Transcriptomic and Gas Chromatography–Mass Spectrometry Metabolomic Profiling Analysis of the Epidermis Provides Insights into Cuticular Wax Regulation in Developing ‘Yuluxiang’ Pear Fruit

The
layer of cuticular wax covering fruits plays important roles
in protecting against disease, preventing non-stomatal water loss,
and extending shelf life. However, the molecular basis of cuticular
wax biosynthesis in pear (Pyrus) fruits
remains elusive. Our study thoroughly investigates cuticular wax biosynthesis
during pear fruit development from morphologic, transcriptomic, and
gas chromatography–mass spectrometry metabolomic perspectives.
Our results showed that cuticular wax concentrations increased during
the early stage [20–80 days after full bloom (DAFB)] from 0.64
mg/cm2 (50 DAFB) to 1.75 mg/cm2 (80 DAFB) and
then slightly decreased to 1.22 mg/cm2 during the fruit
ripening period (80–140 DAFB). Scanning electron microscopy
imaging indicated that wax plate crystals increased and wax structures
varied during the pear fruit development. The combined transcriptomic
and metabolomic profiling analysis revealed 27 genes, including 12
genes encoding transcription factors and a new structural gene (Pbr028523) encoding β-amyrin synthase, participating
in the biosynthesis, transport, and regulation of cuticular wax according
to their expression patterns in pear fruit. The quantitative real-time
polymerase chain reaction experiments of 18 differentially expressed
genes were performed and confirmed the accuracy of the RNA-Seq-derived
transcript expression. A model of VLCFAs and cuticular wax synthesis
and transport in pear fruit is proposed, providing a mechanistic framework
for understanding cuticular wax biosynthesis in pear fruit. These
results and data sets provide a foundation for the molecular events
related to cuticular wax in ‘Yuluxiang’ pear fruit and
may also help guide the functional analyses of candidate genes important
for improving the cuticular wax of pear fruit in the future.