Proteomic analysis of cytoskeleton-associated RNA binding proteins in developing rice seed.

In eukaryotes, RNA binding proteins (RBPs) play an integral role not only in RNA processing within the nucleus, but also in the cytoplasmic events of RNA transport, localization, translation, storage and degradation. While many studies have been done, relatively little is known about RBPs in plants. As part of our continuing efforts to understand cytoplasmic gene expression events in developing rice seed (Oryza sativa L.), a proteomics approach was used to identify cytoplasmic-localized, cytoskeletal-associated RBPs. The nucleic acid binding fraction from a cytoskeletal-enriched rice seed extract was isolated by Poly(U)-Sepharose affinity chromatography and analyzed using 2D gel electrophoresis. Analysis of 162 excised protein spots using mass spectrometry led to the identification of 148 distinct proteins, in addition to the highly abundant globulin and glutelin seed storage proteins. Identified proteins include those involved in RNA processing, translation, protein modification, cell signaling, and metabolism, as well as a number of hypothetical proteins. Proteins of particular interest with roles in RNA metabolism are discussed. These results have been deposited within the Rice RNA Binding Protein Database as part of an integrated study of plant cytoskeletal-associated RBPs using developing rice seed as a model.