GASA4, a GA-stimulated gene, participates in light signaling in Arabidopsis

Gibberellic acid-stimulated transcripts in Arabidopsis (GASAs) were previously isolated as GA-stimulated transcript 1 from tomato (GAST1) homologs and induced by GA. Here, we report that GASA4 is differentially regulated by light and affected by photoreceptors and light signaling transducers in Arabidopsis. Interestingly, GASA4 was down-regulated by a far-red (FR) light signaling regulator far-red insensitive 219 (FIN219) under all light conditions. GASA4 T-DNA inserted mutant seedlings with undetectable GASA4 transcripts exhibited reduced sensitivity to red (R) and FR light, and can be rescued by the ectopic expression of GASA4; the gasa4 mutant also showed enhanced response to exogenous GA under the same conditions. Furthermore, the gasa4 mutant showed up-regulated expression of several key GA metabolism genes such as GA 20-oxidase 1 (GA20ox1), GA 3-oxidase 1 (GA3ox1) and GA 2-oxidase 2 (GA2ox2), and displayed increased expression of vital flowering time genes, including GI, CO, FT, and SOC1, which leads to an early flowering phenotype under long-day conditions as compared to the wild type. Thus, GASA4, negatively regulated by FIN219, may play various roles to regulate hypocotyl elongation and flowering during Arabidopsis development.