| Ziziphus jujuba Mill.is the most important economic tree species in Rhamnaceae.It is domesticated and bred from Ziziphus jujuba var.spinosa,with large fruit,sweet taste,high content of VC and rich nutrition.As a natural component of fruit,organic acids play an important role in determining fruit flavor and nutrition.In this study,three different types of jujube,sour jujube and transitional type were selected as the representative of the germplasm.The accumulation trend of organic acid content during fruit development was analyzed by High Performance Liquid Chromatography（HPLC）.Furthermore,the organic acid accumulation characteristics of sour jujube（41 diverse individuals）and cultivated jujube（21diverse varieties）populations were detected.According to the results of organic acid determination,the transcriptome of 5 samples with high acid content and 5 varieties with low acid content at mature stage were sequenced and analyzed to screen and identify the key genes regulating the formation of organic acids in fruits and reveal the molecular mechanism of the formation of organic acid quality in jujube fruits.The results are of great significance for the evaluation of jujube germplasm resources and domestication and breeding research.The main results are as follows:1.The results of determination of organic acid content in different stages of fruit development showed that the citric acid content of jujube decreased significantly with fruit ripening,and the citric acid content was very low in the whole red stage.The content of citric acid in sour jujube was accumulated with fruit ripening,.In the whole developmental stage,the content of malic acid was as follows:sour jujube>Transitional type>Jujube.2.The analysis of organic acids of jujube and sour jujube population showed that the organic acids of sour jujube were mainly citric acid(the average content of citric acid in each sample was 9.96 mg·g-1),and contained high malic acid(the average content was 8.07 mg·g-1).The contents of citric acid and malic acid in the transitional type were low(the average contents were 7.37 mg·g-1 and 6.75 mg·g-1,respectively).The average organic acid content of jujube fruit was only 1/3 of that of jujube fruit.The organic acids of jujube were mainly malic acid(average content was 1.62 mg·g-1),and very low citric acid(average content was 1.33mg·g-1).Ascorbic acid（ASA）/VC was abundant in the sour jujube population with high organic acid content.The ASA content in jujube with middle or low acid varies greatly.Correlation analysis showed that the citric acid content was significantly positively correlated with malic acid in both sour jujube and jujube;the quinic acid content was negatively correlated with citric acid in both jujube and jujube;the ASA content was significantly positively correlated with citric acid content in sour jujube and jujube,and significantly positively correlated with malic acid in jujube.The analysis of organic acids in different samples is of great significance for germplasm resources evaluation and breeding.3.Transcriptome sequencing was performed on 5 sour jujbe fruit and 5 jujube fruit..A total of 5693 differentially expressed genes,with 1563 genes up-regulated and 4130 down-regulated,These genes are enriched in ribose metabolism（KO03010）,amino acid biosynthesis（KO01230）,phenylalanine,tyrosine and tryptophan biosynthesis（KO00400）,flavonoid biosynthesis（KO00941）,and ascorbic acid and aldehyde acid metabolism（KO00053）,respectively.A total of 21 differential genes related to organic acid metabolism and transport were screened.4.We analyzed the correlation of organic acid content and organic acid accumulation rel ated genes in the above transcriptome samples.It was found that the citric acid degradation ge ne ZjAco3 was negatively correlated with the citric acid content,and the aluminum-activated malate transporter ZjAl MT4 was positively correlated with the malic acid content.Further qua ntitative analysis of ZjAco3 and ZjALMT4 in 21 jujube cultivars and 41 sour jujube samples w as carried out,and the correlation between gene expression and organic acid content was calc ulated at the population level.The results were consistent with the above.In addition,the activ ity of ACO enzyme was also significantly enhanced during the ripening process of jujube fruit s.We speculated that ZjAco3 was the key gene for citric acid degradation in jujube fruits.ZjA LMT4 plays an important role in the transport and accumulation of malic acid... |
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