Halotropism requires phospholipase Dζ1‐mediated modulation of cellular polarity of auxin transport carriers

Ruud A. Korver,Carlos S. Galvan‐Ampudia,Thea van den Berg,Kirsten H.W.J. ten Tusscher,Christa Testerink,A. Jessica Meyer

doi:10.1111/pce.13646

Ruud A. Korver, Carlos S. Galvan‐Ampudia + Show 4 more

Open Access

https://doi.org/10.1111/pce.13646

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Abstract

Endocytosis and relocalization of auxin carriers represent important mechanisms for adaptive plant growth and developmental responses. Both root gravitropism and halotropism have been shown to be dependent on relocalization of auxin transporters. Following their homology to mammalian phospholipase Ds (PLDs), plant PLDζ‐type enzymes are likely candidates to regulate auxin carrier endocytosis. We investigated root tropic responses for an Arabidopsis pldζ1‐KO mutant and its effect on the dynamics of two auxin transporters during salt stress, that is, PIN2 and AUX1. We found altered root growth and halotropic and gravitropic responses in the absence of PLDζ1 and report a role for PLDζ1 in the polar localization of PIN2. Additionally, irrespective of the genetic background, salt stress induced changes in AUX1 polarity. Utilizing our previous computational model, we found that these novel salt‐induced AUX1 changes contribute to halotropic auxin asymmetry. We also report the formation of “osmotic stress‐induced membrane structures.” These large membrane structures are formed at the plasma membrane shortly after NaCl or sorbitol treatment and have a prolonged presence in a pldζ1 mutant. Taken together, these results show a crucial role for PLDζ1 in both ionic and osmotic stress‐induced auxin carrier dynamics during salt stress.

Highlights

Soil conditions are one of the major decisive factors whether particular crops can be cultivated
We previously reported a salt‐induced increase in internalization and subsequent relocation of the auxin transporter PIN2 on the salt‐exposed side of the root, asymmetrically impacting auxin flow (Galvan‐Ampudia et al, 2013)
Because our experimental results showed that next to salt‐induced changes in PIN2 polarity the baseline PIN2 pattern differed between wild‐type and the pldζ1 mutant roots, we investigated whether the observed differences in basal PIN2 patterning and those induced by salt could explain the observed response differences during halotropism

Summary

| INTRODUCTION

Soil conditions are one of the major decisive factors whether particular crops can be cultivated. Besides adaptation of overall RSA to saline soils, plants are capable of changing their direction of root growth, that is, away from salt, a phenomenon called halotropism (Galvan‐Ampudia et al, 2013). Tissue level auxin patterning critically depends on membrane auxin carriers of the PIN family, exporting auxins out of cells (Blilou et al, 2005), and the AUX/LAX family, importing auxin into cells (Band et al, 2014; Bennett et al, 1996). A possible role for the other ζ‐type PLD, PLDζ1, in plant salt stress responses or tropisms has remained elusive. We identify PLDζ1 as an essential component of root tropisms and reveal their cellular role in auxin carrier and membrane relocalization in response to salinity

| METHODS

| RESULTS

Findings

| DISCUSSION