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.