Embryo-lethal phenotypes in early abp1 mutants are due to disruption of the neighboring BSM gene.

Jaroslav Michalko,Marta Dravecká,Jiří Friml,Tobias Bollenbach

doi:10.12688/f1000research.7143.1

Abstract

The Auxin Binding Protein1 (ABP1) has been identified based on its ability to bind auxin with high affinity and studied for a long time as a prime candidate for the extracellular auxin receptor responsible for mediating in particular the fast non-transcriptional auxin responses. However, the contradiction between the embryo-lethal phenotypes of the originally described Arabidopsis T-DNA insertional knock-out alleles ( abp1-1 and abp1-1s) and the wild type-like phenotypes of other recently described loss-of-function alleles ( abp1-c1 and abp1-TD1) questions the biological importance of ABP1 and relevance of the previous genetic studies. Here we show that there is no hidden copy of the ABP1 gene in the Arabidopsis genome but the embryo-lethal phenotypes of abp1-1 and abp1-1s alleles are very similar to the knock-out phenotypes of the neighboring gene, BELAYA SMERT ( BSM). Furthermore, the allelic complementation test between bsm and abp1 alleles shows that the embryo-lethality in the abp1-1 and abp1-1s alleles is caused by the off-target disruption of the BSM locus by the T-DNA insertions. This clarifies the controversy of different phenotypes among published abp1 knock-out alleles and asks for reflections on the developmental role of ABP1.

Highlights

The plant hormone auxin plays a central role in plant growth and development
No hidden copy of the Auxin Binding Protein 1 (ABP1) gene can be found in the genome of A. thaliana One of the possibilities explaining at least some of the recent ABP1 controversies, in particular the strong phenotypes of the conditional lines versus no apparent phenotypes of the abp1-c1 and abp1-TD1 alleles, is the presence of a second, non-annotated ABP1 gene copy in the genome of A. thaliana that is functionally redundant and not disrupted in the abp1-c1 and abp1-TD1 alleles
A non-annotated second copy of the ABP1 gene is present in the sequenced genome of the moss Physcomitrella patens raising the possibility that a similar situation could take a place in the A. thaliana genome

Summary

Introduction

The plant hormone auxin plays a central role in plant growth and development. Sensing and interpreting the fluctuating cellular auxin levels is crucial for mediating the corresponding physiological and developmental responses (Enders & Strader, 2015; Grunewald & Friml, 2010). Two main auxin receptor/co-receptor systems are known and have been proposed to activate a range of cellular responses; among them the Auxin Binding Protein 1 (ABP1) has been considered as a prime candidate for the extracellular auxin receptor (Grones & Friml, 2015). The first notion of ABP1 was based on the auxin-binding activity at the plant cell surface and in the endoplasmic reticulum in crude membrane preparations of etiolated coleoptiles (Hertel et al, 1972). This binding activity was characterized over the decade by detailed biochemical studies (Batt et al, 1976; Ray et al, 1977). ABP1 was firstly purified from maize coleoptile cells (Lobler & Klambt, 1985) as a soluble 22-kDa large glycoprotein and later its crystal structure was elucidated (Woo et al, 2002)

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