Auxin-Induced Plasma Membrane Depolarization Is Regulated by Auxin Transport and Not by AUXIN BINDING PROTEIN1

Abstract

Auxin is a molecule, which controls many aspects of plant development through both transcriptional and non-transcriptional signaling responses. AUXIN BINDING PROTEIN1 (ABP1) is a putative receptor for rapid non-transcriptional auxin-induced changes in plasma membrane depolarization and endocytosis rates. However, the mechanism of ABP1-mediated signaling is poorly understood. Here we show that membrane depolarization and endocytosis inhibition are ABP1-independent responses and that auxin-induced plasma membrane depolarization is instead dependent on the auxin influx carrier AUX1. AUX1 was itself not involved in the regulation of endocytosis. Auxin-dependent depolarization of the plasma membrane was also modulated by the auxin efflux carrier PIN2. These data establish a new connection between auxin transport and non-transcriptional auxin signaling.

The AFB1 auxin receptor controls rapid auxin signaling and root growth through membrane depolarization inArabidopsis thaliana

“…Together these results showed that AUX1-mediated IAA influx and PIN2-mediated efflux contributed to the maintenance of membrane depolarization, possibly by a constitutive cycling of IAA in and out of cells and the associated proton fluxes. In our experiments, the PIN2 mediated efflux was not required for rapid membrane depolarization, a result contradicting previous studies conducted with 10µM IAA in root hairs showing that both aux1 and pin2 mutants are impaired in the membrane potential response (Dindas et al, 2018;Paponov et al, 2019). To put these observations in perspective, these measures were obtained from trichoblasts which might react differently than primary root epidermis.…”

“…The application of the plant growth regulator auxin (IAA) causes almost instantaneous membrane depolarization in various cell types (Goring et al, 1979;Bates and Goldsmith 1983;Felle et al, 1991;Tretyn et al, 1991;Dindas et al, 2018Dindas et al, , 2020Paponov et al, 2019). This qualifies depolarization as a hallmark of the rapid non-transcriptional responses to IAA.…”

Natural Auxin Does Not Inhibit Brefeldin A Induced PIN1 and PIN2 Internalization in Root Cells

“…Most of the mechanistic models that describe auxin-dependent inhibition of endocytosis include ABP1 as a central factor (Pan et al., 2015). These models now require revision in light of the recent demonstration that ABP1 is neither involved in long-term (Gao et al., 2015) nor short-term auxin responses (Paponov et al., 2019). In this work, we provide evidence that the inhibition of endocytosis itself is independent of natural auxin at physiologically relevant concentrations.…”

“…This model provided a mechanistic explanation for the feedback regulation of auxin transport by an auxin-mediated regulation of PIN abundance at the plasma membrane. Although subsequent characterization of the regulation of endocytosis by auxin gave indications for the involvement of auxin-binding protein 1 (ABP1) (Robert et al., 2010), recent evidence has indicated that ABP1 is neither involved in long-term (Gao et al., 2015) nor short-term auxin responses (Paponov et al., 2019). The molecular mechanisms of inhibition of endocytosis by auxin therefore remain poorly understood.…”

Butylated Hydroxytoluene (BHT) Inhibits PIN1 Exocytosis From BFA Compartments in Arabidopsis Roots

“…One of the first candidates for the regulation of PIN endocytosis was auxin itself, based on a positive feedback loop between auxin concentration and auxin transport (Paciorek et al, 2005) and a receptor role for ABP1 in this process (Robert et al, 2010). However, analysis of new abp1 mutants (Gao et al, 2015) showed that the auxin response was independent of ABP1 (Paponov et al, 2019a). Most importantly, the natural auxin IAA only had a very weak influence over this process when compared to the artificial analog 1-NAA, the form of auxin most often used in experiments on the inhibition of endocytosis by auxin (Paponov et al, 2019b).…”