Proteomic analysis reveals developmentally expressed rice homologues of grass group II pollen allergens

Three isoallergens of Ory s 2, homologues of grass group II pollen allergens, were identified from rice and characterised by proteome and immunochemical analyses. The N-terminal amino acid sequence profiles of three proteins on a 2-dimensional electrophoresis (2-DE) gel of rice pollen proteins matched 100% to the protein sequences encoded by three rice expressed sequence tags (ESTs). The deduced protein sequences from these ESTs share sequence identities of 41-43% with the protein sequences of the group II pollen allergens of different grasses, and sequence identity of 39% with the C-terminal portion of rice group I pollen allergens. Signal peptide sequences, which are similar to the leader peptides of other major pollen allergens, are also present in the deduced amino acid sequences. Polyclonal antibodies, produced in rabbits using Ory s 2 proteins purified by 2-DE, were used to investigate the developmental-stage- and tissue-specific expression of Ory s 2 by immunochemical analysis. Results of immunochemical experiments show that Ory s 2 proteins are expressed only at the late stage of pollen development and they do not have cross-reactivity with group II pollen allergens from some other common grasses.