Gibberellins (GAs) are phytohormones that regulate many aspects of plant growth and development, including germination, elongation, flowering, and floral development. Negative feedback regulation contributes to homeostasis of the GA level. DELLAs are negative regulators of GA signaling and are rapidly degraded in the presence of GAs. DELLAs regulate many target genes, including in Arabidopsis (), encoding the GA-biosynthetic enzyme GA 20-oxidase. As DELLAs do not have an apparent DNA-binding motif, transcription factors that act in association with DELLA are necessary for regulating the target genes. Previous studies have identified GAI-ASSOCIATED FACTOR1 (GAF1) as such a DELLA interactor, with which DELLAs act as coactivators, and was identified as a target gene of the DELLA-GAF1 complex. In this study, electrophoretic mobility shift and chromatin immunoprecipitation assays showed that four GAF1-binding sites exist in the promoter. Using transgenic plants, we further evaluated the contribution of the DELLA-GAF1 complex to GA feedback regulation. Mutations in four GAF1-binding sites abolished the negative feedback of in transgenic plants. Our results showed that GAF1-binding sites are necessary for GA feedback regulation of, suggesting that the DELLA-GAF1 complex is a main component of the GA feedback regulation of .

Animals employ various types of taste receptors to identify and discriminate between different nutritious food chemicals. These macronutrients are thought to fall into 3 major groups: carbohydrates/sugars, proteins/amino acids, and fats. Here, we report that Drosophila larvae exhibit a novel appetitive feeding behavior towards ribose, ribonucleosides, and RNA. We identified members of the gustatory receptor (Gr) subfamily 28 (Gr28), expressed in both external and internal chemosensory neurons as molecular receptors necessary for cellular and appetitive behavioral responses to ribonucleosides and RNA. Specifically, behavioral preference assays show that larvae are strongly attracted to ribose- or RNA-containing agarose in a Gr28-dependent manner. Moreover, Ca2+ imaging experiments reveal that Gr28a-expressing taste neurons are activated by ribose, RNA and some ribonucleosides and that these responses can be conveyed to Gr43aGAL4 fructose-sensing neurons by expressing single members of the Gr28 gene family. Lastly, we establish a critical role in behavioral fitness for the Gr28 genes by showing that Gr28 mutant larvae exhibit low survival rates when challenged to find ribonucleosides in food. Together, our work identifies a novel taste modality dedicated to the detection of RNA and ribonucleosides, nutrients that are essential for survival during the accelerated growth phase of Drosophila larvae.

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