Accumulation And Transcriptional Regulation Of Norisoprenoids In Wine Grapes

Norisoprenoids are the important components constituting grape varietal aroma.Norisoprenoid compounds make a great contribution to aroma quality of grapes and wines owing to their extremely low perception threshold and pleasant floral fruit characteristics.The concentration varies with cultivations,meteorological factors and grape varieties.Recently,a series of studies about the components and content of norisoprenoid has been reported,and the key genes responsible for norisoprenoid biosynthesis had been biochemically characterized in grapes,but the study on the accumulation and its transcriptional regulation were not identified yet.Some problems remain to be resolved.How does climatic factors and cultivation management affect the accumulation and gene expression of volatiles during grape berry development?Whether there are difference in the content of norisoprenoid and its gene expression pattern among different varieties?And how about the transcriptional regulation of these genes?In this study,we compared the difference between rain-shelter and open-field cultivation on volatile compounds,in order to investigate the influence of microclimate alteration on the accumulation of norisoprenoids and gene expression.The comparsion of different varieties on norisoprenoids accumulation and gene expression was also used to explore the genetic factors.The response of key gene promoters to abiotic factors was investigated,to reveal the biosynthesis of norisoprenoid and its transcriptional regulation in wine grapes preliminarily.The results were as follows:The rain-shelter cultivation significantly reduced the total solar radiation,photosynthetically active radiation and ultraviolet radiation reaching to the clusters.Compared with open-field cultivation,rain-shelter cultivation signigicantly enhanced the synthesis of free straight-chain aliphatic aldehydes,acids and esters,but led to a decrease in the accumulation of free straight-chain aliphatic alcohols.The levels of amino acid-derived benzenoids were significantly increased in the grapes under rain-shelter cultivation,but showed lower levels of bound acid-derived branched-chain aliphatics.Rain-shelter cultivation caused an increase in free isoprene-derived volatiles and a reduction in bound isoprene-derived terpenes and norisoprenoids.These results suggested that rain-shelter cultivation modifies carbon allocation in the volatile metabolism.The PCA analysis indicated that compared with cultivation treatment,vintage had a much greater impact on the accumulation of volatile compounds.The longer sunshine hours and more effective accumulative temperature in berry maturation phase,compared with 2013 vintage,might be a reason for the higher levels of most of the volatiles synthesized in the 2012 vintage grapes.The expression of norisporenoid metabolism related genes were examined.The 2012 vintage grapes under the rain-shelter treatment exhibited a higher transcript abundance of VvPSY but a lower level of VvCCDl,howerver,no significant difference were found in the 2013 vintage grapes.The comparison of norisoprenoids was studied among different varieties:muscat-type 'Muscat blanc a Petit grain' and 'Tchervine Muscat',aroma-type 'Gewiirztraminer' and non aroma-type'Chardonnay'.The total concentration of the norisoprenoid volatiles first increased and then decreased with grape development and the highest concentration was observed before veraison.No difference was found on the types of norisoprenoid compounds,but significant difference were obtained in the concentration of norisoprenoids,and the muscat grapes showed the highest content.The expression of VvCCD4a and VvCCD4b in mature grapes paralleled with the accumulation of norisoprenoids.The region and vintage also had an effect on the accumulation of metabolic products.'Muscat blanc a Petit grain' grapes in Changli region showed higer levels,and the content of norisoprenoid compounds in 2011 vintage were significantly higher than that in 2010.Single nucleotide polymorphisms(SNP)were found from the nucleotide sequence of VvCCD1,VvCCD4a and VvCCD4b in the four different grape varieties.And 5,3,6 anino acids mutations,respectively,in amino acids sequence were found in the three genes.These mutations may be the reason causing the differential expression of the related genes and the production of norisoprenoids among grape varieties.To further investigate the transcriptional level of genes realted to norisoprenoids metabolism,we cloned the promoters of VvPSY,VvCCD1,VvCCD4a,VvCCD4b from 'Cabernet Sauvignon' grapes.The expression of VvPSY,VvCCD1,VvCCD4a,VvCCD4b gene promoters in Arabidopsis thaliana leaves showed that the activity of VvPSY promoter was enhanced by 1 mM ABA,and shading of light,higher temperature,strong light were in the contrast.VvCCDl,VvCCD4a,VvCCD4b promoters can be activated by high temperature,strong light and ABA induction,which subsequently up-regulates the expression of GUS;while shading of light could reduce the activity of these promoters.Based on these findings,it is inferred that the transcriptional regulation of VvPSY,VvCCD1,VvCCD4a,VvCCD4b genes should be involved in the response of cis-elements on this gene promoter to external stimuli.