The Ubiquitin E3 Ligase PRU1 Regulates WRKY6 Degradation to Modulate Phosphate Homeostasis in Response to Low-Pi Stress in Arabidopsis

Abstract

Since phosphorus is an essential nutrient for plants, plants have evolved a number of adaptive mechanisms to respond to changes in phosphate (Pi) supply. Previously, we reported that the transcription factor WRKY6 modulates Pi homeostasis by downregulating <i>PHOSPHATE1</i> (<i>PHO1</i>) expression and that WRKY6 is degraded during Pi starvation in <i>Arabidopsis thaliana</i> However, the molecular mechanism underlying low-Pi-induced WRKY6 degradation was unknown. Here, we report that a ubiquitin E3 ligase, PHOSPHATE RESPONSE UBIQUITIN E3 LIGASE1 (PRU1), modulates WRKY6 protein levels in response to low-Pi stress. A <i>pru1</i> mutant was more sensitive than the wild type to Pi-deficient conditions, exhibiting a reduced Pi contents in the shoot, similar to the <i>pho1-2</i> mutant and <i>WRKY6</i>-overexpressing line. PRU1 interacted with WRKY6 in vitro and in vivo. Under low-Pi stress, the ubiquitination and subsequent degradation of WRKY6, as well as the consequential enhancement of <i>PHO1</i> expression, were impaired in <i>pru1</i> PRU1 complementation lines displayed no obvious differences compared with wild-type plants. Further genetic analysis showed that disruption of <i>WRKY6</i> abolished the low-Pi sensitivity of <i>pru1</i>, indicating that WRKY6 functioned downstream of PRU1. Taken together, this study uncovers a mechanism by which PRU1 modulates Pi homeostasis, through regulating the abundance of WRKY6 in response to low-Pi stress in Arabidopsis.