Watercore is a physiological disorder which often occurs on the pear fruit and the excessive accumulation of
sorbitol in fruit intercellular space is considered to be an important cause of watercore. Our previous studies found that the metabolic disorder of
sugars may lead to
hypoxia stress and disturb respiration, resulting in aggravated fruit rot and the formation of bitter substances. However, the further changes of respiration and the fruit response mechanism are not well understood. A comprehensive transcriptome analysis of 'Akibae' pear watercore fruit was performed in this study. The transcriptome results revealed the
hypoxia stress significantly induced the expression of several key
enzymes in the TCA cycle and may lead to the accumulation of
succinic acid in watercore fruit. The glycolytic pathway was also significantly enhanced in watercore fruit. Moreover, the γ-
aminobutyric acid (
GABA) synthesis related genes,
glutamate decarboxylase (GAD) genes and
polyamine oxidase (PAO) genes, which associated with the
GABA shunt and the
polyamine degradation pathway were significantly upregulated. In addition, the PpGAD1 transcript level increased significantly along with the increase of GAD activity and
GABA content in the watercore fruit. Above all, these findings suggested that the hypoxic response was marked by a significant increase of the
hypoxia-inducible metabolites
succinic acid and
GABA and that PpGAD1 may play a key role in response to watercore by controlling the
GABA synthesis.