The slender rice mutant, with constitutively activated gibberellin signal transduction, has enhanced capacity for...

The slender rice (slr1-1) mutant, carrying a lethal and recessive single mutation, has a constitutive gibberellin (GA)-response phenotype and behaves as if it were saturated with GAs [Ikeda et al. (2001) Plant Cell 13, 999]. The SLR1 gene, with sequence homology to members of the plant-specific GRAS gene family, is a mediator of the GA signal transduction process. In the slender rice, GA-inducible alpha-amylase was produced from the aleurone layer without applying GA. GA-independent alpha-amylase production in the mutant was inhibited by applying abscisic acid (ABA). Shoot elongation in the mutant was also suppressed by ABA, indicating that the slender rice responds normally to ABA. Interestingly, shoot ABA content was 10-fold higher in the mutant than in the wild type, while there was no difference in root ABA content. Expression of the Rab16A gene, which is known to be ABA inducible, was about 10-fold higher in shoots of the mutant than in those of the wild type. These results indicate that constitutive activation of the GA signal transduction pathway by the slr1-1 mutation promotes the endogenous ABA level.