A glycine-rich RNA-binding protein affects gibberellin biosynthesis in Arabidopsis

The RNA-binding protein Arabidopsis thaliana glycine-rich RNA-binding protein 7 (AtGRP7) regulates the steady-state abundance of numerous target transcripts in A. thaliana. Here we show that the GA1 and GA2 transcripts encoding the first enzymes of the gibberellin biosynthetic pathway are expressed at reduced levels in transgenic plants ectopically over-expressing AtGRP7 (AtGRP7-ox plants). Furthermore, the levels of the bioactive phytohormone GA(4) as well as of several intermediates of the GA biosynthetic pathway are reduced in AtGRP7-ox plants. The transgenic plants show a reduced length of the vegetative stem. The application of exogenous GA largely reverses the phenotype by increasing the number of vegetative internodes. AtGRP7-ox plants flower with fewer leaves than wt plants, suggesting that the floral promotive effect of AtGRP7 bypasses the effect of a reduced GA level in AtGRP7-ox plants. Upon GA treatment, AtGRP7-ox plants flower only slightly earlier than wild type plants. Thus, exogenous GA has only a small additional effect in reducing the number of leaves at the onset of flowering in AtGRP7-ox plants.