ABA Suppresses Root Hair Growth via the OBP4 Transcriptional Regulator

Abstract

Plants modify organ growth and tune morphogenesis in response to various endogenous and environmental cues. At the cellular level, organ growth is often adjusted by alterations in cell growth, but the molecular mechanisms underlying this control remain poorly understood. In this study, we identify the DNA BINDING WITH ONE FINGER (DOF)-type transcription regulator OBF BINDING PROTEIN4 (OBP4) as a repressor of cell growth. Ectopic expression of <i>OBP4</i> in Arabidopsis (<i>Arabidopsis thaliana</i>) inhibits cell growth, resulting in severe dwarfism and the repression of genes involved in the regulation of water transport, root hair development, and stress responses. Among the basic helix-loop-helix transcription factors known to control root hair growth, OBP4 binds the <i>ROOT HAIR DEFECTIVE6-LIKE2</i> (<i>RSL2</i>) promoter to repress its expression. The accumulation of OBP4 proteins is detected in expanding root epidermal cells, and its expression level is increased by the application of abscisic acid (ABA) at concentrations sufficient to inhibit root hair growth. ABA-dependent induction of <i>OBP4</i> is associated with the reduced expression of <i>RSL2</i> Furthermore, ectopic expression of <i>OBP4</i> or loss of <i>RSL2</i> function results in ABA-insensitive root hair growth. Taken together, our results suggest that OBP4-mediated transcriptional repression of <i>RSL2</i> contributes to the ABA-dependent inhibition of root hair growth in Arabidopsis.