Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 8, 2008
Publication Date: January 1, 2009
Citation: Altenbach, S.B., Tanaka, C.K., Hurkman II, W.J., Vensel, W.H. 2009. Expression of globulin-2, a member of the cupin superfamily of proteins with similarity to known food allergens, is increased under high temperature regimen during wheat grain development. Journal of Cereal Science. 49:47-54. Interpretive Summary: In wheat, the major grain storage proteins that serve as a source of amino acids for the developing seedling are the gliadins and glutenin subunits, generally referred to as the gluten proteins. However, wheat grains also contain lesser amounts of salt-soluble proteins, or globulins, that are similar to the major 7S storage proteins found in seeds from dicotyledonous plants. It was suggested previously that these proteins have no biological role in cereals other than storage. DNA sequences encoding three globulins expressed in the US bread wheat Butte 86 were identified in public databases. Based on these sequences, quantitative methods were developed to evaluate the expression of two of the genes. The data demonstrate that the wheat globulin genes are expressed late in grain development and that the levels of expression are enhanced when grain is produced under high temperature conditions. The results suggest a biological role for the proteins in the response of the wheat grain to high temperatures. These results are of significance because the wheat globulins show similarities to proteins that are known food allergens in other plant species.
Technical Abstract: 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 two-fold in relative proportion when grain was produced under high temperature regimens. The data suggest a biological role for globulin-2 in the response of the wheat grain to high temperature stress and indicate that the response involves both transcriptional and post-translational mechanisms.