Diversity of rice glutelin polypeptides in wild species assessed by the higher-temperature sodium dodecyl sulfate-polyacrylamide gel electrophoresis and subunit-specific antibodies.

ABSTRACT

In efforts to find genetic resources with high nutritional value of rice seed, we assessed the diversity of the major storage protein glutelin in 13 wild and 2 cultivated rice species by a unique SDS-PAGE method and subunit-specific antibodies. Maximum separation of microheterogeneous glutelin alpha-polypeptides, which is a prerequisite for the diversity evaluation, could be attained by SDS-PAGE performed at higher temperature (45 degrees C) than the generally employed temperatures (4-25 degrees C). Seven antipeptide antibodies were raised against subunit-specific epitope sequences designed at five sites from four variable regions spanning the glutelin alpha-polypeptides. High specificity of each antibody was confirmed using rice glutelin mutants, and demonstrated considerable variation in amino acid sequence and accumulation level of glutelin subunit in wild species, in combination with the higher-temperature SDS-PAGE. The degree of the variation was, however, changed according to the site of variable regions and the type of subunit. Some wild species accumulated nutritious GluB subunits more than cultivated rice. The wild species Oryza longiglumis and O. brachyantha had glutelin with low reactivity against most antibodies examined in this study, reflecting the significant divergence. Such wild species may hopefully serve as important genetic resources for nutritional improvement of cultivated rice.