The GATA-type transcription factors GNC and GNL/CGA1 repress gibberellin signaling downstream from DELLA proteins and PHYTOCHROME-INTERACTING FACTORS

<jats:p>The phytohormone gibberellin (GA) regulates various developmental processes in plants such as germination, greening, elongation growth, and flowering time. DELLA proteins, which are degraded in response to GA, repress GA signaling by inhibitory interactions with PHYTOCHROME-INTERACTING FACTOR (PIF) family transcription factors. How GA signaling is controlled downstream from the DELLA and PIF regulators is, at present, unclear. Here, we characterize <jats:italic>GNC</jats:italic> (<jats:italic>GATA, NITRATE-INDUCIBLE, CARBON-METABOLISM INVOLVED</jats:italic>) and <jats:italic>GNL/CGA1</jats:italic> (<jats:italic>GNC-LIKE/CYTOKININ-RESPONSIVE GATA FACTOR1</jats:italic>), two homologous GATA-type transcription factors from <jats:italic>Arabidopsis thaliana</jats:italic> that we initially identified as GA-regulated genes. Our genetic analyses of loss-of-function mutants and overexpression lines establish that <jats:italic>GNC</jats:italic> and <jats:italic>GNL</jats:italic> are functionally redundant regulators of germination, greening, elongation growth and flowering time. We further show by chromatin immunoprecipitation that both genes are potentially direct transcription targets of PIF transcription factors, and that their expression is up-regulated in <jats:italic>pif</jats:italic> mutant backgrounds. In line with a key role of GNC or GNL downstream from DELLA and PIF signaling, we find that their overexpression leads to gene expression changes that largely resemble those observed in a <jats:italic>ga1</jats:italic> biosynthesis mutant or a <jats:italic>pif</jats:italic> quadruple mutant. These findings, together with the fact that <jats:italic>gnc</jats:italic> and <jats:italic>gnl</jats:italic> loss-of-function mutations suppress <jats:italic>ga1</jats:italic> phenotypes, support the hypothesis that GNC and GNL are important repressors of GA signaling downstream from the DELLA and PIF regulators.</jats:p>