The Primary Mapping Of Ascorbic Acid Hyperaccumulation Key Gene In Actinidia Erientha

The whole Actinidia genus contains higher levels of ascorbic acid（AsA）than other common fruits.And the AsA content levels varied significantly among different Actinidia genus plants.This peculiar biological phenomenon continues to receive scientific attention.But the molecular mechanism of AsA hyperaccumulation is not yet clarified.Firstly,we optimized AsA-measuring method.The best way was to grind 1 g fruit flesh with HCl O₄.Then the supernatant was diluted to 2ml,from which 666μl was used to mix with 570μl Na₂CO₃ of 1.25M.Then absorbance at 265nm was used to calculate AsA concentration.Then we detected the content of ASA and TAA in different kiwifruit species,and found that the contents of ASA and TAA in A.chinensis were 10 times lower than that in A.erientha.Hence,we chose A.eriantha“White”as maternal material,A.Chinensis“0809”as paternal material to construct a F1 hybridization population.From the population,325 plants were randomly selected to detect their leaf AsA contents.The AsA levels of the population,displaying a separation,distributed evenly within a range of 0-100 mg/100 g fresh weight.40 plants with either extremely high or extremely low AsA levels were selected to construct high or low extreme-pool.Through bulk segregant analysis-sequencing（BSA-seq）,we were able to locate the AsA hyperaccumulation key gene to a fragment of 1.59M on A.eriantha No.10 chromosome.Then we investigated the trends of AsA level changes in the whole fruit development of“White”and“Hongyang”（A.Chinensis）,founding that they showed similar patterns of level fluctuations.They both quickly accumulated AsA to a peak level in a relatively short period of time after inflorescence and then dropped to about half of the peak level.We selected the fruits of AsA rapid accumulation period,platform period and rapid decline period for“White”and“Hongyang”to perform transcriptome analysis.76 genes for“White”and 25 genes for“Hongyang”,respectively,were found to have different intergroup expression levels.Further analysis with the weighted gene co-expression network method identified 15 hub genes,among which a gene DTZ79＿10g08240 was located at the BSA-seq mapped peak on chromosome 10.The ortholog gene of DTZ79＿10g08240 in A.chinensis was Actinidia29527.Fluorescence quantitative PCR analysis showed that Actinidia29527basically was not expressed in"Hongyang"fruits,while DTZ79＿10g08240 was expressed at a high level in“White”fruits.In addition,the expression level variation trend of DTZ79＿10g08240 during the fruit development process was consistent with AsA content level variation trend.The above results are of great significance for the final reveal of the biological significance and molecular mechanism of AsA hyperaccumulation in A.eriantha.