Objective  The biological function of AheCS gene and the correlation between citric acid content and relative expression of AheCS gene were analyzed, and the possible role of AheCS gene in the metabolism of organic acids in jackfruit was discussed.

  Method   AheCS1, AheCS2, and AheCS3 from fruits of A. heterophyllus Haida 2 were cloned for a bioinformatic analysis. At room temperature(22±1℃) and 90% RH, changes on the gene expression and citric acid content in the fruits under natural ripening process or exposed to either 0.5 mg·L⁻¹ of 1-MCP or 1,000 mg·L⁻¹ of 40% ethylene (ETH) were determined.

  Result  The citric acid content in a naturally ripening jackfruit gradually rose and declined subsequently. It increased at an accelerated rate when exposed to ETH, but the rate was slowed down by the 1-MCP treatment. The ORFs of the three genes ranged from 1 422 bp to 1 827 bp containing conserved WPNVDAHS domain and belonging to the CS family. The amino acid sequences were phylogenetically closely related to those of CsCS (MH_048698.1) in citrus with a similarity of 86.49%, MnCS (XP010087965.1) in mulberry with a similarity of 97%, and AaCS (JAT55223.1) in anthurium with a similarity of 86%. The expressions of these genes were low in the early stage and raised subsequently during natural ripening (CK). However, the exogenous ETH hastened the increasing rate of AheCS1 expression and elevated the levels of AheCS2 and AheCS3 expressions, while 1-MCP delayed the rise but heightened the expression levels of the three genes at the stage near fruit maturity. The citric acid content of the ripening fruits generally positively correlated with the gene expressions. The correlation with AheCS2 reached a statistically significant level.

  Conclusion  AheCS2 is a potential gene involved in the regulation of citric acid accumulation during the ripening process of jackfruit, and it can be a candidate gene for further study of the function and genetic improvement of the AheCS gene in jackfruit .