THE ELONGATED GENE OF ARABIDOPSIS ACTS INDEPENDENTLY OF LIGHT AND GIBBERELLINS IN THE CONTROL OF ELONGATION GROWTH

A novel elongated mutant has been isolated from EMS-mutagenized popula tions of the Arabidopsis thaliana ga4 mutant. After backcrossing with the Landsberg erecta (Ler) wild-type (WT) followed by selfing, the mut ant phenotype was identified in the GA4 background. Seedlings of the m utant, which has been named elg(elongated), are characterized by elong ated hypocotyls and petioles, leaves that are narrow and somewhat epin astic and early flowering. Allelism tests with the hy1-hy5 mutants ind icate that elg is not allelic with any of these long-hypocotyl mutants . From linkage analyses, the location of elg on chromosome 4, between cer2 and ap2 has been established. The pleiotropic phenotype of elg se edlings is suggestive of a disruption of phytochrome and/or gibberelli n (GA) function. Although the elg mutant displays a light-dependent lo ng-hypocotyl phenotype, elg seedlings retain a full range of photomorp hogenic responses and the elg mutation acts additively with the photom orphogenic mutants phyB, hy1 and hy2. This suggests that ELG acts inde pendently of phytochrome action. The elg mutation partially suppresses the effect of GA-deficiency on elongation growth, and, although elg g al seedlings are more elongated than gal seedlings, both genotypes res pond in the same way to applied GA, That applied GA and the elg mutati on interact additively suggests that ELG acts independently of GA acti on.