Characterization of the Genes Involved in Malic Acid Metabolism from Pear Fruit and Their Expression Profile after Postharvest 1‑MCP/Ethrel Treatment

In this study, five genes involved in malic acid (MA) metabolism, including a cytosolic NAD-dependent malate dehydrogenase gene (cyNAD-MDH), a cytosolic NADP-dependent malic enzyme gene (cyNADP-ME), two vacuolar H+-ATPase genes (vVAtp1 and vVAtp2), and one vacuolar inorganic pyrophosphatase gene (vVPp), were characterized from pear fruit based on bioinformatic and experimental analysis. Their expression profile in “Housui” pear was tissue-specific, and their expression patterns during fruit development were diverse. During “Housui” pear storage, MA content decreased, which was associated with the downregulated transcripts of MA metabolism-related genes and cyNAD-MDH activity and higher cyNADP-ME activity. The response of MA metabolism to postharvest 1.5 μL L–1 1-MCP fumigation and 0.5 mL L–1 ethrel dipping was distinct: 1-MCP fumigation upregulated gene expression and cyNAD-MDH activity and suppressed cyNADP-ME activity, and thus maintained higher MA abundance when compared with those in the control; on the other hand, an opposite behavior was observed in ethrel-treated fruit.