Identification of the Grapefruit (<i>Citrus paradisi</i>) Isocitrate Dehydrogenase Gene and Functional Analysis of <i>CpNADP-IDH1</i> in Citric Acid Metabolism
2025
Longfei Jin | Yang Yue | Feng Liu | Mingxia Wen | Bei Huang | Peng Wang
Citric acid serves as the principal organic acid in citrus fruits, with its concentration critically determining fruit flavor and market acceptability. Isocitrate dehydrogenase (IDH), a key enzyme in citric acid metabolism, mediates the conversion of citrate to α-ketoglutarate. This study cloned six candidate genes encoding IDH from grapefruit (<i>Citrus paradisi</i>). Bioinformatics analysis showed that all six genes contained the typical characteristic structure of IDH. Gene expression analysis found that <i>CpNADP-IDH1</i> is highly expressed in mature and low-acid varieties. Overexpression of <i>CpNADP-IDH1</i> significantly increased IDH enzyme activity and decreased citric acid content in transgenic grapefruit callus. These results showed that at least six genes encoding IDH exist in grapefruit, among which <i>CpNADP-IDH1</i> catalyzes the decomposition of citric acid and regulates the organic acid content in fruits at maturity. <i>CpNADP-IDH1</i> can be used as a candidate gene for molecular breeding of low-acid citrus varieties and as an essential target gene for developing citrus cultivation technology for reducing acid content.
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