Screening Of Key Enzyme Genes Related To Sugar Metabolism In Different Litchi Cultivars

The intrinsic quality of fruit depends largely on the type and quantity of sugar.Sugar is not only an important factor affecting the quality of fruit,but also a signal molecule,which is involved in the regulation of the development and the quality formation of fruit.Litchi(Litchi chinensis Sonn.),a kind of evergreen fruit tree widely cultivated in subtropical region of south China,has abundant germplasm resources and high edible value and nutritional value.The edible part of litchi is aril,which has high content soluble sugar mainly existing in the form of sucrose,glucose and fructose.But there are distinctly differences in the component and content of sugar among different cultivars.So far,it is not clear the reasons of the difference of sugar accumulation in different cultivars of litchi.We measured the sugar content of 24 kinds of mature litchi,and divided them into three categories according to the previous studies.Finally,three cultivars with typical sugar accumulation patterns,‘FZX',‘HXC' and ‘WHL' were selected for further study.Comparing the sugar accumulation patterns of three litchi cultivars in developmental aril and screening the key genes related to sugar metabolism,genes encoding INV,INH,SS,SPS,FRK were cloned and analyzed.Comparing the coding region sequence of LcVIN1 among different litchi cultivars,we tried to find the difference..The purpose of this study is to elucidate the molecular mechanism of sugar accumulation difference among different litchi cultivars.The main results are as follows:(1)According to the result of sugar content detection,we assured the diversity of sugar accumulation in mature stage among 24 different cultivars.Eight cultivars belong to sucrose accumulation type,such as ‘ZW055',‘NMC' and ‘WHL';8 cultivars belong to middle type,such as ‘GW',‘MS151' and ‘HXC';8 cultivars belong to hexose accumulation type,such as ‘FHGW',‘Kom',‘HY' and ‘FZX'.(2)With the determination of the composition and content of sugar in the development stage of litchi,we discovered that the sugar accumulation pattern in ‘FZX'?‘HXC' and ‘WHL'.Sucrose accumulation cycle and content of ‘WHL' and ‘HXC' are much higher than that in ‘FZX',whereas the content of hexose accumulation is lower than that in‘FZX'.Sucrose accumulation of ‘WHL' and ‘HXC' are consistent,however,hexose accumulation in 'HXC' is still on the rise in the late development stage,and 'WHL' has almost stopped.(3)Thirty-four gene involved in sugar metabolism were obtained from litchi aril using RT-PCR.Through sequence analysis and cluster analysis,the genetic structure,conservative domain and phylogenetic trees were obtained,which provide a reference for the screening of key enzyme genes in litchi sugar metabolism..(4)Real-time PCR analysis combined with sugar content analysis and bio-information analysis showed that LcVIN1,LcINH1,LcINH2 and LcSPS1 might be the key genes responsible for the sugar accumulation of different litchi cultivars.(5)To investigate whether coding sequences differences exist among cultivars,we cloned the LcVIN1 from aril cDNA of ‘FZX',‘HXC' and ‘WHL',and found there was no absence or variation of large segments in LcVIN1.Just a bit of SNPs were discovered.This result indicated that the LcVIN1 appeared not to be the key factors contributed to the diversity of sugar accumulations in different litchi cultivars.