Strong morphological defects in conditional Arabidopsis abp1 knock-down mutants generated in absence of functional ABP1 protein.

Jaroslav Michalko,Matouš Glanc,Catherine Perrot-Rechenmann,Jiří Friml

doi:10.12688/f1000research.7654.1

Abstract

The Auxin Binding Protein 1 (ABP1) is one of the most studied proteins in plants. Since decades ago, it has been the prime receptor candidate for the plant hormone auxin with a plethora of described functions in auxin signaling and development. The developmental importance of ABP1 has recently been questioned by identification of Arabidopsis thaliana abp1 knock-out alleles that show no obvious phenotypes under normal growth conditions. In this study, we examined the contradiction between the normal growth and development of the abp1 knock-outs and the strong morphological defects observed in three different ethanol-inducible abp1 knock-down mutants ( abp1-AS, SS12K, SS12S). By analyzing segregating populations of abp1 knock-out vs. abp1 knock-down crosses we show that the strong morphological defects that were believed to be the result of conditional down-regulation ofABP1can be reproduced also in the absence of the functional ABP1 protein. This data suggests that the phenotypes in abp1knock-down lines are due to the off-target effects and asks for further reflections on the biological function of ABP1 or alternative explanations for the missing phenotypic defects in the abp1 loss-of-function alleles.

Highlights

The naturally occurring auxin, indole-3-acetic acid, plays a central role in plant growth and development alone or in orchestration with other plant hormones
The biological importance of the Auxin Binding Protein 1 (ABP1) protein as a plasma membrane auxin receptor has been a matter of debates, in part because of its predominant subcellular localization in the endoplasmic reticulum (ER) in maize where the conditions for auxin binding are unfavorable (Habets & Offringa, 2015; Napier et al, 2002)
We show that the morphological phenotypes in SS12S6, SS12K9 and abp1 antisense-based (abp1-AS) can be generated in the absence of functional ABP1 protein and we discuss possible underlying causes of this

Summary

Introduction

The naturally occurring auxin, indole-3-acetic acid, plays a central role in plant growth and development alone or in orchestration with other plant hormones. The biological importance of the ABP1 protein as a plasma membrane auxin receptor has been a matter of debates, in part because of its predominant subcellular localization in the endoplasmic reticulum (ER) in maize where the conditions for auxin binding are unfavorable (Habets & Offringa, 2015; Napier et al, 2002) These discussions were revived by the isolation of two new Arabidopsis abp knock-out alleles, abp1c1 and abp1-TD1 (Gao et al, 2015) that show no obvious phenotypes under standard growth conditions. This correction and the demonstration of normal embryo development in the abp knock-outs (Michalko et al, 2015) suggest that ABP1 plays no essential role in early Arabidopsis embryogenesis

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Conclusion