ALTERED RESPONSE TO GRAVITY Is a Peripheral Membrane Protein That Modulates Gravity-Induced Cytoplasmic Alkalinization and Lateral Auxin Transport in Plant Statocytes

Abstract

ARG1 ( ALTERED RESPONSE TO GRAVITY ) is required for normal root and hypocotyl gravitropism. Here, we show that targeting ARG1 to the gravity-perceiving cells of roots or hypocotyls is sufficient to rescue the gravitropic defects in the corresponding organs of arg1-2 null mutants. The cytosolic alkalinization of root cap columella cells that normally occurs very rapidly upon gravistimulation is lacking in arg1-2 mutants. Additionally, vertically grown arg1-2 roots appear to accumulate a greater amount of auxin in an expanded domain of the root cap compared with the wild type, and no detectable lateral auxin gradient develops across mutant root caps in response to gravistimulation. We also demonstrate that ARG1 is a peripheral membrane protein that may share some subcellular compartments in the vesicular trafficking pathway with PIN auxin efflux carriers. These data support our hypothesis that ARG1 is involved early in gravitropic signal transduction within the gravity-perceiving cells, where it influences pH changes and auxin distribution. We propose that ARG1 affects the localization and/or activity of PIN or other proteins involved in lateral auxin transport.

Root Bending Is Antagonistically Affected by Hypoxia and ERF-Mediated Transcription via Auxin Signaling

“…Reduced PIN2 protein abundance may limit basipetal auxin transport and thereby contribute to the increased auxin activity that we observed at the root tip with the DR5:GUS and DII-VENUS reporters in response to hypoxia. Elevated auxin activity at the root tip has been observed in the pin2 mutant (Boonsirichai et al, 2003). Unlike other pin mutants that do not have an altered root gravitropic response, the pin2 mutant shows weakly agravitropic root growth ) that was also observed in this study.…”

OWL1: An Arabidopsis J-Domain Protein Involved in Perception of Very Low Light Fluences

“…(ARL2), are required for root and hypocotyl gravitropism, influencing the distribution of auxin upon stimulation (Sedbrook et al, 1999;Boonsirichai et al, 2003;Guan et al, 2003). At least ARL2 localizes to the plasma membrane.…”

Arabidopsis phosphatidylinositol monophosphate 5-kinase 2 is involved in root gravitropism through regulation of polar auxin transport by affecting the cycling of PIN proteins

“…In agreement with the classic Cholodny-Went theory, recent studies have shown the formation of lateral auxin gradients in Arabidopsis roots upon gravistimulation [64][65][66]. To determine whether the reduced gravity response in pip5k2 is accompanied by an alteration in the asymmetric distribution of auxin in the root tip, GUS activity under gravistimulation was analyzed in WT and pip5k2 seedlings containing the DR5-GUS cassette.…”