Preliminary Study On The Changes Of Main Nutrients And Metabolic Mechanism During The Fruit Development In ‘Donghong' Kiwifruit

Kiwifruit has extremely high nutritional vallue,which is rich in Vc,phenolic compounds,amino acids,mineral composition and dietary fiber.In recent years,due to its unique flavor and nutritional value,red-flesh kiwifruit has become more and more popular among consumers.But the comprehensive evaluation and metabolic mechanism of nutrients in red-flesh kiwifruit is far from conclusive.In present study,we used high-performance liquid chromatography?HPLC?analyzed the changes of sugars,starch,organic acids and phenolic compouds in a new red-fleshed kiwifruit cultivar‘Donghong'during fruit development,and adopted transcriptome sequencing?RNA-Seq?and realtime fluorescence quantitative PCR?qRT-PCR?technologies to screen the key genes related to sugars,starch,organic acids and phenolic compouds metabolism,to lay basis for the evaluation and metabolic mechanism of nutrients in kiwifruit.The main results are as follws:?1?In the fruit of‘Donghong',epicatechin?flavanols?and chlorogenic acid?phenolic acids?were the main phenolic compounds,and the content was 15.33,7.01 mg·g^-1FW.The second were quercetin?flavonols?and protocatechoic acid?phenolic acids?.The content of phenolic acids:caffeic acid,p-coumaric acid and ferulic acid were low.Epicatechin content increased first and then decreased;Chlorogenic acid rose during the late stage;The other phenolic compounds content all peaked at the ovary stage,and then decreased with fruit development.Transcriptome data analysis found that most of the genes located upstream of phenolic compounds synthesis were down-regulated at fruit ripening,including AcPAL,Ac4CL,AcC4H,AcCHS,AcCHI,AcF3H,which affected the major phenolic compounds synthesis.?2?Cyanidin 3-O-[2-O-??-xylosyl?-?-galactoside]?Cy-xyl.gal.?and cyanidin3-O-?-glucoside?Cy-gal.?were important anthocyanins.The anthocyanins content both peaked at the ovary stage,and the ovary was red.As 0-60 days after full bloom?DAFB?,the anthocyanins contents decreased sharply and the red in fruit disappeared.With the fruit development and maturity?90-150 DAFB?,the anthocyanins content increased drastically and the fruit appeared red again.The differentially expressed genes analysis showed that,the AcLDOX2 expression level was positively correlated with anthocyanin content and was a key gene on regulating anthocyanin synthesis;The anthocyanin glycosylation and acylation genes Ac5GGT and Ac5AT played important roles in the anthocyanin modification and stability during the late fruit development.Transcription factor AcMYB4-1 might negatively regulate anthocyanin synthesis,while AcMYB10 regulated anthocyanin content during the late development stage.AcbHLH137 and AcbHLH74-2 had positive regulation on anthocyanin biosynthesis and accumulation.?3?At 0-60 DAFB and 90-150 DAFB,the soluble sugar content increased rapidly,and the change of content was not obvious at 60-90 DAFB.With the fruit development,the starch content accumulated gradually.The change of content was not obvious.The sugars content was fructose?glucose?sucrose.The fructose content and sucrose content increased by 4.21,10.04 times when the fruit ripenning.The glucose content generally showed an upward trend,which decreased at 0-60 DAFB.The expression level of sucrose synthesis genes AcSPS2,AcSPS3,AcSPP,AcSuSy1,AcSuSy3 and AcSuSy4 were up-regulated during the fruit development,which were key genes of sucrose synthesis and accumulation.The expression of AcINV2 peaked at 60 DAFB,which was due to the accumulation of fructose and glucose.The starch synthesis genes AcSBE1 and AcGPT expressed at a high level,which was the reason why starch continued to accumulate.?4?Citric acid and malic acid were mainly organic acids,followed by tartaric acid.Before 60 days,the citric acid content remained at a low level,and rose significantly to13.71 mg·g^-1FW at 90 DAFB and remained until the fruit matured.Malic acid content increased obviously at 0-60 DAFB and 90-150 DAFB,and then decreased quikly with the fruit development.The tartaric acid increased at 30 DAFB,and then decreased notably.On the whole,the other organic acids content decreased with the fruit development.At 0-60DAFB and 90-150 DAFB,the expression level of malate dehydrogenase genes AcMDH1and AcMDH2 down-regulated,and up-regulated at 60-90 DAFB,which negatively correlated with malic acid content,indicating that they negatively regulated the malic acid synthesis.While the expression level of citrate synthase gene AcCS1 was up-regulated significantly,resulting in an increase in citrate content.