Transcriptomic and Metabolomic Analysis of Wheat Kernels in Response to the Feeding of Orange Wheat Blossom Midges (Sitodiplosis mosellana) in the Field

The orange wheat blossom midge (Sitodiplosis mosellana Géhin) is an insect
pest that feeds on wheat (Triticum aestivum L.). The resistance mechanisms
of wheat to S. mosellana infestation
are largely unknown. In this study, the wheat varieties LX99 and 6218
were identified as highly resistant and susceptible, respectively,
via field investigations conducted over two consecutive years. Morphological
and microstructural observations of mature wheat kernels following S. mosellana infestation revealed that the degree
of cell structure damage in resistant LX99 grains was less than that
in susceptible 6218 grains. Transcriptomic and metabolomic analyses
of seeds following S. mosellana feeding
showed that the differentially expressed genes and differentially
accumulated metabolites from LX99 were mostly enriched in several
primary and secondary metabolic pathways, including phenylpropanoid
biosynthesis, flavonoid biosynthesis, and phenylalanine biosynthesis.
Additionally, phenylpropanoid- and flavonoid-related gene expression
was significantly upregulated following S. mosellana infestation in LX99 relative to that in 6218. Some metabolites involved
in phenylpropanoid/flavonoid pathways, such as cinnamic acid, coumarin,
epigallocatechin, and naringenin, were only induced in infested LX99
kernels. These results suggest that phenylpropanoid/flavonoid pathways
play important roles in wheat kernel resistance to S. mosellana attack and provide useful insights for
the breeding and utilization of resistant varieties.