Isolation of genes responsive to water stress in potato cell cultures

Drought is one of major stress limiting factors for crop productivity. This stress condition affects almost all plant functions, including growth and development. Plants respond to osmotic stresses by activating mechanisms of repair and protection of cellular metabolism as a result of the action of different genes that operate in a complex and coordinate network. In order to identify key genes involved in response to drought, we studied the differential expression of potato cells upon PEG-mediated osmotic stress of different intensity (5-20% PEG) and duration (15min, 1h, 24h). The systematic comparison, by cDNA-AFLP, of changes in gene expression during gradual adaptation to low water potential with those induced by abrupt exposure to water stress, allowed to identify cDNA fragments specific for each response. As first screening, about 60 cDNAs fragments were identified as to be differentially expressed. Fourteen cDNA clones were isolated and their pattern of expression confirmed a clear up-regulation upon stress as determined by RT-PCR. Many of these AFLP tags match typical stress responsive genes belonging to different functional classes, i.e. protein synthesis (elongation factor 1a, ribosomal proteins), chaperone activity and protein degradation (hsp20, RER), ROS scavenging pathway (phenylalanine ammonia-lyase, peroxidase). Sequence homology search revealed that the remaining six cDNA clones encode hypothetical or unknown proteins, never described as to be stress- inducible before. Three cDNAs are highly homologous to potato or tomato EST, one homologous to a cDNA expressed during arabidopsis seed development. When potato cDNA sequences were converted into arabidopsis hortologs, conserved domains were identified, such as plant DNA binding homodomain (clone #96) or transmembrane domains (clones #102 and 103). No hits were found in current databases for fragments #114 and 131. Further characterization of the most interesting clones is in progress for the isolation of the corresponding full-length cDNAs and the functional analysis of the genes in arabidopsis mutants.