EARLY FLOWERING3 regulates flowering in spring barley by mediating gibberellin production and FLOWERING LOCUS T expression

<i>EARLY FLOWERING3 (ELF3)</i> is a circadian clock gene that contributes to photoperiod-dependent flowering in plants, with loss-of-function mutants in barley (<i>Hordeum vulgare</i>), legumes, and Arabidopsis thaliana flowering early under noninductive short-day (SD) photoperiods. The barley <i>elf3</i> mutant displays increased expression of <i>FLOWERING LOCUS T1 (FT1)</i>; however, it remains unclear whether this is the only factor responsible for the early flowering phenotype. We show that the early flowering and vegetative growth phenotypes of the barley <i>elf3</i> mutant are strongly dependent on gibberellin (GA) biosynthesis. Expression of the central GA biosynthesis gene, <i>GA20oxidase2</i>, and production of the bioactive GA, GA₁, were significantly increased in <i>elf3</i> leaves under SDs, relative to the wild type. Inhibition of GA biosynthesis suppressed the early flowering of <i>elf3</i> under SDs independently of <i>FT1</i> and was associated with altered expression of floral identity genes at the developing apex. GA is also required for normal flowering of spring barley under inductive photoperiods, with chemical and genetic attenuation of the GA biosynthesis and signaling pathways suppressing inflorescence development under long-day conditions. These findings illustrate that GA is an important floral promoting signal in barley and that <i>ELF3</i> suppresses flowering under noninductive photoperiods by blocking GA production and <i>FT1</i> expression.