Identification of plant stress-responsive determinants in Arabidopsis by large-scale forward genetic screens

All plants sense and adapt to adverse environmental conditions, however, crop plants exhibit less genetic diversity for abiotic stress tolerance than do wild relatives indicating that a genetic basis exists for stress adaptability. Model plant genetic systems and the plethora of molecular genetic resources that are currently available are greatly enhancing our ability to identify abiotic stress-responsive genetic determin-ants. Forward genetic screens of T-DNA mutagenized Arabidopsis thaliana populations in the genetic back-ground of ecotypes C24RD29a-LUC and Col-0 gl1 sos3-1 were carried out to begin an exhaustive search for such determinants. The C24RD29a-LUC screens identified mutants with altered salt/osmotic stress sensitivity or mutants with altered expression of the salt/osmotic/ cold/ABA-responsive RD29a gene. Also, mutations that alter the NaCl sensitivity of sos3-1 were screened for potential genetic suppressors or enhancers of salt-stress responses mediated by SOS3. In total, more than 250 000 independent insertion lines were screened and greater than 200 individual mutants that exhibited altered stress/ABA responses were re-covered. Although several of these mutants have been reported, most have not yet been studied in detail. Notable examples include novel alleles of SOS1 and mutations to genes encoding the STT3a subunit of the oligosaccharyltransferase, syntaxin, RNA polymer-ase II CTD phosphatases, transcription factors, ABA biosynthetic enzyme, Na1 transporter HKT1, and SUMO E3 ligase. The stress-specific phenotypes of mutations to genes that are involved in many basic cellular functions provide indication of the wide range of control mechanisms in cellular homeostasis that are involved in stress adaptation. Key words: CCD imaging, osmotic stress, RNA polymerase II, salinity, T-DNA tagging, transcription