Genetic analysis of salt-tolerant mutants in Arabidopsis thaliana

Stress caused by the increased salinity of irrigated fields impairs plant g rowth and is one of the major constraints that limits crop productivity in many important agricultural areas. As a contribution to solving such agrono mic problems, we have carried out a large-scale screening for Arabidopsis t haliana mutants induced on differ ent genetic backgrounds by EMS treatment, fast neutron bombardment, or T-DNA insertions. From the 675,500 seeds we s creened, 17 mutant lines were isolated, all but one of which yielded 25-70% germination levels on 250 mM NaCl medium, a condition in which their ances tor ecotypes are unable to germinate. Monogenic recessive inheritance of Na Cl-tolerant germination was displayed with incomplete penetrance by all the selected mutants, which fell into five complementation groups. These were named SALOBRENO (SAN) and mapped relative to polymorphic microsatellites, t he map positions of three of them suggesting that riley are novel genes. St rains carrying mutations in the SAN1-SAN4 genes display similar responses t o both ionic effects and osmotic pressure, their germination being NaCl and mannitol tolerant but KCL and Na2SO4 sensitive. In addition, NaCl-, KCl-, and mannitol-tolerant as well as abscisic-acid-insensitive germination was displayed by san5, whose genetic and molecular characterization indicates t hat it carries an extremely hypomorphic or null allele of the AB14 gene, it s deduced protein product lacking the APETALA2 DNA binding domain.