MEDIATOR16 Orchestrates the STOP1-ALMT1 Signaling Pathway for Plant Adaptation to Phosphate Scarcity in Arabidopsis

Abstract

Phosphate (Pi) is a critical macronutrient for the biochemical and molecular functions of cells. Under Pi limitation, plants manifest adaptive strategies to increase Pi scavenging. However, the molecular mechanisms underlying these responses remain unclear and only a few components have been identified to date. Here, we show that under Pi-scarcity, the MEDIATOR (MED) transcriptional co-activator, through its MED16 subunit, plays a critical role in Arabidopsis root system architecture remodeling, including primary root growth, lateral root formation, and root hair development. Transcriptomic and genetic analyses further revealed that MED16, via a direct interaction with SENSITIVE TO PROTON RHIZOTOXICITY 1 (STOP1), is required for the transcriptional activation of ALUMINUM ACTIVATED MALATE TRANSPORT 1 (ALMT1), a membrane permease, to increase malate exudation in response to low Pi. Our results unravel a critical transcriptional component for understanding how plant cells orchestrate gene expression with the STOP1-ALMT1 module for survival under deficiency of a critical macronutrient.