A survey of six organ-/tissue-specific proteomes of the model legume barrel medic (Medicago truncatula) was performed. Two-dimensional polyacrylamide gel electrophoresis reference maps of protein extracts from leaves, stems, roots, flowers, seed pods, and cell suspension cultures were obtained. Five hundred fifty-one proteins were excised and 304 proteins identified using peptide mass fingerprinting and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Nanoscale high-performance liquid chromatography coupled with tandem quadrupole time-of-flight mass spectrometry was used to validate marginal matrix-assisted laser desorption ionization time-of-flight mass spectrometry protein identifications. This dataset represents one of the most comprehensive plant proteome projects to date and provides a basis for future proteome comparison of genetic mutants, biotically and abiotically challenged plants, and/or environmentally challenged plants. Technical details concerning peptide mass fingerprinting, database queries, and protein identification success rates in the absence of a sequenced genome are reported and discussed. A summary of the identified proteins and their putative functions are presented. The tissue-specific expression of proteins and the levels of identified proteins are compared with their related transcript abundance as quantified through EST counting. It is estimated that approximately 50% of the proteins appear to be correlated with their corresponding mRNA levels.

Biotic interactions in the rhizosphere are biologically important, and although many of those interactions have been well studied, the role of secreted proteins in the cross-talk between microbes and roots has not been investigated. Here, protein secretion was studied during the communication between the roots of two plants (Medicago sativa and Arabidopsis thaliana) and the bacterial symbiont of one of these species (Sinorhizobium meliloti strain Rm1021) and an opportunistic bacterial pathogen of A. thaliana (Pseudomonas syringae pv. tomato DC3000) using a proteomic approach. It was found that protein exudation in the M. sativa-S. meliloti interaction caused an increase in the secretion of seven plant proteins, such as hydrolases, peptidases, and peroxidases among others in two or more time points compared with the plant control. In addition, four proteins, all of bacterial origin, were increased 1.5-fold more in this interaction compared with S. meliloti alone. However, these proteins were not induced when M. sativa was inoculated with P. syringae DC3000. The interaction between A. thaliana and P. syringae DC3000 highly induced the secretion of several plant proteins related to defense soon after initial contact with P. syringae, but these proteins were not secreted in the incompatible interaction with S. meliloti. The results of this study reveal a specific, protein level cross-talk between roots and microbes. These results suggest that secreted proteins may be a critical component in the process of signaling and recognition that occurs between compatible and incompatible interactions.

No abstract

BackgroundWhite lupin (Lupinus albus L.) roots efficiently take up and accumulate (heavy) metals, adapt to phosphate deficiency by forming cluster roots, and secrete antimicrobial prenylated isoflavones during development. Genomic and proteomic approaches were applied to identify candidate genes and proteins involved in antimicrobial defense and (heavy) metal uptake and translocation.ResultsA cDNA library was constructed from roots of white lupin seedlings. Eight thousand clones were randomly sequenced and assembled into 2,455 unigenes, which were annotated based on homologous matches in the NCBInr protein database. A reference map of developing white lupin root proteins was established through 2-D gel electrophoresis and peptide mass fingerprinting. High quality peptide mass spectra were obtained for 170 proteins. Microsomal membrane proteins were separated by 1-D gel electrophoresis and identified by LC-MS/MS. A total of 74 proteins were putatively identified by the peptide mass fingerprinting and the LC-MS/MS methods. Genomic and proteomic analyses identified candidate genes and proteins encoding metal binding and/or transport proteins, transcription factors, ABC transporters and phenylpropanoid biosynthetic enzymes.ConclusionThe combined EST and protein datasets will facilitate the understanding of white lupin's response to biotic and abiotic stresses and its utility for phytoremediation. The root ESTs provided 82 perfect simple sequence repeat (SSR) markers with potential utility in breeding white lupin for enhanced agronomic traits.

The proteome of a Medicago truncatula cell suspension culture was analyzed using two-dimensional electrophoresis and nanoscale HPLC coupled to a tandem Q-TOF mass spectrometer (QSTAR Pulsar i) to yield an extensive protein reference map. Coomassie Brilliant Blue R-250 was used to visualize more than 1661 proteins, which were excised, subjected to in-gel trypsin digestion, and analyzed using nanoscale HPLC/MS/MS. The resulting spectral data were queried against a custom legume protein database using the MASCOT search engine. A total of 1367 of the 1661 proteins were identified with high rigor, yielding an identification success rate of 83% and 907 unique protein accession numbers. Functional annotation of the M. truncatula suspension cell proteins revealed a complete tricarboxylic acid cycle, a nearly complete glycolytic pathway, a significant portion of the ubiquitin pathway with the associated proteolytic and regulatory complexes, and many enzymes involved in secondary metabolism such as flavonoid/isoflavonoid, chalcone, and lignin biosynthesis. Proteins were also identified from most other functional classes including primary metabolism, energy production, disease/defense, protein destination/storage, protein synthesis, transcription, cell growth/division, and signal transduction. This work represents the most extensive proteomic description of M. truncatula suspension cells to date and provides a reference map for future comparative proteomic and functional genomic studies of the response of these cells to biotic and abiotic stress. Legumes (Fabaceae) are one of the most economically important crop families in the world and are characterized by their unique ability to fix atmospheric nitrogen through a symbiotic relationship with soil bacteria. These bacteria, collectively termed Rhizobia and which include genera such as Rhizobium, Sinorhizobium, Bradyrhizobium, Mesorhizobium, and Azorhizobium, form specialized organs within the plant, and nitrogen fixation occurs via the conversion of N 2 into NH 3 by bacterial nitrogenases. The mutualistic interactions provide a plentiful supply of nitrogen to the plants that in turn results in very high protein levels in legumes. Therefore, legumes have been assimilated as a major dietary source of protein for both humans and animals. Legumes also provide nitrogen to the soil, thus reducing the need for exogenous fertilizers. Legumes are also a unique source of natural products such as isoflavonoids, alkaloids, and saponins, many of which have documented antimicrobial and pharmacological properties (1-3). Based on the above traits, legumes have significant economic and ecological value. For example, soybeans provide more than one-third of human protein intake and approximately half of the world's supply of oilseed. Over 73 million acres of soybeans (Glycine max) and 76 million acres of alfalfa (Medicago sativa) were cultivated in the United States in 2003 and have estimated values of $17.5 billion and $7.5 billion, respectively (4).The mutualistic interactions between legu...