Al varieties of the tropical japonica rice developed high adaptability to drought stress, hot and dry climatic conditions of regions in Latin America and Africa. Therefore, these varieties may show high levels of water usage efficiency and constitute an excellent material for studying drought tolerance mechanisms in rice. In Brazil, for example, EMBRAPA maintains a germplasm bank enriched with traditional upland rice landraces collected in areas where cultivated rice has been grown since its introduction in the country, centuries ago, and may represent an extraordinary source of genes that control traits of economic importance such as drought tolerance . The determination of the mechanisms directly involved in drought tolerance remains a challenging task since drought is a complex trait that involves several metabolic pathways . The identification and isolation of genes associated with drought tolerance is of major importance in order to better understand this trait and increase the efficiency in developing drought tolerant varieties [8-10]. At the molecular level, the response of roots to water limiting conditions seems to be crucial to trigger drought tolerance mechanisms, since roots are one of the primarysites for stress signal perception in which a signaling mechanism initiates a cascade of gene expression responses to drought. These transcriptional changes can result in successful adaptations leading to stress tolerance by regulating gene expression and signal transduction in the stress response (regulatory proteins) or directly protecting the plant against environmental stress (functional proteins) . Several functional genomic studies of rice have been performed using different approaches such as macro and microarray [12,13], RT-qPCR, SAGE (Serial Analysis of Gene Expression), MPSS (Massive Parallel Signature Sequencing) and more recently oligoarray using the transcriptome of rice to evaluate responses to abiotic stresses . Proteome analyses have also been increasingly employed to complement genomic studies [15-18], however in a lower rate. Although numerous genes and proteins, which potentially contribute to drought tolerance in rice, have been reported [19-22], most of these studies have focused on lowland rice genotypes. Currently, very little is known about gene and protein expression in upland rice [22-25]. Moreover, most ESTs from drought stressed plants available were obtained from libraries constructed using seedlings . There are very few reports on gene expression of drought-stressed plants in the reproductive stage and using root tissue of plants growing PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/16989806 under defined field capacity. The comprehension of drought responses in upland rice is important Dasatinib for designing breeding strategies to develop varieties more tolerant to water constraints. Recently, the tolerance of ten traditional upland varieties of rice submitted to drought stress has been evaluated as part of an effort to identify new sources of drought tolerance in rice . Concomitantly, the root system of two of the above mentioned upland rice genotypes, characterized as susceptible and tolerant to drought stress, have been analyzed at the reproductive stage using genomic and proteomic approaches. Several genes and proteins were identified, which may play important roles in drought tolerance.Methods1. Plant material and phenotypic evaluation Plants of traditional upland rice (O. sativa L. var. japonica) varieties were grown on PVC pipe columns.