Involvement of AtGGS1 in GA and glucose signaling by modulating GNL expression.

The MYB-like gene AtGGS1 ( A rabidopsis t haliana G A and g lucose s ignaling) is a DELLA target gene, and also a component of the HXK1 transcriptional complex, implying its roles in gibberellic acid (GA) and glucose signaling. We evaluated the function of AtGGS1 through genetic and biochemical approaches. We conducted phenotypic analyses of the null mutant of AtGGS1 ( atggs1), an AtGGS1 overexpression lines (O/E), and RNA interference (RNAi) lines. The results showed that AtGGS1 inhibited seed germination, root elongation, and leaf expansion. The O/E line flowered earlier and accumulated less chlorophyll than did wild type. The transcript levels of genes encoding GA signaling components, photosynthetic proteins, and glucose sensors and transporters differed among atggs1, O/E, and RNAi lines, as determined by quantitative polymerase chain reaction analyses. AtGGS1 repressed the expression of GNL, which encodes an important player integrating the signaling networks of nutrients (nitrate and glucose) and phytohormones (GA, cytokinin). Genetic and chromatin immunoprecipitation experiments showed that GNL is the direct target of AtGGS1. Our results show that although both AtGGS1 and GNL are downstream of the DELLA/PIF transcription complex and are repressors of GA signaling, AtGGS1 directly regulates the expression of GNL in GA and glucose signaling. [ABSTRACT FROM AUTHOR]