| Orient melon(Cucumis melo var.makuwa Makino)has a long planting history in China and is a very important cash crop.It has a large planting area in Heilongjiang Province.Sweetness is one of the important factors affecting its commercialization.In order to find out the reasons for the sweetness difference of thin skinned melon fruit,the inbred lines "DX108" and "DX3-5" with obvious sweetness difference were used as materials to study the sugar content,the activity of enzymes related to sugar metabolism and the correlation between source and sink during fruit development;At the same time,the regulation mechanism of glucose metabolism during fruit development and maturation was studied by combining transcriptome and metabolome.The results was as follows:1.The sugar content of orient melon fruits,DX108 and DX3-5,at different post-anthesis stages was determined,and it was found that the sugar content in fruits of DX108 at different development stages was higher than that of Dx3-5.Therefore,DX108 was identified as high sugar type,and DX3-5 belonged to low sugar type.Metabolomics analysis of fruits on DX108 and DX3-5at 30 days after flowering showed that the main differential sugar in mature fruits betweet DX108 and DX3-5was sucrose,and it is speculated that the difference of sucrose content in fruits determines the difference of sweetness between DX108 and Dx3-5.2.In DX108 fruits,the higher activities of sucrose synthase(SS)-synthesis direction,sucrose phosphate synthase(SPS)and low sucrose synthase(SS)-decomposition direction coordinated the accumulation of high sucrose,fructose and glucose.However,the activities of SPS,acid invertase,neutral invertase and sucrose synthase(SS)-synthetase affected the accumulation of sucrose,fructose and glucose in DX3-5 fruit,which resulted in the difference of sugar content among varieties.3.The source-sink correlation analysis showed that the contents of stachyose and raffinlose in the front leaves of DX3-5 were prominently higher than those of DX108,while there was no significant difference in sucrose content during 10-20 days of fruit development,suggesting that the ’source’ of DX3-5 was larger than that of DX108.The effect of stachyose and raffinose on fruit growth of DX3-5 was greater than that of DX108.After 20 days of fruit development,sucrose in leaves of DX3-5mainly promoted fruit growth,while raffinose and sucrose in leaves of DX108 promoted fruit development.At the same time,it was found that the single fruit weight and yield per plant of DX3-5 were higher than that of DX108,while the contents of sucrose and starch in DX3-5 were obviously lower than that of DX108.It was speculated that the carbohydrate in DX3-5 may mainly promote the fruit growth,while the carbohydrate in DX108 could also be converted into sugar and starch while promoting fruit growth,resulting in differences in fruit yield,sugar content and sweetness.4.Transcriptomic sequencing analysis of DX108 and DX3-5 fruits at 10,20 and30 d after anthesis showed that the total number of Clean Reads in each period was43.27,40.39 and 38.59 Gb,and 2981,5810 and 4396 differency-expressed genes in each period,respectively.According to GO analysis and KEGG enrichment analysis,486,209 and 592 differentially expressed genes related to glucose metabolism were screened from the transcriptome data of fruits at 10,20 and 30 d after anthesis,respectively.5.Correlation analysis was performed based on the sugar content,metabolic enzyme activities and expression levels of differential genes related to sugar metabolism.Ten genes related to fruit sugar metabolism,four sugar transporters(including two hexosaccharide transporters and two SWEET)and 11 transcription factors from different families(including 1 MYB,2 b ZIP,3 WRKY,2 ERF,2 NAC and 1 ZAT)were screened from differentially expressed genes.Thereinto,there were3 sucrose synthase genes(2 directase genes and 1 directase gene),2 sucrose phosphate synthase genes,1 hexokinase gene,2 invertase genes and 2 fructokinase genes. |
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