120 DAF);there were also significant differences in the dynamics and relative contents of sucrose and starch accumulation in flesh and seeds at different stages of fruit development.The oil content in the pulp was positively correlated with starch and sucrose at the rapid expansion and slow enlargement stages,and negatively correlated with sucrose at the color change stage,and positively correlated with sucrose at the over-ripening stage,while the opposite was true in the seeds.(2)The fatty acid fractions of fruit flesh and seeds differed in different developmental periods.The fatty acid fractions in the fruit pulp were mainly oleic acid and palmitic acid,which gradually increased with fruit development,while linoleic acid and other fatty acids were decreasing,and the saturated fatty acid content was ranged from 62%to 31%;the fatty acids in the seeds were mainly oleic acid and linoleic acid,with oleic acid increasing with fruit development,linoleic acid decreasing,palmitic acid basically unchanged,and the unsaturated fatty acid content remained at about 88%.(3)Sucrose synthesis-related enzymes(SPS,SSI)and sucrose catabolic enzymes(SUS)varied significantly in the flesh and seeds during different developmental stages of Symplocos paniculata fruits,and the differences in enzyme activities between the flesh and seeds were also significant.There was a stage-specific correlation between the activities of enzymes related to sugar metabolism and oil accumulation at different developmental stages.The accumulation of oil in the pulp and seeds was positively correlated with catabolic enzymes at the rapid expansion and color change stages,and was significantly correlated in the seeds,while the oil content in the pulp was highly correlated with sucrose synthase at the overripe stage.The differences in oil accumulation in pulp and seeds were mainly due to the differences in the activities of enzymes related to sugar metabolism in different periods.(4)The pulp and seed transcriptomes of Symplo cos paniculata were sequenced to obtain 7 444 281 036 high-quality clean reads,which were assembled into 124 923 nonredundant Unigene,of which 51.59%Unigene were annotated to the public database.Based on the KEGG database annotation,we identified key enzymes in the metabolic pathways of starch sucrose metabolism,glycolysis and gluconeogenesis,tricarboxylic acid cycle,and fatty acid biosynthesis,and elucidated the pathways between sugar accumulation metabolism and lipid accumulation in the pulp and seeds of Symplocos paniculata,and initially screened four differential genes for sugar metabolism related to lipid synthesis in the pulp and seeds of Symplocos paniculata(PGK3,PKP1,PDHE1,and MDH)and four differential genes for oil synthesis(FATB,HAD,KAR,and DGAT).In addition,malQ,LPAAT and PAP were key genes for oil accumulation in the pulp,FATB was more highly expressed in the pulp,and SUS and GPAT were key genes for oil accumulation in the seeds.In conclusion,this paper investgated and expounded the dynamic changes of sucrose starch content,enzyme activities related to glucose metabolism and fatty acid content in pulp and seeds of Symplocos paniculata fruit at different developmental stages.Based on the analysis of differential expression genes in pulp and seeds at different developmental stages,key enzyme genes in glucose metabolism pathway that play key role in regulating lipid synthesis in pulp and seeds were screened.Those provided the theoretical basis for breeding of high oil germplasm resources of Symplocos paniculata.