A NEW METHOD FOR THE IDENTIFICATION AND ISOLATION OF GENES ESSENTIAL FOR ARABIDOPSIS-THALIANA SEED-GERMINATION

Seed viability, dormancy and germination efficiency are very important aspects of the life cycle of plants and their potential to survive an d spread in the environment. To characterize the genes controlling the se processes, we have devised a technique for the selection of mutants impaired in seed germination. Selection for such a trait is complicat ed by physiological factors that interact with these processes and aff ect seed germination efficiency. The distinction between low seed germ ination potential due to physiological factors that interfere with see d maturation or germination and germination deficiency due to genetic factors was based on screening for tagged mutations. Arabidopsis thali ana T-DNA primary transformants obtained by an in planta transformatio n technique are all heterozygotes. We screened for lack of,germination of 1/4 of the seeds in the progeny of independent transformants; and simultaneously for the abnormal segregation (2:1 instead of 3:1) of a kanamycin resistance marker carried by the T-DNA inserted into the gen ome of these primary transformants in the plants that germinate. This yielded several mutants affected in the germination processes. One of the mutants, designated ABC33, was further characterized. Once the via ble embryos from non-germinating seeds were removed from their testa, they grew and displayed a dwarf phenotype which could be complemented by providing gibberellic acid. A genetic and molecular analysis, based on the characterization of the flanking genomic sequences of the T-DN A insert, showed that ABC33 is a new loss-of-function allele at the GA (1) locus.