Deciphering the genetic and molecular control of the develot of the root system and its adaptive response to the availability of nutrients and water is of primary importance for the sustainable establishment of the rice crop under adverse environments. Rice displays a complex root structure-comprising several root types and a large variation in root architecture that reflects adaptation to cropping systems. Our group is exploring various approaches to investigate the control of constitutive development of roots and its adaptation in response to abiotic stresses. Root typology, meristem organization and tissue specification have been investigated first in comparison to Arabidopsis. Specific anatomical features include radial patterning, variation in number of radial cells, number of cells constituting the quiescent centre and tissues participating in lateral root formation. Recent progresses in bi photon imaging now permit a non destructive in situ observation throughout the root tissue. This allows to precisely analyze cell lineages using GFP-marked Enhancer Trap lines and will permit to study protein trafficking and interactions in specific cell types. Cloning and characterization of architectural genes identified both through QTL analysis and screening of insertion mutants altered in root development is underway. A genome-wide comparison of A. thaliana root development genes through reverse genetics in rice is undertaken. We first developed a comparative database for genome-wide comparison of A. thaliana and O. sativa genic repertoire. GreenPhylDB (http://www.greenphyldb.cirad.fr) nowadays comprises the most complete list of plant gene families (6,421 families) which have been manually curated. GreenPhylDB also contains all the phylogenomic relations computed for 4,375 families. We extracted rice orthologs for a total of 60 genes involved in root development in A. thaliana. Based on the reference rice root typology and root meristem fate we identified surprisingly