Expression of globulin-2, a member of the cupin superfamily of proteins with similarity to known food allergens, is increased under high temperature regimens during wheat grain development

Twenty-three expressed sequence tags (ESTs) from the US spring wheat Butte 86 were identified that encode proteins similar to a globulin-2 protein from maize embryos. The ESTs assembled into three contigs, two of which include the entire coding region for the mature protein. The encoded proteins contain two cupin domains and show significant identities with 7S seed proteins from other species that are known or putative food allergens. Quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) with primers specific for two of the sequences demonstrated that the globulin-2 genes are expressed late in grain development and that transcript levels increase when grain is produced under high temperature conditions. Transcripts were detected in both whole grain and endosperm, but levels were significantly higher in whole grain and highest in embryo. In wheat flour, at least 17 protein spots that differ in both size and pI were identified as globulin-2 by 2-DE/MS. Seven of the spots increased more than 2-fold in relative proportion when grain was produced under high temperature regimens. The data suggest that both transcriptional and post-translational mechanisms are involved in the response of globulin-2 to high temperatures.