Common bean ( Phaseolus vulgaris L.) is the most important grain legume for direct human consumption, it comprises fifty percent of the grain legume consumed worldwide. In several countries (Mexico, Brazil) common bean is nutritionally very important as one of the primary sources of dietary protein. In addition to their impacts on human health, legumes are vital in agricultural systems as they form symbiotic associations with nitrogen-fixing bacteria. The original microsymbiont of P. vulgaris is Rhizobium etli but symbioses can also be established with other rhizobial species such as: R. tropici , R. leguminosarum bv phaseoli, and Rh. sp. NGR234. The interaction between legume plants and rhizobia leads to the formation of the nodule, a organ virtually unique to legumes.
Phaseolus sp. are one of the most ancient crops in the Americas. A nucleus of diversity of P. vulgaris is located in Ecuador and Northern Peru, from where beans dispersed to form two distinct gene pools, the Andean and Mesoamerican gene pools.
The features mentioned above, among others, make common bean a useful legume species for genomic studies. An international consortium called Phaseomics ( PHASEOlus genoMICS ), that includes 100 scientists from 20 different countries interested in genomic research on beans, has been formed ( www.phaseolus.net ). Phaseomics was developed with the intent to establish the necessary framework of knowledge and materials for the advancement of bean genomics, transcriptomics and proteomics.
Partial sequencing of cDNA inserts or expressed sequence tags (ESTs), obtained from many tissues and organs, has been used as an effective method of gene discovery, molecular marker generation, and transcript pattern characterization. It is an efficient approach for identifying large number of plant genes expressed during different developmental stages, and in response to a variety of environmental conditions. Despite the importance of common beans as a crop legume, very little EST information is currently available. For this reason we have undertaken a survey of the bean transcriptome by analyzing ESTs from diverse tissues as part of a collaborative project within the framework of Phaseomics .