Auxin and Light Control of Adventitious Rooting in Arabidopsis Require ARGONAUTE1

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 auxininducible 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.

Auxin Control in the Formation of Adventitious Roots

“…An Arabidopsis transgenic line overexpressing ARF17 developed fewer adventitious roots than wild-type plants, confirming the potential role of ARF genes in the regulation of adventitious root development by auxin (Sorin et al, 2005). It was shown that ARF17, a target of miR160, is a negative regulator, and ARF6 and ARF8, targets of miR167, are positive regulators of adventitious rooting.…”

MicroRNAs and their regulatory roles in animals and plants

“…miR164 regulates auxin signals for lateral root development by targeting NAC mRNA cleavage (Guo et al, 2005). miR167 regulates plant development by negatively regulating the expression of several AUXIN RESPONSE FACTORS (ARF), including ARF 2, ARF 3, ARF 4, ARF 10, ARF 16, and ARF 17 (Mallory et al, 2005;Sorin et al, 2005;Williams et al, 2005a;Yang et al, 2006). miRNAs regulate phase change in plants.…”

Branching Out in Roots: Uncovering Form, Function, and Regulation

“…This adaptive mechanism involves suppressing lateral root initiation on the dry side of a root Bellini et al (2014) and formatting based on Hochholdinger et al (2004b). The original description of the mutant phenotypes detailed in the table can be found in: Boerjan et al (1995), Delarue et al (1998), Fukaki et al (2002), Sorin et al (2005), Sibout et al (2006), Dello Ioio et al (2007), and Negi et al (2010 …”