Rice (Oryza sativa) is the second major crop around the world. In Brazil, the state of Rio Grande do Sul detains 45% of the national production. Over 80% of production is done in the irrigated system, where the plants are covered by a water layer. In this anaerobic environment, the pH decreases and iron becomes more available to absorption, leading to iron excess. This could lead to leaf chlorosis, reduction of plant growth and fertility, and even to death. The cDNA- Representational Difference Analysis (cDNA-RDA) is based on the subtractive hybridization of a "tester" population with a "driver" population, followed by PCR, in order to isolate sequences specific of the tester. We have extracted total RNA from rice shoots submitted to iron excess (500 ppm) or to control treatment (6.5 ppm) for 3, 6 and 9 days. The cDNA synthesis was done using a pool of 300 ng of RNA from each time of treatment, for both situations. The cDNAs were cleaved with MboI, ligated to RBam adaptors and amplified to generate the two driver populations. An aliquot of both was cleaved with MboI and ligated to JBam adapters to generate the tester populations. Then, hybridization was done using tester from one situation with driver from another situation in a 1:50 proportion. After amplification with JBam primer, Differential Product 1 (DP1) for iron excess and for control situations were obtained. Both DP1 were cleaved with MboI and ligated to NBam adapters. The second hybridization was done using DP1 and driver in a 1:500 proportion. After amplification, Differential Product 2 (DP2) for both situations were obtained. DP2 sequences were cloned into pCR 2.1-TOPO Vector.  The iron excess library (which is expected to be enriched for sequences up-regulated in iron excess) and the control library (which is expected to be enriched for sequences down-regulated in iron excess) were obtained. Both libraries were transformed in Escherichia coli XL1-Blue lineage, 384 colonies per library were isolated and stocked at -80ºC. In a first sequencing effort, 192 clones from each library are being sequenced. Northern blot analysis at the three treatment times (3, 6 and 9 days) will be used to confirm the differential expression pattern of the sequences.