Gibberellin response mutants identified by luciferase imaging

Summary The gibberellin (GA) 20‐oxidase encoded by Arabidopsis GA5 catalyzes the synthesis of active GAs. GA5 is a regulatory step in GA biosynthesis as GA5 mRNA levels are negatively regulated by its bioactive GA products. A fusion between the GA5 promoter and the firefly luciferase reporter ( GA5 ‐ LUC ) was shown to be similarly regulated, indicating GA feedback of GA5 occurs at the transcriptional level. The fidelity of the GA5 ‐ LUC reporter permitted a fusion genetic screen to identify mutants altered in transgene expression. This bioimaging screen identified two types of recessive mutants with increased LUC activity and apparent GA‐related growth phenotypes, a dwarf ( lue1 ) and two late flowering mutants ( fpa1‐3 and fpa1‐4 ). Mutant progeny exhibited altered levels of LUC and of endogenous GA5 and other GA‐regulated mRNAs. SSLP‐based mapping localized lue1 to chromosome I near the ga2 locus, although complementation analyzes showed that lue1 is not allelic to ga2 . Mapping and complementation analyzes showed that the late flowering mutants are allelic to fpa1 . This provides genetic evidence for crosstalk between the autonomous and gibberellin‐dependent flowering pathways.