Post-Anthesis Fertilizer Influences Expression of Genes Encoding Allergenic Proteins

摘要

Omega-gliadins comprise between 5-10% of the wheat flour protein and have been implicated in food allergies. In particular, omega-gliadins encoded by the IB chromosome have been associated with wheat-dependent exercise-induced anaphalaxis (WDEIA) andurticaria in adults and immediate-type wheat allergies in children. Because the omega-gliadins consist almost entirely of repetitive sequences, the genes encoding these proteins have proved difficult to clone. Therefore, the complement of omega-gliadin genes expressed in the US spring wheat 'Butte 86' was surveyed by examining expressed sequence tags (ESTs) available from the TIGR Wheat Gene Index (http://www.tigr.org/). Fifteen ESTs from 'Butte 86' fell into 5 gene assemblies. Three of the assemblies encode proteins with PQQPFP as the predominant repetitive motif and are similar to proteins encoded on chromosomes 1A and ID. In one of these, the substitution of a T with a G in the DNA sequence results in the replacement of a phenylalanine residue witha cysteine and suggests that the protein may be incorporated into the glutenin polymer. The other two gene assemblies encode proteins with FPQQQ and QQIPQQ repeats and are similar to omega gliadins encoded on chromosome IB. Primers specific for the two types of omega-gliadin genes were designed and quantitative real time RT-PCR was used to investigate the accumulation of transcripts in developing wheat grains produced with or without post-anthesis fertilizer supplied as NPK 20-20-20. Transcripts for both types of omega-gliadin proteins were detected at 8 days post-anthesis (DPA). The levels of transcript changed little between 8 and 32 DPA in the absence of NPK. When plants were supplied with NPK, transcript levels increased gradually between 8 and 32DPA so that levels of omega-gliadin transcripts were significantly higher in grains that received NPK than in those that did not. Transcripts for a gamma-gliadin showed a different profile, with the greatest amounts of transcripts during mid-stages of grain development. In contrast to omega-gliadins, both the timing and levels of gamma-gliadin transcripts changed little in response to NPK. The data suggest that the application of nitrogen to improve grain protein content may also lead to increased levels of one type of allergenic protein.