ABSTRACT
Adventitious rooting is a quantitative genetic trait regulated by both environmental and endogenous factors. To better understand the physiological and molecular basis of adventitious rooting, we took advantage of two classes of Arabidopsis thaliana mutants altered in adventitious root formation: the superroot mutants, which spontaneously make adventitious roots, and the argonaute1 (ago1) mutants, which unlike superroot are barely able to form adventitious roots. The defect in adventitious rooting observed in ago1 correlated with light hypersensitivity and the deregulation of auxin homeostasis specifically in the apical part of the seedlings. In particular, a clear reduction in endogenous levels of free indoleacetic acid (IAA) and IAA conjugates was shown. This was correlated with a downregulation of the expression of several auxin-inducible GH3 genes in the hypocotyl of the ago1-3 mutant. We also found that the Auxin Response Factor17 (ARF17) gene, a potential repressor of auxin-inducible genes, was overexpressed in ago1-3 hypocotyls. The characterization of an ARF17-overexpressing line showed that it produced fewer adventitious roots than the wild type and retained a lower expression of GH3 genes. Thus, we suggest that ARF17 negatively regulates adventitious root formation in ago1 mutants by repressing GH3 genes and therefore perturbing auxin homeostasis in a light-dependent manner. These results suggest that ARF17 could be a major regulator of adventitious rooting in Arabidopsis.
Subject(s)
Arabidopsis Proteins/metabolism , Arabidopsis/metabolism , Arabidopsis/radiation effects , Indoleacetic Acids/metabolism , Light , Plant Roots/metabolism , Plant Roots/radiation effects , Arabidopsis/growth & development , Arabidopsis Proteins/genetics , Argonaute Proteins , Down-Regulation/genetics , Down-Regulation/radiation effects , Gene Expression Regulation, Plant/genetics , Gene Expression Regulation, Plant/radiation effects , Homeostasis/genetics , Homeostasis/radiation effects , Mutation/physiology , Mutation/radiation effects , Photic Stimulation , Plant Roots/growth & development , RNA, Messenger/metabolism , Seedlings/growth & development , Seedlings/metabolism , Seedlings/radiation effects , Trans-Activators/metabolismABSTRACT
The FK506-binding proteins (FKBPs) are peptidyl prolyl cis/trans isomerases and the information gathered in the last 10 years reveals their involvement in diverse biological systems affecting the function and structure of target proteins. Members of the FKBP family were shown to be growth-regulated and participate in signal transduction. In this review we have chosen to focus on a few examples of the mammalian and plant systems in which members of the FKBP family have been demonstrated to affect the function of proteins or development. The technologies that enable production of knockout mice, Arabidopsis mutants and overexpression in transgenic organisms have revealed the contribution of FKBP to development in higher eukaryotes. It appears that members of the FKBP family have conserved some of their basic functions in the animal and plant kingdom, whereas other functions became unique. Studies that will take advantage of the full genome sequence available for Arabidopsis and the human genome, DNA chip technologies and the use of transgenic complementation system will contribute to the elucidation of the molecular mechanism and biological function of FKBPs.
