The Effect Of Genes For Sucrose Metabolism And Transportion On Fruit Sugar Accumulation In Strawberry (Fragaria×Ananassa Duch.)

Sugar is not only an energy substance involved in plant growth,development and morphogenesis but also plays a role as signaling molecules in response to environmental stress,regulation of plant growth and development and formation of fruit quality.Strawberry is one of the most famous berries in the world.The accumulation of sugar in strawberry has an important influence on the fruit quality.In this study,the correlation between sugar metabolism and transport related genes and sugar content,composition and activities of sugar metabolism enzymes,the evolution and expression of the genes and the responses to a variety of hormones,exogenous sugars and pathogenic fungi were studied in two cultivars.Main results were as following:a.The soluble sugars in strawberry fruits were composed of glucose,fructose and sucrose which played a dominant role in sucrose accumulation.Organic acids in strawberry contained citric acid and malic acid,and contents of citric acid was 3-4 times higher than that of malic acid.The content of sucrose in strawberry fruit was significantly negative correlated with the activity of alkaline/neutral invertase during fruit development in both two cultivars.b.The alkaline/neutral invertase gene family of strawberry was composed of a total of 8 members,and 4 members(Fa.A/N-Inv A,Fa.A/N-Inv B,Fa.A/N-Inv C,Fa.A/N-Inv E)of this family were detected at RNA level.c.Fa.A/N-Invs were expressed in root,stem,flower,receptacle and achenes,prominently in the mature leaves,which suggested that A/N-Inv participated in many developmental processes in strawberry.The dynamic changes of A/N-Inv enzymatic activity were consistent with the patterns of Fa.A/N-Invs transcripts during fruit development.It indicated that the transcriptional regulation of A/N-Invs played a prominent role in the quality of strawberry fruits.d.Fa.A/N-Invs could respond to external application of IAA,GA and 6-BA at transcriptional level.As substrate and product of A/N-Inv enzymatic reaction,sucrose and glucose could promote or inhibite the expression of Fa.A/N-Invs,respectively.Turanose,a sucrose analogue,also could induce the expression of Fa.A/N-Invs.These results indicated that Fa.A/N-Invs in strawberry were involved in several hormonal and sugar related signaling pathways underlying multiple biological processes.e.Transcription of A/N-Inv genes could respond to the inoculation of C.fructicola.Two members Fa.A/N-Inv B and Fa.A/N-Inv E were most sensitive to and quickly repressed by this hemibiotrophic pathogen.It suggested that the A/N-Inv could participate in the defense response of strawberry to the pathogenic fungi by affecting carbohydrate distribution.f.Sucrose rapidly increased from white fruit in ?Benihoppe?,but sucrose accumulation in ?Shen Yang? was slow.The content of sucrose in ripe ?Benihoppe? fruit(50.7mg·g-1FW)was double of that in ?Shen Yang? fruit(23.2 mg·g-1 FW).Quantitative and semi-quantitative PCR were used to study the expression patterns of SUT family genes.The expression levels of Fa SUT1-2,Fa SUT6-7 were relatively higher in ?Benihoppe? fruits than in ?Shen yang? fruits from green stage to ripening stage.Notably,transcripts of these SUT genes were detected in ?Benihoppe? while not in ?Shen Yang? fruits.This difference in SUT expression contributed to the differential accumulation of sucrose in ripe fruits of two cultivars.This study showed that strawberry alkaline/neutral invertase promoted the redistribution of carbohydrates and affected fruit development through the decomposition of the photosynthetic products in green fruit stage.The fruit sugar began to accumulate quickly with alkaline/neutral invertase activity decreased in white fruit stage.With net activity of sucrose-metabolizing enzymes tending to zero,accumulation of SUT family genes transcripts were up-regulated to regulate sucrose input and promote sucrose accumulation in the ripping fruit stage.