Studies On The Difference About Starch Content And Gene Relative Expression Of The Key Enzymes In Ipomoea Batatas L.

Sweetpotato [Ipomoea batatas L.] is one of the most important food,feed and industrial raw materials crops in the world,with highly using deficiency of light,calorie,water and high yield of biomass per unit area,producing large amount of starch.Enriching starches in storage roots of sweetpotato,the studies of sweetpotato starch metabolic pathway play an important role in improving the yield and quality of starch in storage roots of sweetpotat.The changes of starch content in roots of 6 sweet potato varieties and the expression level of 8 key enzyme genes in starch metabolism of sweetpotato were studied at 4 time points after transplanting in the field.,in order to find out the key enzyme genes which were more directly related to starch synthesis and degradation.these studies would provide theoretical basis for the further exploring about molecular mechanism of starch accumulation and further deepening of breeding of starch sweetpotato varieties.The main results in present paper are as follows:1.Analysis of variance showed that there were significant differences in storage roots starch contents between varieties and their growing period.The starch contents in fresh storage roots during their growing period showed a tendency of increasing in the early growing stage and decreasing in late stage.The starch contents of 6 sweetpotato varieties changed from 6.21% to 29.02% among four time points.Yushu No.27 have the highest average starch contents 24.79% among 6 varieties during the whole growing period.The average starch contents of 6 varieties at the 120 th day have the highest contents 21.39% among 4 time points.The maximum extent of changes in the starch content of six varieties during their growing period was from 60 days to 90 days with an average increasing of 58.23%.Yushu No.27 and Yushu No.1 are high-starch content varieties,Yusu No.8,Yushu No.99 and Yusu No.303 are mid-starch content varieties,Chaoshu No.1 is low-starch content variety.2.Real time fluorescence quantitative PCR analysis shows,Changes in relative expression of starch metabolism key enzyme genes in tuber root during growth periodhave differences between genes and varieties.The change pattern of relative expression levels of key enzymes involved in the starch metabolism of storage roots during their growing period included 4 change patterns,namely earlier stage higher expression,later stage higher expression,stable expression,and large fluctuating expression,and among them,the proportion of the key enzyme genes that belong to the earlier stage higher expression type is the highest.The change patterns of relative expression levels of the gene of the key enzymes are different in different varieties.Among them,there are a large number of pre-expression genes in Yushu No.1,Yushu No.27,and Yusu No.8belong to high-starch content varietiesbe.Synchronous earlier stage higher expression of those synthetise and degradation genes is beneficial to starch accumulationand,and the earlier stage higher expression of ?-amylase,?-amylase without any earlier stage higher expression of synthetise gene is an important factor about lower starch content.3.Correlation analysis shows that there are different synergistic effects between relative expression levels of genes of key enzymes involved in starch metabolism.The correlation analysis showed that the metabolic genes of key enzymes have synergistic effects during the starch synthesis and degradation,and this synergy effect comes at the cost of time.and appears at some key time in some varieties.AGPa,AGPb,GBSSI,SBEII,and SS are significantly correlated with the relative expression of the key genes for starch synthesis during the growth period.with more obvious synergistic effects.AGPa and AGPb,as important upstream expression genes,have more synergistic effects with many downstream synthetic genes(e.g.GBSSI,SBEII and SS,etc.),affect the expression of these downstream genes,and play an important role in the initiation of starch synthesis,GBSSI and AGPa have the most obvious positive synergy among medium and high starch content varieties,the positive synergy of SBEII with AGPb,GBSSI,and SBEI in medium and low starch varieties is most obvious,however,SS exhibited significant positive synergy with the corresponding AGPb and GBSSI in the high-starch varieties.The expression of a-amylase is relatively inactive,the correlation coefficient between ?-amylase and GBSSI is the largest among the low starch varieties,the active expression of ?-amylase may be one of the important factors in the starch degradation.At each growing point,there are fewer pairs of genes with significant correlation,and the lowest at 165 d,which indicated that the cooperation between genes would take time cost to be effective.At 60 d and 90 d,Yushu No.99 and high starch cultivar Yushu No.27 showed significant correlation with more gene pairs,suggesting that the correlation between the genes has a critical period effect.4.The correlationships between the relative expression levels of 8 genes of key enzymes involved in starch metabolism and the starch content of fresh storage roots were not significant.At 60 days after transplanting,the relative expression of 6 key enzyme genes for starch synthesis were positively correlated with fresh starch content.At 90 days and 120 days,the relative expression of 6 key enzyme genes for starch synthesis were negatively correlated with fresh starch content because that the general variation trend of starch content during their growing is lower in the early stage and higher in the late stage.Conclusion: There are significant differences in the starch contents in fresh storage roots of sweetpotato between varieties and during their growing.AGPa and AGPb,as important upstream expression genes,play an important role in the initiation of starch synthesis,GBSSI,SBEII,and SS are important starch synthesis genes.The change patterns of relative expression levels of the key genes involved in starch metabolism during their growing were different in different varieties and in different genes.There are synergistic effects which are more important to increase starch content during the growth period and the critical period.Synchronous earlier stage higher expression of those synthetise and degradation genes is beneficial to starch accumulationand,and the earlier stage higher expression of ?-amylase,?-amylase without any earlier stage higher expression of synthetise gene is an important factor about lower starch content.